The present invention relates to a method for preparing 1 ,4-butanediol diesters of the formula (I) defined below by reacting 1 ,4-butanediol with an acylating agent in the absence of any acylation promoters selected from metal- or semi-metal-containing catalysts, triarylcarbenium catalysts, bases and acids which have a stronger acidity than the acid on which the acylation agent is based.

BACKGROUND OF THE INVENTION

1 .4-Butanediol esters, especially 1 ,4-butanediol diacetate, are bulk chemicals and known, for example, from DE 886304 B and DE-A-2525893 as solvents, plasticisers, intermediate compounds, plastics or starting compounds for fragrances and pharmaceutical compositions.

The esters are generally prepared by reacting 1 ,4-butanediol or tetrahydrofuran with a suitable acylating agent (for obtaining 1 ,4-butanediol diacetate for example with acetic acid, glacial acetic acid, acetanhydride or acetyl chloride) in the presence of an acylation promoter, such as a strong acid, also in form of strongly acidic cation exchangers; a base, a (semi)metal catalyst or a triarylcarbenium catalyst.

For instance, in DE 886304 B, 1 ,4-butanediol diacetate is prepared by reacting tetra hydrofuran with glacial acetic acid in the presence of concentrated sulfuric acid and zinc oxide.

S. Xudong et al. describe in Kinetics and Catalysis 2012, 53(3), 301-305 inter alia the reaction of 1 ,4-butanediol with acetic anhydride in the presence of a sulfonic acid groups-containing ionic liquid prepared from TMEDA and 1 ,2-oxathiane-2,2-dioxide.

W. Wang et al. describe in CataL Lett. 2008, 121 , 77-80 inter alia the reaction of 1 ,4- butanediol with acetic anhydride in the presence of a sulfonic acid groups-containing ionic liquid prepared from trimethylamine and 1 ,2-oxathiane-2,2-dioxide.

Z. Yang et al. describe in CataL Lett. 2014, 144, 585-589 inter alia the esterification of

1 .4-butanediol with acetic acid in the presence of a phototungstic acid catalyst.

P. He et al. describe in J. Flow Chem. 2012, 2, 47-51 the acetylation of alcohols, inter alia of 1 ,4-butanediol, with acetic anhydride, using a continuous-flow tungstosilic acid- supported microreactor. S. Zhu describe in J. Catalysis 2013, 306, 155-163 inter alia the esterification of 1 ,4- butanediol with acetic acid in the presence of a silver-exchanged phototungstic acid catalyst.

H. Firouzabadi et al. describe in ChemComm 2003, 764-765 inter alia the esterification of 1 ,4-butanediol with acetic anhydride in the presence of an aluminium dodecatungstphosphate catalyst.

Y. Du et al. describe in Asia-Pac. J. Chem. Eng. 2011 , 6, 933-938 inter alia the esterification of 1 ,4-butanediol with acetic anhydride in the presence of a polythiourethane-based acid.

M.A. Bhosale et al. describe in J. Mol. CataL A Chem 2015, 404-405, 8-17 inter alia the esterification of 1 ,4-butanediol with acetic anhydride in the presence of magnetically separable y-Fe2O3 nanoparticles as catalyst.

H. Firouzabadi et al. describe in J. Mol. CataL A Chem 2008, 289, 61-68 inter alia the esterification of 1 ,4-butanediol with acetic anhydride in the presence of solid trichlorotitanium trifluoromethanesulfonate as catalyst.

T. Srikanth Reddy et al. describe in Tetrahedron Lett. 2006, 47, 6825-6829 inter alia the esterification of 1 ,4-butanediol with acetic anhydride in the presence of La(NO3)3-6H2O as catalyst.

JP 2007-137870 relates to a method for producing carboxylic acid esters from a carboxylic acid and an alcohol using a triarylcarbenium catalyst. Inter alia the esterification of 1 ,4-butanediol with acetic acid in the presence of triphenylcarbenium tetrakis(pentafluorophenyl) borate is described.

FR 3032704 A1 and WO 2016/131846 relate to the preparation of 1 ,3-butadiene from

I ,4-butanediol. The latter is esterified, and the diester is then subjected to pyrolysis. The esterification is carried out by reacting 1 ,4-butanediol with acetic acid in the presence of the acidic catalyst TA801.

WO 2009/ 000723 relates to a process for preparing 1 ,4-butanediol mononitrate by nitration of a C4-C6-alkyl monoester of 1 ,4-butanediol and cleavage of the ester. In comparative examples 6 and 7, 1 ,4-butanediol is reacted with acetic acid or propionic acid in the presence of Amberlyst 15 or Dowex 50 WX2. WO 2003/037321 relates to alkane diol derivatives as therapeutic agents for the treatment of bone conditions. Inter alia, the esterification of 1 ,4-butanediol with acetic anhydride in the presence of pyridine is described.

P. Vinczer et al. describe in Magyar Kemiai Folyoirat 1993, 99(21), 443-457 the acylation of diols in a solvent-free process. In the case of 1 ,4-butanediol as starting diol, the aim of the authors was to enhance the selectivity of the formation of the monoester. 1 ,4-Butanediol is acylated with acetic anhydride or propionic anhydride, which are used in an amount of at most 1 equivalent, mostly of 10 ml/g OH. The reaction is in most cases carried out in the presence of a base, namely KOH, pyridine, triethyl amine or sodium acetate, but reactions in the presence of catalytic amounts of water or of acetic acid are also described.

As the present inventors found, the acid-catalyzed reactions lead to the formation of tetra hydrofuran as side product.

As was recently found, 1 ,4-butanediol diesters of acetic and/or propionic acid have a pleasant aroma and are therefore useful as aroma chemicals. For the use as aroma chemicals, the presence of tetrahydrofuran (THF), even in small amounts, is however not desired for several reasons. For one thing, THF has a strong, ether-like odor even at low concentrations, and adds an off-note to the aroma composition. Moreover, THF is suspected to cause cancer, thus its presence in any application form with which the end user comes into direct contact (as is typically the case for aromatized compositions, such as fragrance compositions, laundry detergents, dishwashing detergents, cosmetics etc.) is to be avoided or at least to be kept as low as possible. Furthermore, THF forms peroxides even in the presence of inhibitors. This can lead to further off-notes and a faster decomposition of the 1 ,4-butanediol diesters.

THF can principally be removed from the 1 ,4-butanediol diester product by distillation. However, this requires an additional tedious and energy-consuming step. Moreover, it was found that in the distillation step, the catalysts mentioned above, especially the acidic ones and especially at higher temperatures, lead to the decomposition of a part of the 1 ,4-butanediol diester to THF and other components, making a distillative separation even more disadvantageous.

Carrying out the reaction in the presence of a base instead of an acidic catalyst is not desirable, either. If an acid is used as acylating agent, the esterifcation reaction does generally not work in the presence of a base. If an acid anyhdride is used, the presence of a base requires the removal of the neutralization products formed from the base and unreacted acid and, if present, excess base. Furthermore, bases may catalyse the hydrolysis of the ester. Moreover, organic bases, such as pyridine or amines, have an unpleasant, persistant odor which is not compatible with the use of 1 ,4-butanediol diesters as aroma chemicals. Analogously, it is not desirable to carry out the reaction in the presence of a (semi)metallic or triarylcarbenium catalyst, since this requires the removal thereof after completion of the reaction. Moreover, (semi)metallic catalysts might also promote THF formation.

It was thus the object of the present invention to provide a simple method for the preparation of 1 ,4-butanediol diesters of acetic and/or propionic acid which avoids or at least suppreses the formation of tetrahydrofuran. It was a further objection of the present invention to use an acylation agent which is economically available from regenerative (renewable) sources.

SUMMARY OF THE INVENTION

This object is surprisingly achieved by carrying out the esterification reaction in the absence of any of the typical acylation promoters, especially in the absence of any acylation promoters selected from metal- or semi-metal-containing catalysts, triarylcarbenium catalysts, bases and acids which have a stronger acidity than the acid R ¹ -C(=O)OH (R ¹ being as defined below). This is surprising, since both esterification and THF formation are catalyzed by acidic catalysts. Accordingly, omitting the acidic catalyst would have been expected to result in a slower conversion rate, but with the same product distribution, and thus also to yield THF.

In one aspect, the present invention relates to a method (termed method A in the following) for preparing a 1 ,4-butanediol diester of the formula (I) where

R ¹ is methyl or ethyl; comprising (a) providing a reaction mixture consisting of

(1.) 1 ,4-butanediol of the formula (II)

(2.) an acylating agent of the formula (III) where

X is -O-C(=O)-R ¹ or -OH;

(3.) optionally a solvent; and

(4.) optionally an entrainer; where the solvent and entrainer are different from water, aqueous solutions, pyridine, triethylamine and ethers; and

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature (to obtain compound (I), of course).

In method A, the reaction mixture provided in step A consists of the components listed above, i.e. the starting compounds (II) and (III), optionally a solvent and optionally entrainer. In the course of the reaction in step (b), no component different from those listed in (a) is added. It is however possible to add in the course of step (b) further or another acylating agent (III), if desired a solvent and/or an entrainer (different from water, aqueous solutions, pyridine, triethylamine and ethers, of course). If the method is carried out (semi)continually, 1 ,4-butanediol (II) is also added in the course of the reaction. If X is OH, water is formed in the course of the reaction in step (b). But except from the water intrinsically present, no further water is added. In a second aspect, the present invention relates to a method (termed method B in the following) for preparing a 1 ,4-butanediol diester of the formula (I) where

R ¹ is methyl or ethyl; comprising reacting 1 ,4-butanediol of the formula (II) with an acylating agent of the formula (III) where

X is -O-C(=O)-R ¹ or -OH; in the absence of any acylation promoters selected from metal- or semi-metal- containing catalysts, triarylcarbenium catalysts, bases and acids which have a stronger acidity than the acid R ¹ -C(=O)OH.

As a matter of course, tetra hydrofuran, which principally can serve as solvent or entrainer in esterification reactions, is not used in any of the reaction steps of the method of the invention, neither as solvent, nor as entrainer nor in any other function.

Both methods A and B relate to esterification reactions which are carried out in the absence of any of the typical acylation promoters, especially of those mentioned in context with method B. In a further aspect, the present invention relates to a method (termed method C in the following) for preparing an aroma chemical composition, comprising preparing a 1 ,4- butanediol diester of the formula (I) as defined above with the method A or B according to the invention, and mixing the 1 ,4-butanediol diester of the formula (I) obtained in said method A or B of the invention with one or more aroma chemicals different from 1 ,4- butanediol diesters of the formula (I) or with a composition comprising one or more of said aroma chemicals or incorporating said 1 ,4-butanediol diester of the formula (I) and said one or more aroma chemicals simultaneously or sequentially into a composition to be aromatized.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The term "Ci-C4-alkyl" indicates a saturated straight-chain or branched aliphatic hydrocarbon radical having 1 to 4 carbon atoms. Examples are methyl, ethyl, propyl, isopropyl, n-butyl, 1 -methylpropyl (sec-butyl), 2-methylpropyl (isobutyl) or 1 ,1 -dimethylethyl (tert-butyl).

Triarylcarbenium catalysts are compounds of the formula Ar ₃ C ⁺ Y", where Ar is an unsubstituted or substituted aromatic ring, such as unsubstituted or substituted phenyl or naphthyl, and Y- is a counter anion, such as a halide, perchlorate, nitrate, sulfate, sulfonate, phosphate, hexafluorophosphate, carboxylate, tetrafluoroborate, tetraaryl borate etc.. Such catalysts are described, for example, in JP 2007-137870.

The solvents and entrainers optionally used in method A are different from water, aqueous solutions, pyridine, triethylamine and ethers. Aqueous solutions are solutions containing water as solvent. Examples are aqueous solutions of bases, acids or buffers. Ethers in this context are ethers customarily used as solvents, such as dimethyl ether, diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, di-tert-butyl ether, methylpropyl ether, methylisopropyl ether, ethylpropyl ether, ethylisopropyl ether, methyl-n-butyl ether, methylisobutyl ether, methyl-tert-butyl ether, ethyl-n-butyl ether, ethylisobutyl ether, ethyl-tert-butyl ether, tetra hydrofuran, 2-methyltetrahydrofuran, 1 ,4- dioxane, morpholine and the like.

Embodiments (E.x) of the invention General and preferred embodiments E.x are summarized in the following, non- exhaustive list. Further preferred embodiments become apparent from the paragraphs following this list.

E.1 . A method for preparing a 1 ,4-butanediol diester of the formula (I) where

R ¹ is methyl or ethyl; comprising

(a) providing a reaction mixture consisting of (1.) 1 ,4-butanediol of the formula (II)

(2.) an acylating agent of the formula (III) where

X is -O-C(=O)-R ¹ or -OH;

(3.) optionally a solvent; and

(4.) optionally an entrainer; where the solvent and entrainer are different from water, aqueous solutions, pyridine, triethylamine and ethers; and

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature.

E.2. A method for preparing a 1 ,4-butanediol diester of the formula (I) where

R ¹ is methyl or ethyl; comprising reacting 1 ,4-butanediol of the formula (II) with an acylating agent of the formula (III) where

X is -O-C(=O)-R ¹ or -OH; in the absence of any acylation promoters selected from metal- or semi-metal- containing catalysts, triarylcarbenium catalysts, bases and acids which have a stronger acidity than the acid R ¹ -C(=O)OH.

E.3. The method according to embodiment E.2, where the acids which have a stronger acidity than the acid R ¹ -C(=O)OH have a pK _a of below 4.75, as determined at 20°C in deionized water at a concentration of 0.001 mol/L. E.4. The method according to any of embodiments E.2 or E.3, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the absence of any substance which has a pK _a of below 6, as determined at 20°C in deionized water at a concentration of 0.001 mol/L.

E.5. The method according to any of the preceding embodiments, where both radicals

R ¹ in compounds (I) have the same meaning.

E.6. The method according to any of the preceding embodiments, where R ¹ is methyl.

E.7. The method according to any of the preceding embodiments, where X is OH.

E.8. The method according to any of the preceding embodiments, where 1 ,4- butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :1 to 1 :10.

E.9. The method according to embodiment E.8, where 1 ,4-butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :1 .5 to 1 :5.

E.10. The method according to embodiment E.9, where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is OH are used in a molar ratio of from 1 :2 to 1 :4.

E.11. The method according to embodiment E.10, where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is OH are used in a molar ratio of from 1 :2.5 to 1 :3.5.

E.12. The method according to embodiment E.11 , where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is OH are used in a molar ratio of approximately 1 :3.

E.13. The method according to embodiment E.9, where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ are used in a molar ratio of from 1 :1 to 1 :4.

E.14. The method according to embodiment E.13, where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ are used in a molar ratio of from 1 :1 to 1 :3.

E.15. The method according to embodiment E.14, where 1 ,4-butanediol and the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ are used in a molar ratio of from 1 :1 to 1 :2.

E.16. The method according to any of the preceding embodiments, where 1 ,4- butanediol is first reacted with an acylating agent of the formula (III) wherein X is OH, and where subsequently, when 50 to 99 mol-% of 1 ,4-butanediol have been converted, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added to the reaction mixture obtained in the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) wherein X is OH. E.17. The method according to embodiment E.16, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added when 70 to 98 mol-% of 1 ,4- butanediol have been converted.

E.18. The method according to embodiment E.17, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added when 90 to 98 mol-% of 1 ,4- butanediol have been converted.

E.19. The method according to any of the preceding embodiments, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out at a temperature of from 80 to 160 °C.

E.20. The method according to embodiment E.19, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out at a temperature of from 100 to 150°C.

E.21 . The method according to embodiment E.20, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out at a temperature of from 110 to 140°C.

E.22. The method according to any of the preceding embodiments, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the presence of an organic solvent and/or of an entrainer, where the solvents and entrainers are different from water, aqueous solutions, pyridine, triethylamine and ethers.

E.23. The method according to embodiment E.22, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the presence of an entrainer if X is OH.

E.24. The method according to embodiment E.22, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the presence of an entrainer (independently of the meaning of X).

E.25. The method according to any of embodiments E.1 to E.23, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the absence of any entrainer if X is -O-C(=O)-R ¹ .

E.26. The method according to any of embodiments E.1 to E.23 and E.25, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the presence of an entrainer if X is OH (the entrainer being a water entrainer, of course) and in the absence of any entrainer if X is -O-C(=O)-R ¹ .

E.27. The method according to any of the preceding embodiments, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the absence of any solvent (the solvent being one without entraining properties for the substance formed in the reaction, i.e. water if X is OH or acid R ¹ -C(O)OH if X is -O-C(=O)-R ¹ , to be more precise). E.28. The method according to any of embodiments E.1 to E.21 , E.25 and E.27, where the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is carried out in the absence of any solvent and entrainer (independently of the meaning of X).

E.29. The method according to any of the preceding embodiments, comprising reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), optionally a solvent and/or optionally an entrainer, where the solvents and entrainers are different from water, aqueous solutions, pyridine, triethylamine and ethers.

E.30. The method according to embodiment E.29, comprising reacting a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III).

E.31 . The method according to embodiment E.29, comprising reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH, an entrainer (the entrainer being a water entrainer, of course) and optionally a solvent.

E.32. The method according to embodiment E.29, comprising reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH or -O-C(=O)-R ¹ , an entrainer (the entrainer being a water or R ¹ -C(O)OH entrainer, of course) and optionally a solvent.

E.33. The method according to embodiment E.29, comprising reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ , and optionally a solvent.

E.34. The method according to any of embodiments E.29 to E.33, where the reaction is carried out in the absence of any solvent (to be more precise in the absence of any solvent with entraining properties for the substance formed in the reaction, i.e. water if X is OH or acid R ¹ -C(O)OH if X is -O-C(=O)-R ¹ ).

E.35. The method according to any of embodiments E.22 to E.34, where the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b , where R ^a is methyl or ethyl and R ^b is Ci-C4-alkyl; benzene, toluene, pentane, hexane, heptane and cyclohexane.

E.36. The method according to embodiment E.35, where X is OH and the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b , where R ^a is methyl or ethyl and R ^b is Ci-C4-alkyl; benzene, toluene, pentane, hexane, heptane and cyclohexane.

E.37. The method according to embodiment E.36, where X is OH and the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b .

E.38. The method according to embodiment E.37, where the entrainer is isopropylacetate. E.39. The method according to any of the preceding embodiments, where the solvent is selected from the group consisting of ketones, sulfoxides, sulfones and mixtures of two or more of the afore-mentioned solvents; preferably from acetone, dimethylsulfoxide, sulfolane and mixtures of two or more of the afore-mentioned solvents.

E.40. The method according to any of the preceding embodiments, comprising

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), optionally a solvent and/or optionally an entrainer;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water or acid formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I).

E.41 . The method according to embodiment E.40, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) and optionally an entrainer is provided.

E.42. The method according to embodiment E.41 , where in step (a) a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), wherein X is OH, and optionally an entrainer is provided.

E.43. The method according to embodiment E.42, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), wherein X is OH, and an entrainer is provided.

E.44. The method according to embodiment E.43, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, acetic acid and optionally an entrainer is provided.

E.45. The method according to embodiment E.44, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, acetic acid and an entrainer is provided.

E.46. The method according to embodiment E.42, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, acetic acid and optionally isopropylacetate is provided.

E.47. The method according to embodiment E.46, where in step (a) a reaction mixture consisting of 1 ,4-butanediol, acetic acid and isopropylacetate is provided.

E.48. The method according to embodiment E.41 , where in step (a) a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III), wherein X is -O-C(=O)-R ¹ , is provided.

E.49. The method according to embodiment E.48, where in step (a) a reaction mixture consisting of 1 ,4-butanediol and acetic anhydride is provided. E.50. The method according to embodiment E.40, comprising

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) where X is OH, and optionally an entrainer; where 1 ,4- butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :2 to 1 :4;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I) if desired.

E.51 . The method according to embodiment E.50, comprising

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) where X is OH, and optionally an entrainer; where 1 ,4- butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :2 to 1 :4;

(b1) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction;

(b2) when 50 to 99 mol-%, preferably 70 to 98 mol-% and in particular 90 to 98 mol-% of the 1 ,4-butanediol provided in step (a) have been converted, adding an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ to the reaction mixture obtained in step (b1);

(b3) reacting the reaction mixture provided in step (b2) at the desired reaction temperature; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I) if desired.

E.52. The method according to any of embodiments E.50 to E.51 , where the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b , where R ^a is methyl or ethyl and R ^b is Ci-C4-alkyl; benzene, toluene, pentane, hexane, heptane and cyclohexane; and is preferably isopropylacetate.

E.53. The method according to any of embodiments E.51 to E.52, where the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ added in step (b2) in an amount of 0.1 to 1 mol per 1 mol of 1 ,4-butanediol provided in step (a). E.54. The method according to embodiment E.53, where the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ added in step (b2) in an amount of 0.3 to 0.7 mol per 1 mol of 1 ,4-butanediol provided in step (a).

E.55. The method according to any of the preceding embodiments, where 1 ,4- butanediol is first reacted with an acylating agent of the formula (III) wherein X is OH, and where subsequently, when 50 to 99 mol-% of 1 ,4-butanediol have been converted, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added to the reaction mixture obtained in the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) wherein X is OH.

E.56. The method according to embodiment E.16, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added when 70 to 98 mol-% of 1 ,4-butanediol have been converted.

E.57. The method according to embodiment E.17, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added when 90 to 98 mol-% of 1 ,4-butanediol have been converted.

E.58. A method for preparing an aroma chemical composition, comprising preparing a 1 ,4-butanediol diester of the formula (I) as defined in any of embodiments E.1 or E.6 with the method according to any of embodiments E.1 to E.57, and mixing the 1 ,4-butanediol diester of the formula (I) obtained in the method according to any of embodiments E.1 to E.57 with one or more aroma chemicals different from butanediol diesters of the formula (I) or with a composition comprising one or more of said aroma chemicals or incorporating said 1 ,4-butanediol diester of the formula (I) and said one or more aroma chemicals simultaneously or sequentially into a composition to be aromatized.

E.59. The method according to embodiment E.58, where the aroma chemicals different from the butanediol diesters of the formula (I) comprise one or more of the following aroma chemicals: geranyl acetate, alpha-hexylcinnamaldehyde, 2-phenoxyethyl isobutyrate, dihydromyrcenol, methyl dihydrojasmonate (preferably with a content of cis isomer of more than 60 wt.%), 4,6,6,7,8,8-hexamethyl- 1 ,3,4,6,7,8-hexahydrocyclopenta[g]benzopyran, tetrahydrolinalool, ethyllinalool, benzyl salicylate, 2-methyl-3-(4-tert-butylphenyl)propanal, cinnamyl alcohol, 4,7-methano-3a,4,5,6,7,7a-hexahydro-5-indenyl acetate, 4,7-methano- 3a,4,5,6,7,7a-hexahydro-6-indenyl acetate, citronellol, citronellyl acetate, tetrahydrogeraniol, vanillin, linalyl acetate, styrolyl acetate, octa hydro-2, 3,8,8- tetramethyl-2-acetonaphthone, 2-acetyl-1 ,2,3,4,6,7,8-octahydro-2,3,8,8- tetramethylnaphthalene, hexyl salicylate, 4-tert-butylcyclohexyl acetate, 2-tert- butylcyclohexyl acetate, alpha-ionone, n-alpha-methylionone, alpha-iso- methylionone, coumarin, terpinyl acetate, 2-phenylethyl alcohol, 4-(4-hydroxy-4- methylpentyl)-3-cyclohexenecarboxaldehyde, alpha-amylcinnamaldehyde, eth- ylene brassylate, (E)-3-methylcyclopentadec-5-enone, (Z)-3-methylcyclopenta- dec-5-enone, 15-pentadec-11 -enolide, 15-pentadec-12-enolide, 15-cyclo- pentadecanolide, 1 -(5,6,7, 8-tetrahydro-3, 5, 5,6,8, 8-hexamethyl-2- naphthalenyl)ethanone, 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol, 2-ethyl-4- (2,2,3-trimethyl-3-cyclopenten-1-yl)-2-buten-1-ol, cis-3-hexenyl acetate, trans-3- hexenyl acetate, trans-2/cis-6-nonadienol, 2,4-dimethyl-3-cyclohexenecarbox- aldehyde, 2,4,4,7-tetramethyloct-6-en-3-one, 2,6-dimethyl-5-hepten-1-al, borneol, 3-(3-isopropylphenyl)butanal, 2-methyl-3-(3,4-methylenedioxyphenyl)propanal, 3-(4-ethylphenyl)-2,2-dimethylpropanal, 7-methyl-2H-1 ,5-benzodioxepin-3(4H)- one, 3,3,5-trimethylcyclohexyl acetate (preferably with a content of cis isomers of 70 wt.% or more), 2,5,5-trimethyl-1 ,2,3,4,4a,5,6,7-octahydronaphthalen-2-ol, 3-(4-/e/7-butylphenyl)-propanal, ethyl 2-methylpentanoate, ethoxymethoxycyclododecane, 2,4-dimethyl-4,4a,5,9b-tetrahydroindeno[1 ,2-d][1 ,3]dioxine, (2-tert- butylcyclohexyl) acetate, 3-[5,5,6-trimethylbicyclo[2.2.1]hept-2-yl]cyclohexan-1-ol, menthone, isomenthone, carvone, camphor, beta-ionone, beta-n-methylionone, beta-isomethylionone, alpha-irone, alpha-damascone, beta-damascone, beta- damascenone, delta-damascone, acetylated cedar wood oil, ambergris tincture, bergamot oil, cedar wood oil, lemon oil, davana oil, ginger oil, lavandin absolute, lavandin oil, lavender absolute, lavender oil, lime oil distilled, lime oil pressed, mandarin oil, clary sage oil, orange blossom absolute, orange oil, patchouli oil, pepper oil, vetiver oil; (E)- and (Z)-3-hexenol, 4-methyl-3-decen- 5-ol, 2-dodecenal, 1 ,1-dimethoxy-2,2,5-trimethyl-4-hexene, 3,7-dimethyl-6- octenenitrile, ethyl acetoacetate, isoamyl acetate, hexyl acetate, isoamyl butyrate, hexyl butyrate, (E)- and (Z)-3-hexenyl isobutyrate, ethyl 2-methylpentanoate, ethyl hexanoate, allyl hexanoate, ethyl (E,Z)-2,4-decadienoate, geraniol, nerol, linalool, geranyl propionate, geranyl butyrate, geranial, neral, nootkatone, 3- methyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)-pentan-2-ol, 3,3-dimethyl-5-(2,2,3- trimethyl-3-cyclopenten-1-yl)-4-penten-2-ol, cedryl methyl ether, 3a, 6, 6,9a- tetramethyldodecahydronaphtho[2,1-b]furan, rose oxide, 6,7-dihydro-1 ,1 ,2,3,3- pentamethyl-4(5H)-indanone, 1 -(5,5-dimethyl-1 -cyclohexen-1 -yl)-4-penten-1 -one, 4,7-methano-3a,4,5,6,7,7a-hexahydro-5- or 6-indenyl propionate, 4,7- methanooctahydro-5- or 6-indenyl acetate, allyl 3-cyclohexylpropionate, 1- phenylethyl alcohol, benzyl acetate, 1 -phenylethyl acetate, alpha, alphadimethylphenylethyl acetate, alpha, alpha-dimethylphenylethyl butyrate, 2,4,6- trimethyl-4-phenyl-1 ,3-dioxane, 2-methyl-3-(4-isopropylphenyl)-propanal, cin- namaldehyde, 4-(4-hydroxyphenyl)-2-butanone, phenylethyl phenylacetate, ethyl 3-methyl-3-phenylglycidate, estragole, anethole, eugenol, 3-hydroxy-2-methyl- 4H-pyran-4-one, 2-ethyl-3-hydroxy-4H-pyran-4-one, 1 ,4-decanolide, 1 ,4- undecanolide, 1 ,15-pentadecanolide, coumarin.

Unless stated otherwise, the below remarks apply both to methods A and B and, as far as applicable, also to method C.

As already explained, in method A, the reaction mixture provided in step (a) consists of the components listed above, i.e. the starting compounds (II) and (III), optionally a solvent and optionally entrainer. In the course of the reaction in step (b), no component different from those listed in (a) is added. It is however possible to add in the course of step (b) further or another acylating agent (III), if desired a solvent and/or an entrainer (different from water, aqueous solutions, pyridine, triethylamine and ethers, of course). If method A is carried out (semi)continually, 1 ,4-butanediol (II) is also added in the course of the reaction.

Providing a reaction mixture consisting of 1 ,4-butanediol (II), the acylation agent (III) optionally a solvent and optionally an entrainer (as worded for step (a) in method A or in preferred embodiments of method B) is thus not restricted to providing all of the listed components at once, at the beginning of the reaction, but encompasses operation modes where some or all of the listed components are provided by and by. For example, mixing 1 ,4-butanediol (II) with the acylation agent (III) might be exothermic, and thus it might be expedient to add the acylation agent (III) by and by, also during or after the reaction mixture has been brought to the desired temperature. “Consisting of’ precludes however any component different from those listed being added before the esterification is terminated.

The solvents and entrainers optionally used in method A (and also in an embodiment of method B) are inter alia different from water and aqueous solutions. This does however not mean that the reaction mixture does not contain water: If X is OH, water is of course formed in the esterification reaction. The condition that the optional solvents and entrainers are different from water and aqueous solutions just excludes their being added to the reaction mixture (minor amounts of water may however be present if the starting compounds, entrainer(s) and/or solvent(s) are not completely anhydrous).

The above exclusion relates to the proper esterification. After completion of the esterification reaction to the desired degree, said exclusion no longer applies. For example, aqueous basic solutions can be used to neutralize the obtained reaction mixture (e.g. if the acylation agent has been used in excess). According to method B of the invention, the esterification of 1 ,4-butanediol is carried out in the absence of any of the typical acylation promoters (often also termed as esterification catalysts, although in the case of bases these are generally used in at least stoichiometric amounts and do thus not fall under the definition of catalysts in the proper sense), to be more precise in the absence of acylation promoters selected from metal- or semi-metal-containing catalysts, triarylcarbenium catalysts, bases and acids which have a stronger acidity than the acid R ¹ -C(=O)OH.

In method A, these acylation promoters are of course also absent in the esterification of 1 ,4-butanediol (II).

These acylation promoters have to be absent during the proper esterification reaction. As soon as esterification has been completed, their absence is no longer mandatory and they can be used, for example, in a subsequent work-up step. For instance, after completion of the esterification reaction, bases can be used in a subsequent work-up step to neutralize excess acid.

Since R ¹ -C(=O)OH is either acetic acid with a pK _a of 4.75 or propionic acid with a pK _a of 4.87, acids which have a stronger acidity than the acid R ¹ -C(=O)OH can principally be defined as acids with a pK _a of below 4.75 [if acetic acid or acetanhydride, optionally in admixture with propionic acid and/or propionic acid anhydride is used as compound (III)] or of below 4.87 [if propionic acid or propionic acid anhydride is used as compound (III)]. pK _a values as indicated herein generally relate to values as determined at 20°C in deionized water at a concentration of 0.001 mol/L. If pK _a values cannot be determined under these conditions, for example because the acid in question is not (sufficiently) soluble or not sufficiently stable in water, pK _a values as known in the art and as obtained, for example, in another solvent system and/or at another temperature, can be taken as a basis instead.

In case of polymeric acids, e.g. of acidic ion exchangers, for which pK _a values are not readily available, those with sulfonic acid groups have generally a stronger acidity than the acid R ¹ -C(=O)OH and are thus not allowed in the present acylation (esterification) step, whereas those with carboxylic acid groups have generally a weaker acidity than the acid R ¹ -C(=O)OH. Nevertheless, preferably, no polymeric acids of any type, in particular no acidic ion exchangers of any type are present in the acylation (esterification) step. Preferably, the acylation reaction is carried out in the absence of any acids (different from R ¹ COOH of course) with a pK _a of below 4.75, as determined at 20°C in deionized water at a concentration of 0.001 mol/L or, if the pK _a is not available under these conditions, as documented in the art. More preferably, the acylation reaction is carried out in the absence of any substance which has a pK _a of below 6 (“any substance” means of course any substance different from the present compounds (I), (II) and in particular (III)).

In compounds (I), the two radicals R ¹ can have the same or different meanings (i.e. one of R ¹ is methyl and the other is ethyl). To obtain compounds (I) in which the two R ¹ have different meanings, a mixture of different compounds (III), where in one compound (III) of said mixture R ¹ is methyl and in another compound (III) R ¹ is ethyl, has to be used.

Preferably however, both radicals R ¹ in compounds (I) have the same meaning.

Preferably, R ¹ is methyl.

If in compounds (III) X is OH, the compound (III) is an acid, to be more precise acetic acid or propionic acid.

If in compounds (III) X is -O-C(=O)-R ¹ , the compound (III) is an acid anhydride, to be more precise acetic acid anhydride (acetanhydride) or propionic acid anhydride.

Preferably, X is OH.

More preferably, in compounds (III), R ¹ is methyl and X is OH, compound (III) thus more preferably being acetic acid.

1 ,4-Butanediol and the acylating agent of the formula (III) are preferably used in a molar ratio of from 1 :1 to 1 :10, more preferably from 1 :1.5 to 1 :5. In case that X is OH, 1 ,4- butanediol and the acylating agent of the formula (III) are even more preferably used in a molar ratio of from 1 :2 to 1 :4, particularly preferably from 1 :2.5 to 1 :3.5, and in particular in a molar ratio of approximately 1 :3. In case that X is -O-C(=O)-R ¹ , 1 ,4-butanediol and the acylating agent of the formula (III) are even more preferably used in a molar ratio of from 1 :1 to 1 :4, particularly preferably from 1 :1 to 1 :3, and in particular from 1 :1 to 1 :2. “Approximately” in this context is intended to include deviations from ideal stoichiometry caused, for example, by weighing errors. Such errors are in general below 10%, mostly below 5% or even below 2%.

Using the acid (III) (X = OH), and especially acetic acid, as acetylating agent has the advantage that this is economically obtainable from purely regenerative (= renewable; bio-based) sources in a simple and cost-effective manner, while the anhydride (X = -O- C(=O)-R ¹ ) needs at least a further, energy-intensive synthetic step and is thus distinctly less economic.

The carboxylic acids R ¹ -C(=O)-OH are found abundantly in nature. Acetic acid can moreover be obtained from the oxidation of ethanol which can in turn be obtained from the fermentation of any sugar- or starch-containing crop, such as fruits and cereals. Propionic acid can be obtained via fermentation processes of various sugars, such as glucose, xylose, maltose, sucrose and whey lactose.

Moreover, also 1 ,4-butanediol can be obtained from renewable sources and is commercially available. Known methods start for example from furfural (furan-2-aldehyde), which is in turn obtained from carbohydrates, for example from pentoses contained in many plant materials (most often agricultural byproducts like sugarcane bagasse and corn cobs are used) which are dehydrated with sulfuric acid. The production of wood pulp with the magnesium bisulfite process also yields high amounts of furfural. Furfural can be converted to furan, which can be hydrogenated and ring-opened to 1 ,4- butanediol. Alternatively, succinic acid or polyhydroxy butyric acid obtained from fermentation processes can be hydrogenated to 1 ,4-butanediol, either directly or via y- butyrolactone and THF. Succinic acid can be obtained from fermentation (using e.g. various bacterial strains) of biomass, e.g. from sugars (e.g. sucrose, raffinose, fructose, glucose, galactose, lactose, mannose, xylose, arabinose) or glycerol (obtained in turn from vegetable/animal oils or fats). Also the direct fermentation of sugars can give 1 ,4- butanediol.

The origin of the acylating agent, 1 ,4-butanediol or its ester from a renewable source can be verified, for example, by radiocarbon dating. Generally, the molar ratio of the ¹² C isotope to the ¹⁴ C isotope is used as an indicator. In living organisms, the molar ratio of the ¹² C isotope to the ¹⁴ C isotope is approximately 1 x ¹² : 1 (to be more precise 1 xio ¹² : 1.25). Thus, the content of the ¹⁴ C isotope in the 1 ,4-butanediol ester or the starting material (II) and/or (III) will be at a detectable level if at least part thereof is derived from a renewable source. Suitable methods for determining the content of the ¹⁴ C isotope are known in the art and deliver generally comparable results. For example, the method according to ASTM D6866-21 can be used; this method was specifically developed for determining the content of bio-based/biogenic carbon in bioproducts. However, other methods are suitable as well. The detection level of the available methods of the content of the ¹⁴ C isotope is such that it allows radiocarbon dating between ca. 300 and 60000 before the present time, which is very remote from the age of fossil carbon sources. Thus, any detected ¹⁴ C isotope is an indicator of a renewable origin of the 1 ,4-butanediol esters.

While using the acid (III) (X = OH), and especially acetic acid, as acylation agent is desirable from an environmental view and from the view of inexpensive starting materials, full conversion of 1 ,4-butanediol is obtained on the other hand at a higher rate when acid anhydride (X = -O-C(=O)-R ¹ ) is used as acylation agent.

It was found that a higher conversion rate can also be obtained if first the acid (III) (X = OH) is used as acetylating agent, and, after a certain amount of the compound (II) has been converted (but before full conversion, of course), the corresponding anhydride, i.e. the compound (III) wherein X = -O-C(=O)-R ¹ (and wherein R ¹ has expediently the same meaning as in the acid (III)) is added.

Thus, in a preferred embodiment of methods (A) and (B), 1 ,4-butanediol is first reacted with an acylating agent of the formula (III) wherein X is OH, and subsequently, when 50 to 99 mol-%, preferably 70 to 98 mol-% and in particular 90 to 98 mol-% of 1 ,4- butanediol (of the total amount of 1 ,4-butanediol used in the reaction, of course) have been converted, an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added to the reaction mixture obtained in the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) wherein X is OH. The reaction is then continued.

In this variant, 1 ,4-butanediol and the first-used acylating agent of the formula (III) wherein X is OH are preferably used in a molar ratio of from 1 :2 to 1 :4, more preferably from 1 :2.5 to 1 :3.5, and in particular in a molar ratio of approximately 1 :3, and the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added to the reaction mixture obtained in the reaction of 1 ,4-butanediol with the acylating agent of the formula (III) wherein X is OH in an amount of 0.1 to 1 mol per 1 mol of 1 ,4-butanediol, more preferably in an amount of 0.3 to 0.7 mol per 1 mol of 1 ,4-butanediol (to be precise per 1 mol of the total amount of 1 ,4-butanediol to be reacted, and not of the amount remaining after acylation with the first-used acylating agent). The reaction of 1 ,4-butanediol with the acylating agent of the formula (III) is preferably carried out at a temperature of from 80 to 160 °C, more preferably from 100 to 150°C, in particular from 110 to 140°C.

The reaction pressure is not critical and can range for example from 0.01 to 30 bar. Expediently, the reaction is carried out at atmospheric pressure. Atmospheric pressure means the local ambient pressure, and thus roughly 1013.25 hPa ± 200 hPa.

The reaction of 1 ,4-butanediol with the acylating agent of the formula (III) can be carried out in the presence of a solvent and/or of an entrainer, where the solvents and entrainers are different from water, aqueous solutions, pyridine, triethylamine and ethers.

Entrainers in terms of the present invention are compounds (generally specific solvents) which form with the water (if X is OH) or the acid R ¹ COOH (if X is -O-C(=O)-R ¹ ) formed in the esterification reaction an azeotrope and which are not or only scarcely miscible with water or the acid R ¹ COOH. The azeotrope can be distilled off and thus furthers the esterification.

Suitable entrainers are for example esters of the formula R ^a -C(=O)-O-R ^b , where R ^a is methyl or ethyl and R ^b is Ci-C4-alkyl; benzene, toluene, pentane, hexane, heptane, cyclohexane, trichloromethane, tetrachloromethane and mixtures thereof. Among these, preference is given to esters R ^a -C(=O)-O-R ^b , benzene, toluene, pentane, hexane, heptane, cyclohexane and mixtures thereof. If X is OH, and the substance to be entrained is water, any of the above-listed entrainers is suitable. If X is -O-C(=O)-R ¹ , and the substance to be entrained is the acid R ¹ COOH, the entrainer is suitably benzene, toluene, hexane, heptane, cyclohexane, tetrachloromethane or a mixture thereof; preferably benzene, toluene, hexane, heptane cyclohexane or a mixture thereof; and in particular toluene if R ¹ is methyl, and is suitably heptane if R ² is ethyl.

Preferably, the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b , especially if X is OH (and thus the substance to be entrained is water). More preferably, the entrainer is isopropylacetate, especially if X is OH (and thus the substance to be entrained is water).

The entrainers can also serve as solvents. Thus, the presence of a further solvent is principally not necessary if an entrainer is used.

If desired, a solvent can nevertheless be used. As explained above, entrainers are generally specific solvents. Solvents in this context are thus solvents with no entraining properties for the substances to be entrained (water or acid R ¹ COOH).

Suitable solvents different from the entrainers are for example ketones, such as acetone; sulfoxides, such as dimethylsulfoxides, sulfones, such as sulfolane, or mixtures of two or more of the afore-mentioned solvents.

Entraining water is more beneficial for the esterification reaction than entraining the acid R ¹ COOH. Therefore, carrying out the esterification reaction in the presence of an entrainer is a preferred option when X is OH (and thus the substance to be entrained is water).

Thus, in a preferred embodiment, the reaction is carried out in the presence of an entrainer if X is OH (the entrainer being a water entrainer, of course).

In a more preferred embodiment, the reaction is carried out in the presence of an entrainer if X is OH (the entrainer being a water entrainer, of course) and in the absence of an entrainer if X is -O-C(=O)-R ¹ .

In a preferred embodiment, the reaction is carried out in the absence of any solvent (solvent meaning solvent without entraining properties for the substance formed in the reaction, i.e. water if X is OH or acid R ¹ -C(O)OH if X is -O-C(=O)-R ¹ ).

In yet another preferred embodiment, the reaction is carried out without any entrainer or solvent; i.e. neat (independently of the meaning of X).

In particular, the reaction is carried out in the presence of an entrainer if X is OH (the entrainer being a water entrainer, of course), in the absence of an entrainer if X is -O-C(=O)-R ¹ , and, independently of the meaning of X, in the absence of any solvent (solvent meaning solvent without entraining properties for the substance formed in the reaction, i.e. water if X is OH or acid R ¹ -C(O)OH if X is -O-C(=O)-R ¹ ).

If 1 ,4-butanediol is first reacted with an acylating agent of the formula (III) wherein X is OH, and subsequently, when 50 to 99 mol-%, preferably 70 to 98 mol-% and in particular 90 to 98 mol-% of 1 ,4-butanediol have been converted, with an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ , the reaction can be carried out in the presence or absence of an entrainer. Independently therefrom, the reaction is preferably carried out in the absence of any solvent (solvent meaning solvent without entraining properties for the substance formed in the reaction, i.e. water if X is OH or acid R ¹ - C(O)OH if X is -O-C(=O)-R ¹ ).

If an entrainer is used, this is preferably used in an amount of at least 5 mol-% of that amount (in mol) which is necessary to form the respective azeotropic mixture with the theoretically formed amount of water (if X = OH) or acid (if X = O-C(O)R ¹ ). Preferably, the entrainer is used in an amount of at least 10 mol-% of that amount which is necessary to form the respective azeotropic mixture with the theoretically formed amount of water (if X = OH) or acid (if X = O-C(O)R ¹ ) to up to a 20-fold excess of the amount necessary to form the respective azeotropic mixture, preferably up to a 10-fold excess, more preferably up to a 5-fold excess. If the entrainer is however also to serve as solvent, the excess can of course be distinctly larger if desired.

If the entrainer is used in an amount of less than the equivalent amount (i.e. in an amount of less than 100 mol-% of that amount which is necessary to form the respective azeotropic mixture with the theoretically formed amount of water (if X = OH) or acid (if X = O-C(O)R ¹ )), the entrainer removed via azeotropic distillation from the reaction is preferably separated from the entrained water or acid and reintroduced into the reaction. For example, the azeotrope distilled off the reaction is introduced continually or periodically into a separator, and the entrainer is separated from the entrained substance (generally water) and recirculated to the reaction. This works particularly well if entrainer and entrained substance are not or scarcely miscible with each other or have a miscibility gap at a temperature to which the separator can be reasonably cooled. An example for a separator on a laboratory scale is a Dean-Stark apparatus. The separation need not be perfect; it is sufficient to separate the entrainer from a substantial amount of the entrained substance; a “substantial amount” being 70 mol-% or more, preferably 80 mol-% or more.

In a preferred embodiment, the method B of the invention comprises reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), optionally a solvent and/or optionally an entrainer, where the solvents and entrainers are different from water, aqueous solutions, pyridine, triethylamine and ethers (in method A this is anyway mandatory). The reaction mixture of this embodiment contains thus no other components than 1 ,4-butanediol, an acylating agent of the formula (III), optionally a solvent and/or optionally an entrainer. In a more preferred embodiment, the method of the invention (methods A and B in this case) comprises reacting a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ (and no other component).

In another more preferred embodiment, the method of the invention (methods A and B in this case) comprises reacting a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III) (and no other component).

In an alternatively more preferred embodiment, the method of the invention (methods A and B in this case) comprises reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH and an entrainer (and no other component).

In an alternatively more preferred embodiment, the method of the invention (methods A and B in this case) comprises reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) and an entrainer (and no other component).

Even more preferably, the method of the invention (methods A and B in this case) comprises reacting a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH and an entrainer (and no other component); or reacting a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ (and no other component).

1 ,4-Butanediol and the acylating agent (III) are generally brought to reaction by bringing them into contact (e.g. by mixing them), if desired in the presence of a solvent and/or an entrainer, and heating the reaction mixture, preferably to the reaction temperature indicated above. Alternatively, the reagents can be added gradually, especially in the case of a continuous or semi-continuous process.

If an entrainer is present, the azeotrope formed by the entrainer and the water or acid formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is generally distilled off continually or periodically to remove the water or acid R ¹ COOH formed in the esterification reaction and thus promote the ester formation. If desired, the entrainer is separated from the azeotrope which has been distilled off and is reintroduced into the reaction.

If necessary, further entrainer is added continually or periodically in the course of the reaction to compensate its depletion. If no entrainer is used, it is possible to remove or not to remove the water or acid formed in the esterification process. Removal is generally carried out by distillation, and can be carried out continually or periodically.

If however 1 ,4-butanediol is first reacted with an acylating agent of the formula (III) wherein X is OH, and subsequently with an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ , then water formed in the reaction of 1 ,4-butanediol with the acid (III) (X = OH) is expediently removed before the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added, e.g. continually or periodically in the course of the reaction of 1 ,4-butanediol with the acid (III) or just in one step before the anhydride (III) is added, since otherwise the anhydride (III) might be at least partially hydrolized by said reaction water.

The suitable reaction time depends on the specific reaction conditions and can be determined by those skilled in the art, e.g. by continuously or periodically checking the progress of reaction with usual means (e.g. TLC, GC etc.), by measuring the amount of distilled azeotrope (if an entrainer is used) and the like. The reaction time ranges generally from 1h to 100 h, preferably from 5 h to 50 h, e.g. from 10 h to 30 h.

After completion of the reaction to the desired degree, the reaction mixture is worked- up and the compound of the formula (I) is isolated if desired. Work-up can be carried out by usual means, such as neutralization, e.g. if an acid anhydride has been used as compound (III) and no entrainer for the acid has been used, or if excess acid has been used; separation from water if an acid has been used as compound (III) and no water entrainer has been used or water has not been removed, e.g. by phase separation, distillation etc.; filtration, extraction, removal of the solvent, entrainer and/or unreacted starting material etc.. The suitable work-up depends on the starting materials used and if one thereof has been used in excess, on the presence or absence of entrainer or solvent etc. and can be determined by the skilled person.

The product can be isolated and purified by known means, such as extractive, distilla- tive or chromatographic methods.

Thus, in a preferred embodiment, the method (A and B) comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III), optionally a solvent and/or optionally an entrainer;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water or acid formed in the reaction of 1 ,4- butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired.

More preferably, in step (a) a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III) is provided.

In an alternative more preferred embodiment, in step (a) a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) and an entrainer is provided, especially if X is OH.

Thus, more preferably, the method comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) and optionally an entrainer;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water or acid formed in the reaction of 1 ,4- butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired.

Even more preferably, the method comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH and optionally an entrainer; where preferably an entrainer is provided; or providing a reaction mixture consisting of 1 ,4-butanediol and an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ ;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired. Particularly preferably, the method comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) wherein X is OH and optionally an entrainer; where preferably an entrainer is provided;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired.

In particular, the method comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, acetic acid and optionally isopropyl acetate as entrainer; where preferably isopropyl acetate is provided;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and acetic acid is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired.

Specifically, the method comprises:

(a) providing a reaction mixture consisting of 1 ,4-butanediol, acetic acid and optionally isopropyl acetate as entrainer, where 1 ,4-butanediol and acetic acid are provided in a molar ratio of from 1 :1 to 1 : 10, more preferably from 1 :1.5 to 1 :5, even more preferably from 1 :2 to 1 :4, particularly preferably from 1 :2.5 to 1 :3.5, and in particular in a molar ratio of approximately 1 :3; and the entrainer, if present, is provided in an amount of from 10 to 1000 mol-%, preferably from 20 to 300 mol.- %, more preferably from 20 to 100 mol-%, even more preferably from 20 to 50 mol-%, in particular from 25 to 40 mol-%, relative to the amount (in mol; this amount corresponds to 100 mol-%) of 1 ,4-butanediol;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and acetic acid is removed via continual or periodical distillation from the reac- tion; where in case that the entrainer has been provided in an amount of at most 275 mol-%, relative to the amount (in mol; this amount corresponds to 100 mol- %) of 1 ,4-butanediol, the entrainer is preferably separated from the removed azeotrope and reintroduced into the reaction mixture; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I), if desired.

In another preferred embodiment, the method comprises

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) where X is OH, and optionally an entrainer; where 1 ,4-butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :2 to 1 :4;

(b) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction; and

(c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I) if desired.

In another preferred embodiment, the method comprises

(a) providing a reaction mixture consisting of 1 ,4-butanediol, an acylating agent of the formula (III) where X is OH, and optionally an entrainer; where 1 ,4-butanediol and the acylating agent of the formula (III) are used in a molar ratio of from 1 :2 to 1 :4;

(b1 ) reacting the reaction mixture provided in step (a) at the desired reaction temperature; where in case that an entrainer has been provided in step (a), the azeotrope formed by the entrainer and the water formed in the reaction of 1 ,4-butanediol and the acylating agent of the formula (III) is removed via continual or periodical distillation from the reaction;

(b2) when 50 to 99 mol-%, preferably 70 to 98 mol-% and in particular 90 to 98 mol-% of the 1 ,4-butanediol provided in step (a) have been converted, adding an acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ to the reaction mixture obtained in step (b1 );

(b3) reacting the reaction mixture provided in step (b2) at the desired reaction temperature; and (c) after completion of the reaction to the desired degree working-up the reaction mixture obtained in step (b) and isolating the compound of the formula (I) if desired.

In case that water has not been removed in step (b1), it is expedient to remove the water before the acylating agent of the formula (III) wherein X is -O-C(=O)-R ¹ is added, since otherwise the latter would be hydrolized.

Preferably, the entrainer is selected from the group consisting of esters of the formula R ^a -C(=O)-O-R ^b , where R ^a is methyl or ethyl and R ^b is Ci-C4-alkyl; benzene, toluene, pentane, hexane, heptane and cyclohexane; and is preferably isopropylacetate.

The invention relates moreover to a method for preparing an aroma chemical composition, comprising preparing a 1 ,4-butanediol diester of the formula (I) as defined above with the method A or B according to the invention, and mixing the 1 ,4-butanediol diester of the formula (I) obtained in the method A or B according to the invention with one or more aroma chemicals different from the 1 ,4-butanediol diesters of the formula (I) or with a composition comprising one or more of said aroma chemicals or incorporating said 1 ,4-butanediol diester of the formula (I) and said one or more aroma chemicals simultaneously or sequentially into a composition to be aromatized.

Suitable aroma chemicals different from the 1 ,4-butanediol diesters of the formula (I) are the following:

Geranyl acetate (3,7-dimethyl-2,6 octadien-1yl acetate), alpha-hexylcinnamaldehyde, 2-phenoxyethyl isobutyrate (Phenirat ¹ ), dihydromyrcenol (2,6-dimethyl-7-octen-2-ol), methyl dihydrojasmonate (preferably with a content of cis isomer of more than 60 wt.%) (Hedione ⁹ , Hedione HC ⁹ ), 4,6,6,7,8,8-hexamethyl-1 ,3,4,6,7,8-hexahydro- cyclopenta[g]benzopyran (Galaxolid ³ ), tetrahydrolinalool (3,7-dimethyloctan-3-ol), ethyllinalool, benzyl salicylate, 2-methyl-3-(4-tert-butylphenyl)propanal (Lysmeral ² ), cinnam- yl alcohol, 4,7-methano-3a,4,5,6,7,7a-hexahydro-5-indenyl acetate and/or 4,7-methano-3a,4,5,6,7,7a-hexahydro-6-indenyl acetate (Herbaflorat ¹ ), citronellol, cit- ronellyl acetate, tetrahydrogeraniol, vanillin, linalyl acetate, styrolyl acetate (1 -phenylethyl acetate), octahydro-2, 3, 8, 8-tetramethyl-2-acetonaphthone and/or 2-acetyl-1 ,2,3,4,6,7,8-octahydro-2,3,8,8-tetramethylnaphthalene (Iso E Super ³ ), hexyl salicylate, 4-tert-butylcyclohexyl acetate (Oryclone ¹ ), 2-tert-butylcyclohexyl acetate (Agrumex HC ¹ ), alpha-ionone (4-(2,2,6-trimethyl-2-cyclohexen-1-yl)-3-buten-2-one), n-alpha-methylionone, alpha-isomethylionone, coumarin, terpinyl acetate, 2-phenylethyl alcohol, 4-(4-hydroxy-4-methylpentyl)-3-cyclohexenecarboxaldehyde (Lyral ³ ), alpha-amylcinnamaldehyde, ethylene brassylate, (E)- and/or (Z)-3-methyl- cyclopentadec-5-enone (Muscenon ⁹ ), 15-pentadec-11 -enolide and/or 15-pentadec-12- enolide (Globalide ¹ ), 15-cyclopentadecanolide (Macrolide ¹ ), 1-(5,6,7,8-tetrahydro- 3,5,5,6,8,8-hexamethyl-2-naphthalenyl)ethanone (T onalid ¹⁰ ), 2-isobutyl-4-methyl- tetrahydro-2H-pyran-4-ol (F lord ⁹ ) , 2-ethyl-4-(2,2,3-trimethyl-3-cyclopenten-1 -yl)-2- buten-1-ol (Sandolen ¹ ), cis-3-hexenyl acetate, trans-3-hexenyl acetate, trans-2/cis-6- nonadienol, 2,4-dimethyl-3-cyclohexenecarboxaldehyde (Vertocitral ¹ ), 2,4,4,7-tetra- methyloct-6-en-3-one (Claritone ¹ ), 2,6-dimethyl-5-hepten-1-al (Melonal ² ), borneol, 3-(3-isopropylphenyl)butanal (Florhydral ² ), 2-methyl-3-(3,4-methylenedioxyphenyl)- propanal (Helional ³ ), 3-(4-ethylphenyl)-2,2-dimethylpropanal (Florazon ¹ ), 7-methyl- 2H-1 ,5-benzodioxepin-3(4H)-one (Calone), 3,3,5-trimethylcyclohexyl acetate (preferably with a content of cis isomers of 70 wt.%) or more, 2,5,5-trimethyl-1 , 2, 3, 4, 4a, 5,6,7- octahydronaphthalen-2-ol (Ambrinol S ¹ ), 3-(4-/e/7-butylphenyl)-propanal (Bourgeonal ⁴ ), ethyl 2-methylpentanoate (Manzanate ⁴ ), ethoxymethoxycyclododecane (Amberwood ¹ ), 2,4-dimethyl-4,4a,5,9b-tetrahydroindeno[1 ,2-d][1 ,3]dioxine (Magnolan ¹ ), (2-tert-butyl- cyclohexyl) acetate (Verdox ³ ) and 3-[5,5,6-trimethylbicyclo[2.2.1]hept-2-yl]cyclohexan- 1 -ol (Sandela ⁴ ).

Where trade names are given above, these refer to the following sources:

¹ trade name of Symrise GmbH, Germany;

² trade name of BASF SE;

³ trade name of International Flavors & Fragrances Inc., USA;

⁴ Givaudan AG, Switzerland;

⁹ trade name of Firmenich S.A., Switzerland;

¹⁰ trade name of PFW Aroma Chemicals B.V., the Netherlands.

In a preferred embodiment of the invention, the aroma chemicals are selected from the group consisting of methyl benzoate, benzyl acetate, geranyl acetate, 2-isobutyl-4- methyltetrahydro-2H-pyran-4-ol and linalool.

In another preferred embodiment of the invention, the aroma chemicals are selected from the group consisting of ethylvanillin, vanillin, 2,5-dimethyl-4-hydroxy-2H-furan-3- one (furaneol) or 3-hydroxy-2-methyl-4H-pyran-4-one (maltol).

In another preferred embodiment of the invention, the aroma chemicals are selected from the group consisting of geranyl acetate, alpha-hexylcinnamaldehyde, 2-phenoxyethyl isobutyrate, dihydromyrcenol, methyl dihydrojasmonate (preferably with a content of cis isomer of more than 60 wt.%), 4,6,6,7,8,8-hexamethyl-1 , 3, 4, 6,7,8- hexahydrocyclopenta[g]benzopyran, tetrahydrolinalool, ethyllinalool, benzyl salicylate, 2-methyl-3-(4-tert-butylphenyl)propanal, cinnamyl alcohol, 4, 7-methano-3a, 4,5,6,7,7a- hexahydro-5-indenyl acetate, 4,7-methano-3a,4,5,6,7,7a-hexahydro-6-indenyl acetate, citronellyl acetate, tetrahydrogeraniol, linalyl acetate, styrolyl acetate, octahydro-

2.3.8.8-tetramethyl-2-acetonaphthone, 2-acetyl-1 ,2,3,4,6,7,8-octahydro-2,3,8,8- tetramethylnaphthalene, hexyl salicylate, 4-tert-butylcyclohexyl acetate, 2-tert- butylcyclohexyl acetate, alpha-ionone, n-alpha-methylionone, alpha-isomethylionone, coumarin, terpinyl acetate, 4-(4-hydroxy-4-methylpentyl)-3- cyclohexenecarboxaldehyde, alpha-amylcinnamaldehyde, ethylene brassylate, (E)-3- methylcyclopentadec-5-enone, (Z)-3-methylcyclopentadec-5-enone, 15-pentadec-11- enolide, 15-pentadec-12-enolide, 15-cyclopentadecanolide, 1-(5,6,7,8-tetrahydro-

3.5.5.6.8.8-hexamethyl-2-naphthalenyl)ethanone, 2-isobutyl-4-methyltetrahydro- 2H-pyran-4-ol, 2-ethyl-4-(2,2,3-trimethyl-3-cyclopenten-1-yl)-2-buten-1-ol, cis-3-hexenyl acetate, trans-3-hexenyl acetate, trans-2/cis-6-nonadienol, 2,4-dimethyl-3- cyclohexenecarboxaldehyde, 2,4,4,7-tetramethyloct-6-en-3-one, 2,6-dimethyl-5- hepten-1-al, borneol, 3-(3-isopropylphenyl)butanal, 2-methyl-3-(3,4- methylenedioxyphenyl)propanal, 3-(4-ethylphenyl)-2,2-dimethylpropanal, 7-methyl- 2H-1 ,5-benzodioxepin-3(4H)-one, 3,3,5-trimethylcyclohexyl acetate (preferably with a content of cis isomers of 70 wt.% or more), 2,5,5-trimethyl-1 , 2, 3, 4, 4a, 5,6,7- octahydronaphthalen-2-ol, 3-(4-/e/7-butylphenyl)-propanal, ethyl 2-methylpentanoate, ethoxymethoxycyclododecane, 2,4-dimethyl-4,4a,5,9b-tetrahydroindeno[1 ,2- d][1 ,3]dioxine, (2-tert-butylcyclohexyl) acetate, 3-[5,5,6-trimethylbicyclo[2.2.1]hept-2- yl]cyclohexan-1-ol, menthone, isomenthone, carvone, beta-n-methylionone, beta-isomethylionone, alphairone, alpha-damascone, beta-damascone, delta-damascone, acetylated cedar wood oil, and mixtures thereof.

Further useful aroma chemicals different from the 1 ,4-butanediol diesters of the formula (I) can be found, e.g., in S. Arctander, Perfume and Flavor Chemicals, Vol. I and II, Montclair, N. J., 1969, self-published or K. Bauer, D. Garbe and H. Surburg, Common Fragrance and Flavor Materials, 4th Ed., Wiley- VCH, Weinheim 2001. Specifically, mention may be made of: extracts from natural raw materials such as essential oils, concretes, absolutes, resins, resinoids, balsams, tinctures such as e.g. ambergris tincture; amyris oil; angelica seed oil; angelica root oil; aniseed oil; valerian oil; basil oil; tree moss absolute; bay oil; mugwort oil; benzoin resin; bergamot oil; beeswax absolute; birch tar oil; bitter almond oil; savory oil; buchu leaf oil; cabreuva oil; cade oil; calmus oil; camphor oil; cananga oil; cardamom oil; cascarilla oil; cassia oil; cassia absolute; castoreum absolute; cedar leaf oil; cedar wood oil; cistus oil; citronella oil; lemon oil; copaiba balsam; copaiba balsam oil; coriander oil; costus root oil; cumin oil; cypress oil; davana oil; dill weed oil; dill seed oil; Eau de brouts absolute; oak moss absolute; elemi oil; tarragon oil; eucalyptus citriodora oil; eucalyptus oil; fennel oil; pine needle oil; galbanum oil; galbanum resin; geranium oil; grapefruit oil; guaiacwood oil; gurjun balsam; gurjun balsam oil; helichrysum absolute; helichrysum oil; ginger oil; iris root absolute; iris root oil; jasmine absolute; calmus oil; camomile oil blue; roman camomile oil; carrot seed oil; cascarilla oil; pine needle oil; spearmint oil; caraway oil; lab- danum oil; labdanum absolute; labdanum resin; lavandin absolute; lavandin oil; lavender absolute; lavender oil; lemongrass oil; lovage oil; lime oil distilled; lime oil pressed; linalool oil; litsea cubeba oil; laurel leaf oil; mace oil; marjoram oil; mandarin oil; mas- soia bark oil; mimosa absolute; musk seed oil; musk tincture; clary sage oil; nutmeg oil; myrrh absolute; myrrh oil; myrtle oil; clove leaf oil; clove flower oil; neroli oil; olibanum absolute; olibanum oil; opopanax oil; orange blossom absolute; orange oil; origanum oil; palmarosa oil; patchouli oil; peril la oil; peru balsam oil; parsley leaf oil; parsley seed oil; petitgrain oil; peppermint oil; pepper oil; pimento oil; pine oil; pennyroyal oil; rose absolute; rose wood oil; rose oil; rosemary oil; Dalmatian sage oil; Spanish sage oil; sandalwood oil; celery seed oil; spike-lavender oil; star anise oil; styrax oil; tagetes oil; fir needle oil; tea tree oil; turpentine oil; thyme oil; tolubalsam; tonka absolute; tuberose absolute; vanilla extract; violet leaf absolute; verbena oil; vetiver oil; juniper berry oil; wine lees oil; wormwood oil; winter green oil; hyssop oil; civet absolute; cinnamon leaf oil; cinnamon bark oil, and fractions thereof, or ingredients isolated therefrom; individual fragrances from the group of hydrocarbons, such as e.g. 3-carene; alphapinene; beta-pinene; alpha-terpinene; gamma-terpinene; p-cymene; bisabolene; camphene; caryophyllene; cedrene; farnesene; limonene; longifolene; myrcene; ocimene; valencene; (E,Z)-1 ,3,5-undecatriene; styrene; diphenylmethane; the aliphatic alcohols such as e.g. hexanol; octanol; 3-octanol; 2,6-dimethylheptanol; 2-methyl-2-heptanol; 2-methyl-2-octanol; (E)-2-hexenol; (E)- and (Z)-3-hexenol;

1-octen-3-ol; mixture of 3,4,5,6,6-pentamethyl-3/4-hepten-2-ol and 3,5,6,6-tetramethyl- 4-methyleneheptan-2-ol; (E,Z)-2,6-nonadienol; 3,7-dimethyl-7-methoxyoctan-2-ol;

9-decenol; 10-undecenol; 4-methyl-3-decen-5-ol; the aliphatic aldehydes and acetals thereof such as e.g. hexanal; heptanal; octanal; nonanal; decanal; undecanal; dodecanal; tridecanal; 2-methyloctanal;

2-methylnonanal; (E)-2-hexenal; (Z)-4-heptenal; 2,6-dimethyl-5-heptenal;

10-undecenal; (E)-4-decenal; 2-dodecenal; 2,6,10-trimethyl-9-undecenal; 2,6,10-trimethyl-5,9-undecadienal; heptanal diethylacetal; 1 ,1-dimethoxy- 2,2,5-trimethyl-4-hexene; citronellyloxyacetaldehyde; ( E/Z)- 1 -(1 -methoxypropoxy)-hex- 3-ene; the aliphatic ketones and oximes thereof such as e.g. 2-heptanone; 2-octanone; 3-octanone; 2-nonanone; 5-methyl-3-heptanone; 5-methyl-3-heptanone oxime;

2.4.4.7-tetramethyl-6-octen-3-one; 6-methyl-5-hepten-2-one; the aliphatic sulfur-containing compounds such as e.g. 3-methylthiohexanol; 3-methylthiohexyl acetate; 3-mercaptohexanol; 3-mercaptohexyl acetate; 3-mercaptohexyl butyrate; 3-acetylthiohexyl acetate; 1-menthene-8-thiol; the aliphatic nitriles such as e.g. 2-nonenenitrile; 2-undecenenitrile; 2-tridecenenitrile; 3,12-tridecadienenitrile; 3,7-dimethyl-2,6-octadienenitrile; 3,7-dimethyl-6-octenenitrile; the esters of aliphatic carboxylic acids such as e.g. (E)- and (Z)-3-hexenyl formate; ethyl acetoacetate; isoamyl acetate; hexyl acetate; 3, 5, 5-tri methyl hexyl acetate;

3-methyl-2-butenyl acetate; (E)-2-hexenyl acetate; (E)- and (Z)-3-hexenyl acetate; octyl acetate; 3-octyl acetate; 1-octen-3-yl acetate; ethyl butyrate; butyl butyrate; isoamyl butyrate; hexyl butyrate; (E)- and (Z)-3-hexenyl isobutyrate; hexyl crotonate; ethyl isovalerate; ethyl 2-methylpentanoate; ethyl hexanoate; allyl hexanoate; ethyl heptanoate; allyl heptanoate; ethyl octanoate; ethyl (E,Z)-2,4-decadienoate; methyl 2-octinate; methyl 2-noninate; allyl 2-isoamyloxy acetate; methyl-3,7-dimethyl-2,6-octadienoate;

4-methyl-2-pentyl crotonate; the acyclic terpene alcohols such as e.g. geraniol; nerol; linalool; lavandulol; nerolidol; farnesol; tetrahydrolinalool; 2,6-dimethyl-7-octen-2-ol; 2,6-dimethyloctan-2-ol; 2-methyl-

6-methylene-7-octen-2-ol; 2,6-dimethyl-5,7-octadien-2-ol; 2,6-dimethyl-3,5-octadien- 2-ol; 3,7-dimethyl-4,6-octadien-3-ol; 3,7-dimethyl-1 ,5,7-octatrien-3-ol; 2,6-dimethyl-

2.5.7-octatrien-1-ol; and the formates, acetates, propionates, isobutyrates, butyrates, isovalerates, pentanoates, hexanoates, crotonates, tiglinates and 3-methyl- 2-butenoates thereof; the acyclic terpene aldehydes and ketones such as e.g. geranial; neral; citronellal;

7-hydroxy-3,7-dimethyloctanal; 7-methoxy-3,7-dimethyloctanal; 2,6,10-trimethyl- 9-undecenal; geranyl acetone; as well as the dimethyl- and diethylacetals of geranial, neral, 7-hydroxy-3,7-dimethyloctanal; the cyclic terpene alcohols such as e.g. menthol; isopulegol; alpha-terpineol; terpine-4-ol; menthan-8-ol; menthan-1-ol; menthan-7-ol; borneol; isoborneol; linalool oxide; nopol; cedrol; ambrinol; vetiverol; guajol; and the formates, acetates, propionates, isobutyrates, butyrates, isovalerates, pentanoates, hexanoates, crotonates, tiglinates and 3-methyl-2-butenoates thereof; the cyclic terpene aldehydes and ketones such as e.g. menthone; isomenthone; 8-mercaptomenthan-3-one; carvone; camphor; fenchone; alpha-ionone; beta-ionone; alpha-n-methylionone; beta-n-methylionone; alpha-isomethylionone; betaisomethylionone; alpha-irone; alpha-damascone; beta-damascone; beta- damascenone; delta-damascone; gamma-damascone; 1-(2,4,4-trimethyl-2-cyclohexen- 1 -yl)-2-buten-1 -one; 1 ,3,4,6,7,8a-hexahydro-1 , 1 ,5,5-tetramethyl-2H-2,4a-methano- naphthalene-8(5H)-one; 2-methyl-4-(2,6,6-trimethyl-1 -cyclohexen-1 -yl)-2-butenal; noot- katone; dihydronootkatone; 4,6,8-megastigmatrien-3-one; alpha-sinensal; beta- sinensal; acetylated cedar wood oil (methyl cedryl ketone); the cyclic alcohols such as e.g. 4-tert-butylcyclohexanol; 3,3,5-trimethylcyclohexanol;

3-isocamphylcyclohexanol; 2,6,9-trimethyl-Z2,Z5,E9-cyclododecatrien-1-ol; 2-isobutyl-

4-methyltetrahydro-2H-pyran-4-ol; the cycloaliphatic alcohols such as e.g. alpha-3, 3-trimethylcyclohexylmethanol;

1 -(4-isopropylcyclohexyl)ethanol; 2-methyl-4-(2,2,3-trimethyl-3-cyclopent-1 -yl)butanol;

2-methyl-4-(2,2,3-trimethyl-3-cyclopent-1 -yl)-2-buten-1 -ol; 2-ethyl-4-(2,2,3-trimethyl-

3-cyclopent-1-yl)-2-buten-1-ol; 3-methyl-5-(2,2,3-trimethyl-3-cyclopent-1-yl)pentan-2-ol;

3-methyl-5-(2,2,3-trimethyl-3-cyclopent-1-yl)-4-penten-2- ol; 3,3-dimethyl-5-(2,2,3- trimethyl-3-cyclopent-1-yl)-4-penten-2-ol; 1-(2,2,6-trimethylcyclohexyl)pentan-3-ol;

1-(2,2,6-trimethylcyclohexyl)hexan-3-ol; the cyclic and cycloaliphatic ethers such as e.g. cineol; cedryl methyl ether; cyclododecyl methyl ether; 1 ,1 -dimethoxycyclododecane; (ethoxymethoxy)cyclododecane; alpha-cedrene epoxide; 3a,6,6,9a-tetramethyldodecahydronaphtho[2,1-b]furan; 3a- ethyl-6,6,9a-trimethyldodecahydronaphtho[2, 1 -b]furan; 1 ,5,9-trimethyl-13-oxabicyclo- [10.1 ,0]trideca-4,8-diene; rose oxide; 2-(2,4-dimethyl-3-cyclohexen-1-yl)-5-methyl-5-(1- methylpropyl)-1 ,3-dioxane; the cyclic and macrocyclic ketones such as e.g. 4-tert-butylcyclohexanone; 2,2,5-trimethyl-5-pentylcyclopentanone; 2-heptylcyclopentanone; 2-pentylcyclo- pentanone; 2-hydroxy-3-methyl-2-cyclopenten-1 -one; 3-methyl-cis-2-penten-1 -yl-

2-cyclopenten-1 -one; 3-methyl-2-pentyl-2-cyclopenten-1 -one; 3-methyl-4-cyclopenta- decenone; 3-methyl-5-cyclopentadecenone; 3-methylcyclopentadecanone;

4-(1-ethoxyvinyl)-3,3,5,5-tetramethylcyclohexanone; 4-tert-pentylcyclohexanone;

5-cyclohexadecen-1-one; 6,7-dihydro-1 ,1 ,2,3,3-pentamethyl-4(5H)-indanone; 8-cyclo- hexadecen-1-one; 7-cyclohexadecen-1-one; (7/8)-cyclohexadecen-1-one; 9-cyclo- heptadecen-1-one; cyclopentadecanone; cyclohexadecanone; the cycloaliphatic aldehydes such as e.g. 2,4-dimethyl-3-cyclohexenecarbaldehyde;

2-methyl-4-(2,2,6-trimethylcyclohexen-1-yl)-2-butenal; 4-(4-hydroxy-4-methylpentyl)-

3-cyclohexene carbaldehyde; 4-(4-methyl-3-penten-1 -yl)-3-cyclohexenecarbaldehyde; the cycloaliphatic ketones such as e.g. 1-(3,3-dimethylcyclohexyl)-4-penten-1-one;

2.2-dimethyl-1 -(2,4-dimethyl-3-cyclohexen-1 -yl)-1 -propanone; 1 -(5,5-dimethyl-1 -cyclo- hexen-1 -yl)-4-penten-1 -one; 2,3,8,8-tetramethyl-1 ,2,3,4,5,6,7,8-octahydro- 2-naphthalenyl methyl ketone; methyl 2,6,10-trimethyl-2,5,9-cyclododecatrienyl ketone; tert-butyl (2,4-dimethyl-3-cyclohexen-1-yl) ketone; the esters of cyclic alcohols such as e.g. 2-tert-butylcyclohexyl acetate; 4-tert- butylcyclohexyl acetate; 2-tert-pentylcyclohexyl acetate; 4-tert-pentylcyclohexyl acetate; 3,3,5-trimethylcyclohexyl acetate; decahydro-2-naphthyl acetate;

2-cyclopentylcyclopentyl crotonate; 3-pentyltetrahydro-2H-pyran-4-yl acetate; decahy- dro-2,5,5,8a-tetramethyl-2-naphthyl acetate; 4,7-methano-3a,4,5,6,7,7a-hexahydro-5 or 6-indenyl acetate; 4,7-methano-3a,4,5,6,7,7a-hexahydro-5 or 6-indenyl propionate;

4.7-methano-3a,4,5,6,7,7a-hexahydro-5 or 6-indenyl isobutyrate;

4.7-methanooctahydro-5 or 6-indenyl acetate; the esters of cycloaliphatic alcohols such as e.g. 1 -cyclohexylethyl crotonate; the esters of cycloaliphatic carboxylic acids such as e.g. allyl 3-cyclohexyl propionate; allyl cyclohexyloxyacetate; cis- and trans-methyl dihydrojasmonate; cis- and transmethyl jasmonate; methyl 2-hexyl-3-oxocyclopentanecarboxylate; ethyl 2-ethyl- 6,6-dimethyl-2-cyclohexenecarboxylate; ethyl 2,3,6,6-tetramethyl-2-cyclohexene- carboxylate; ethyl 2-methyl-1 ,3-dioxolane-2-acetate; the araliphatic alcohols such as e.g. benzyl alcohol; 1 -phenylethyl alcohol, 2-phenylethyl alcohol, 3-phenylpropanol; 2-phenylpropanol; 2-phenoxyethanol;

2.2-dimethyl-3-phenylpropanol; 2,2-dimethyl-3-(3-methylphenyl)propanol; 1 ,1-dimethyl- 2-phenylethyl alcohol; 1 ,1-dimethyl-3-phenylpropanol; 1-ethyl-1-methyl-3- phenylpropanol; 2-methyl-5-phenylpentanol; 3-methyl-5-phenylpentanol; 3-phenyl-2- propen-1-ol; 4-methoxybenzyl alcohol; 1-(4-isopropylphenyl)ethanol; the esters of araliphatic alcohols and aliphatic carboxylic acids such as e.g. benzyl acetate; benzyl propionate; benzyl isobutyrate; benzyl isovalerate; 2-phenylethyl acetate; 2-phenylethyl propionate; 2-phenylethyl isobutyrate; 2-phenylethyl isovalerate;

1 -phenylethyl acetate; alpha-trichloromethylbenzyl acetate; alpha, alpha-dimethyl- phenylethyl acetate; alpha, alpha-dimethylphenylethyl butyrate; cinnamyl acetate;

2-phenoxyethyl isobutyrate; 4-methoxybenzyl acetate; the araliphatic ethers such as e.g. 2-phenylethyl methyl ether; 2-phenylethyl isoamyl ether; 2-phenylethyl 1 -ethoxyethyl ether; phenylacetaldehyde dimethyl acetal; phenylacetaldehyde diethyl acetal; hydratropaaldehyde dimethyl acetal; phenylacetaldehyde glycerol acetal; 2,4,6-trimethyl-4-phenyl-1 ,3-dioxane; 4,4a,5,9b-tetrahydroindeno[1 ,2- d]-m-dioxine; 4,4a,5,9b-tetrahydro-2,4-dimethylindeno[1 ,2-d]-m-dioxine; the aromatic and araliphatic aldehydes such as e.g. benzaldehyde; phenylacetaldehyde; 3-phenylpropanal; hydratropaaldehyde; 4-methylbenzaldehyde;

4-methylphenylacetaldehyde; 3-(4-ethylphenyl)-2,2-dimethylpropanal; 2-methyl-3-(4- isopropylphenyl)propanal; 2-methyl-3-(4-tert-butylphenyl)propanal; 2-methyl-3-(4- isobutylphenyl)propanal; 3-(4-tert-butylphenyl)propanal; cinnamaldehyde; alpha- butylcinnamaldehyde; alpha-amylcinnamaldehyde; alpha-hexylcinnamaldehyde;

3-methyl-5-phenylpentanal; 4-methoxybenzaldehyde; 4-hydroxy-3-methoxy- benzaldehyde; 4-hydroxy-3-ethoxybenzaldehyde; 3,4-methylenedioxybenzaldehyde; 3,4-dimethoxybenzaldehyde; 2-methyl-3-(4-methoxyphenyl)propanal; 2-methyl-3-(4- methylenedioxyphenyl)propanal; the aromatic and araliphatic ketones such as e.g. acetophenone;

4-methylacetophenone; 4-methoxyacetophenone; 4-tert-butyl-2,6-dimethylaceto- phenone; 4-phenyl-2-butanone; 4-(4-hydroxyphenyl)-2-butanone; 1-(2-naphthalenyl)- ethanone; 2-benzofuranylethanone; (3-methyl-2-benzofuranyl)ethanone; benzophenone; 1 ,1 ,2,3,3,6-hexamethyl-5-indanyl methyl ketone; 6-tert-butyl-1 ,1-dimethyl-

4-indanyl methyl ketone; 1-[2,3-dihydro-1 ,1 ,2,6-tetramethyl-3-(1-methylethyl)-1 H-

5-indenyl]ethanone; 5',6',7',8'-tetrahydro-3',5',5',6',8',8'-hexamethyl-2-aceton aphthone; the aromatic and araliphatic carboxylic acids and esters thereof such as e.g. benzoic acid; phenylacetic acid; methyl benzoate; ethyl benzoate; hexyl benzoate; benzyl benzoate; methyl phenylacetate; ethyl phenylacetate; geranyl phenylacetate; phenylethyl phenylacetate; methyl cinnamate; ethyl cinnamate; benzyl cinnamate; phenylethyl cinnamate; cinnamyl cinnamate; allyl phenoxyacetate; methyl salicylate; isoamyl salicylate; hexyl salicylate; cyclohexyl salicylate; cis-3-hexenyl salicylate; benzyl salicylate; phenylethyl salicylate; methyl 2,4-dihydroxy-3,6-dimethylbenzoate; ethyl 3- phenylglycidate; ethyl 3-methyl-3-phenylglycidate; the nitrogen-containing aromatic compounds such as e.g. 2,4,6-trinitro-1 ,3-dimethyl- 5-tert-butylbenzene; 3,5-dinitro-2,6-dimethyl-4-tert-butylacetophenone; cinnamonitrile;

3-methyl-5-phenyl-2-pentenonitrile; 3-methyl-5-phenylpentanonitrile; methyl anthranil- ate; methyl-N-methylanthranilate; Schiff bases of methyl anthranilate with 7-hydroxy- 3,7-dimethyloctanal, 2-methyl-3-(4-tert-butylphenyl)propanal or 2,4-dimethyl-3- cyclohexenecarbaldehyde; 6-isopropylquinoline; 6-isobutylquinoline; 6-sec- butylquinoline; 2-(3-phenylpropyl)pyridine; indole; skatole; 2-methoxy-3-isopropyl- pyrazine; 2-isobutyl-3-methoxypyrazine; the phenols, phenyl ethers and phenyl esters such as e.g. estragole; anethole; eugenol; eugenyl methyl ether; isoeugenol; isoeugenyl methyl ether; thymol; carvacrol; diphenyl ether; beta-naphthyl methyl ether; beta-naphthyl ethyl ether; beta-naphthyl isobutyl ether; 1 ,4-dimethoxybenzene; eugenyl acetate; 2-methoxy-4-methylphenol; 2-ethoxy-5-(1-propenyl)phenol; p-cresyl phenylacetate; the heterocyclic compounds such as e.g. 2,5-dimethyl-4-hydroxy-2H-furan-3-one; 2-ethyl-4-hydroxy-5-methyl-2H-furan-3-one; 3-hydroxy-2-methyl-4H-pyran-4-one; 2-ethyl-3-hydroxy-4H-pyran-4-one; the lactones such as e.g. 1 ,4-octanolide; 3-methyl-1 ,4-octanolide; 1 ,4-nonanolide;

1 .4-decanolide; 8-decen-1 ,4-olide; 1 ,4-undecanolide; 1 ,4-dodecanolide;

1 .5-decanolide; 1 ,5-dodecanolide; 4-methyl-1 ,4-decanolide; 1 ,15-pentadecanolide; cisand trans-11-pentadecen-1 , 15-olide; cis- and trans-12-pentadecen-1 , 15-olide;

1 ,16-hexadecanolide; 9-hexadecen-1 , 16-olide; 10-oxa-1 ,16-hexadecanolide; 11-oxa- 1 ,16-hexadecanolide; 12-oxa-1 ,16-hexadecanolide; ethylene 1 ,12-dodecanedioate; ethylene 1 ,13-tridecanedioate; coumarin; 2,3-dihydrocoumarin; octahydrocoumarin.

More preferably, the aroma chemicals different from the 1 ,4-butanediol diesters of the formula (I) comprise one or more of the following aroma chemicals: geranyl acetate, alpha-hexylcinnamaldehyde, 2-phenoxyethyl isobutyrate, dihydromyrcenol, methyl di- hydrojasmonate (preferably with a content of cis isomer of more than 60 wt.%), 4,6,6,7,8,8-hexamethyl-1 ,3,4,6,7,8-hexahydrocyclopenta[g]benzopyran, tetrahydrolinalool, ethyllinalool, benzyl salicylate, 2-methyl-3-(4-tert-butylphenyl)propanal, cin- namyl alcohol, 4,7-methano-3a,4,5,6,7,7a-hexahydro-5-indenyl acetate, 4,7-methano- 3a,4,5,6,7,7a-hexahydro-6-indenyl acetate, citronellol, citronellyl acetate, tetrahydrogeraniol, vanillin, linalyl acetate, styrolyl acetate, octahydro-2, 3,8, 8-tetramethyl-2- acetonaphthone, 2-acetyl-1 ,2,3,4,6,7,8-octahydro-2,3,8,8-tetramethylnaphthalene, hexyl salicylate, 4-tert-butylcyclohexyl acetate, 2-tert-butylcyclohexyl acetate, alphaionone, n-alpha-methylionone, alpha-isomethylionone, coumarin, terpinyl acetate, 2-phenylethyl alcohol, 4-(4-hydroxy-4-methylpentyl)-3-cyclohexenecarboxaldehyde, alpha-amylcinnamaldehyde, ethylene brassylate, (E)-3-methylcyclopentadec-5-enone, (Z)-3-methylcyclopentadec-5-enone, 15-pentadec-11 -enolide, 15-pentadec-12-enolide, 15-cyclopentadecanolide, 1 -(5,6,7,8-tetrahydro-3,5,5,6,8,8-hexamethyl-2- naphthalenyl)ethanone, 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol, 2-ethyl-4-(2,2,3- trimethyl-3-cyclopenten-1-yl)-2-buten-1-ol, cis-3-hexenyl acetate, trans-3-hexenyl acetate, trans-2/cis-6-nonadienol, 2,4-dimethyl-3-cyclohexenecarboxaldehyde, 2, 4,4,7- tetramethyloct-6-en-3-one, 2,6-dimethyl-5-hepten-1-al, borneol, 3-(3-isopropylphenyl)butanal, 2-methyl-3-(3,4-methylenedioxyphenyl)propanal, 3-(4- ethylphenyl)-2,2-dimethylpropanal, 7-methyl-2H-1 ,5-benzodioxepin-3(4H)-one, 3,3,5- trimethylcyclohexyl acetate (preferably with a content of cis isomers of 70 wt.% or more), 2,5,5-trimethyl-1 ,2,3,4,4a,5,6,7-octahydronaphthalen-2-ol, 3-(4-/e/7-butylphenyl)- propanal, ethyl 2-methylpentanoate, ethoxymethoxycyclododecane, 2,4-dimethyl- 4,4a,5,9b-tetrahydroindeno[1 ,2-d][1 ,3]dioxine, (2-tert-butylcyclohexyl) acetate, 3-[5,5,6- trimethylbicyclo[2.2.1]hept-2-yl]cyclohexan-1-ol, menthone, isomenthone, carvone, camphor, beta-ionone, beta-n-methylionone, betaisomethylionone, alpha-irone, alpha-damascone, beta-damascone, beta- damascenone, delta-damascone, acetylated cedar wood oil, ambergris tincture, bergamot oil, cedar wood oil, lemon oil, davana oil, ginger oil, la- vandin absolute, lavandin oil, lavender absolute, lavender oil, lime oil distilled, lime oil pressed, mandarin oil, clary sage oil, orange blossom absolute, orange oil, patchouli oil, pepper oil, vetiver oil; (E)- and (Z)-3-hexenol, 4-methyl-3-decen-5-ol, 2-dodecenal, 1 ,1-dimethoxy-2,2,5-trimethyl-4-hexene, 3,7-dimethyl-6-octenenitrile, ethyl acetoacetate, isoamyl acetate, hexyl acetate, isoamyl butyrate, hexyl butyrate, (E)- and (Z)-3- hexenyl isobutyrate, ethyl 2-methylpentanoate, ethyl hexanoate, allyl hexanoate, ethyl (E,Z)-2,4-decadienoate, geraniol, nerol, linalool, geranyl propionate, geranyl butyrate, geranial, neral, nootkatone, 3-methyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)-pentan-2-ol,

3.3-dimethyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)-4-pen ten-2-ol, cedryl methyl ether, 3a,6,6,9a-tetramethyldodecahydronaphtho[2,1-b]furan, rose oxide, 6,7-dihydro-

1 .1 .2.3.3-pentamethyl-4(5H)-indanone, 1 -(5,5-dimethyl-1 -cyclohexen-1 -yl)-4-penten-1 - one, 4,7-methano-3a,4,5,6,7,7a-hexahydro-5- or 6-indenyl propionate, 4,7- methanooctahydro-5- or 6-indenyl acetate, allyl 3-cyclohexylpropionate, 1 -phenylethyl alcohol, benzyl acetate, 1 -phenylethyl acetate, alpha, alpha--dimethylphenylethyl acetate, alpha, alpha-dimethylphenylethyl butyrate, 2,4,6-trimethyl-4-phenyl-1 ,3-dioxane, 2- methyl-3-(4-isopropylphenyl)-propanal, cinnamaldehyde, 4-(4-hydroxyphenyl)-2- butanone, phenylethyl phenylacetate, ethyl 3-methyl-3-phenylglycidate, estragole, anethole, eugenol, 3-hydroxy-2-methyl-4H-pyran-4-one, 2-ethyl-3-hydroxy-4H-pyran-4-one, 1 ,4-decanolide, 1 ,4-undecanolide, 1 ,15-pentadecanolide, coumarin. In another preferred embodiment, the aroma chemicals different from the 1 ,4- butanediol diesters of the formula (I) comprise one or more of the following aroma chemicals:

Aldehyde C-08, Aldehyde C-09, Aldehyde C-10, Aldehyde C-14 (undecalactone), Aldehyde C-16, Allyl amyl glycolate, Allyl caproate, Allyl cyclohexane propionate, Allyl heptylate, Ambrocenide, Ambroxan, Amyl butyrate, Anisic aldehyde, Benzaldehyde, Benzyl acetate, Benzyl salicylate, Bergamot oil, Calone, Cashmeran, Cedarwood oil, Cedramber, Cinnamic aldehyde, Citral, Citronellal, Citronellol, Citronelyl nitrile, Clary Sage oil, Coriander oil, Coumarin, Cyclacet, Cyclamen aldehyde, Damascenone, Damascene alpha, Davana oil, Decalactone gamma, Dihydromyrcenol, Dimethyl benzyl carbinyl acetate, Diphenyl oxide, trans-2-dodecenal, Ethyl acetoacetate, Ethylene glycol brasylate, Ethyl linalool, Ethyl-2-methyl butyrate, Ethyl vanillin, Eugenol, Evernyl, Floralozone, Florhydral, Galaxolide, Galbascone, Geraniol, Geranyl acetate, Grapefruit oil, Habanolide, Hedione, Heliotropine, Helvetolide, cis-3-Hexenol, cis-3-Hexenyl acetate, cis-3-Hexenyl isobutyrate, Hexyl acetate, Hexyl cinnamic aldehyde, Hexyl salicylate, Indolarome, beta-lonone, Isobornyl acetate, Isocyclocitral, Iso E super, Isomenthone, Lactone C-12 gamma, Lavandin oil, Lavender oil, Lemon oil, Liffarome, Ligus- tral, Linalool, Linalyl acetate, Mandarin oil, Manzanate, Melonal, Methyl anthranilate, Methyl benzoate, Methyl ionone, gamma-Methyl ionone, Methyl pamplemousse, Nopyl acetate, Olibanum resinoid, Oxane, Patchouli oil, Pepper oil, Petitgrain oil, Phenoxyethyl isobutyrate, Phenylethyl alcohol, PTBCHA (p-tert-butylcyclohexyl acetate), Prenyl acetate, Pyranol, Pyranyl acetate, Raspberry ketone, Rosemary oil, Rose oxide, Saf- ranolide, Sandalore, Styrallyl acetate, Styryl acetate, Terpineol, Terpenyl acetate, Tetrahydrolinalool, Thiomenthone, Tonalid, Triplal, Undecavertol, Vanillin, Verdox, Vertofix, Vetivert oil.

The mixture of the 1 ,4-butanediol diesters of the formula (I) and the one or more aroma chemicals different therefrom or the resulting composition containing the 1 ,4-butanediol diesters of the formula (I) and the one or more aroma chemicals different therefrom as obtained in method C can be or can be used in a wide range of compositions, preferably can be/can be used in an aroma composition, more preferably can be/can be used in a fragrance composition. The olfactory properties and the substance properties (such as solubility in customary solvents and compatibility with further customary constituents of such compositions) of the compounds (I) underline the particular suitability of the combinations for the stated use purposes and compositions.

Suitable compositions are for example perfume compositions, body care compositions (including cosmetic compositions), products for oral and dental hygiene, hygiene articles, cleaning compositions (including dishwashing compositions), textile detergent compositions, compositions for scent dispensers, foods, food supplements, pharmaceutical compositions and crop protection compositions.

To be clear, the 1 ,4-butanediol diesters serve for providing a pleasant aroma (especially fragrance) to said compositions, and not as pharmaceutical, crop protectant, food, or the like.

Perfume compositions can be selected from fine fragrances, air fresheners in liquid form, gel-like form or a form applied to a solid carrier, aerosol sprays, scented cleaners, perfume candles and oils, such as lamp oils or oils for massage.

Examples for fine fragrances are perfume extracts, Eau de Parfums, Eau de Toilettes, Eau de Colognes, Eau de Solide and Extrait Parfum.

Body care compositions include cosmetic compositions, and can be selected from after-shaves, pre-shave products, splash colognes, solid and liquid soaps, shower gels, shampoos, shaving soaps, shaving foams, bath oils, cosmetic emulsions of the oil-in- water type, of the water-in-oil type and of the water-in-oil-in-water type, such as e.g. skin creams and lotions, face creams and lotions, sunscreen creams and lotions, aftersun creams and lotions, hand creams and lotions, foot creams and lotions, hair removal creams and lotions, after-shave creams and lotions, tanning creams and lotions, hair care products such as e.g. hairsprays, hair gels, setting hair lotions, hair conditioners, hair shampoo, permanent and semi-permanent hair colorants, hair shaping compositions such as cold waves and hair smoothing compositions, hair tonics, hair creams and hair lotions, deodorants and antiperspirants such as e.g. underarm sprays, rollons, deodorant sticks and deodorant creams, products of decorative cosmetics such as e.g. eye-liners, eye-shadows, nail varnishes, make-ups, lipsticks and mascara. Further examples are given above.

Products for oral and dental hygiene can be selected from toothpaste, dental floss, mouth wash, breath fresheners, dental foam, dental gels and dental strips.

Hygiene articles can be selected from joss sticks, insecticides, repellents, propellants, rust removers, perfumed freshening wipes, armpit pads, baby diapers, sanitary towels, toilet paper, cosmetic wipes, pocket tissues, dishwasher and deodorizer.

Cleaning compositions, such as e.g. cleaners for solid surfaces, can be selected from perfumed acidic, alkaline and neutral cleaners, such as e.g. floor cleaners, window cleaners, dishwashing compositions both for handwashing and machine washing use, bath and sanitary cleaners, scouring milk, solid and liquid toilet cleaners, powder and foam carpet cleaners, waxes and polishes such as furniture polishes, floor waxes, shoe creams, disinfectants, surface disinfectants and sanitary cleaners, brake cleaners, pipe cleaners, limescale removers, grill and oven cleaners, algae and moss removers, mold removers, facade cleaners.

Textile detergent compositions can be selected from liquid detergents, powder detergents, laundry pretreatments such as bleaches, soaking agents and stain removers, fabric softeners, washing soaps, washing tablets.

Food means a raw, cooked, or processed edible substance, ice, beverage or ingredient used or intended for use in whole or in part for human consumption, or chewing gum, gummies, jellies, and confectionaries.

A food supplement is a product intended for ingestion that contains a dietary ingredient intended to add further nutritional value to the diet. A dietary ingredient may be one, or any combination, of the following substances: a vitamin, a mineral, an herb or other botanical, an amino acid, a dietary substance for use by people to supplement the diet by increasing the total dietary intake, a concentrate, metabolite, constituent, or extract. Food supplements may be found in many forms such as tablets, capsules, softgels, gelcaps, liquids, or powders.

Pharmaceutical compositions comprise compositions which are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease as well as articles (other than food) intended to affect the structure or any function of the body of man or other animals.

Crop protection compositions comprise compositions which are intended for the managing of plant diseases, weeds and other pests (both vertebrate and invertebrate) that damage agricultural crops and forestry.

Preferably, the mixture or composition resulting in method C is to be used in or is a perfume composition, a body care composition (including cosmetic compositions), a product for oral and dental hygiene, a hygiene article, a cleaning composition (including dishwashing compositions), a textile detergent composition, a composition for scent dispensers, or a crop protection composition.

In particular, the mixture or composition resulting in method C is to be used in or is a personal care or a homecare composition, such as a body care composition (including cosmetic compositions), a cleaning composition (including dishwashing compositions), a textile detergent composition or an air care composition.

Generally, the total amount of the 1 ,4-butanediol diesters of the formula (I) in the mix- ture/compositions resulting in method C is typically adapted to the particular intended use or the intended application and can, thus, vary over a wide range. As a rule, the customary standard commercial amounts for scents are used.

The mixture/compositions resulting in method C can comprise the compounds of formula (I) in an overall amount of from 0.001 to 99.9% by weight, preferably from 0.005 to 90% by weight, more preferably from 0.008 to 80%, in particular from 0.01 to 60% by weight, more particularly from 0.01 to 40% by weight, e.g. from 0.01 to 20% by weight or 0.01 to 10% by weight or 0.01 to 5% by weight or 0.05 to 5% by weight, based on the total weight of the composition.

In one embodiment of the invention, the mixture/compositions resulting in method C comprises the compounds of formula (I) in an overall amount of from 0.001 to 20 weight% or from 0.005 to 20 weight%, preferably from 0.01 to 20 weight% or from 0.01 to 10 weight%, based on the total weight of the composition.

The methods of the invention allow the simple preparation of ester compounds (I) in satisfactory yields and avoids the formation of tetrahydrofuran as side product. The methods can be carried out with starting materials of renewable origin and thus produce the desired compounds (I) with a reduced CO2 footprint. Aroma chemical compositions with a reduced content of tetrahydrofuran are obtainable without tedious purification steps.

The invention is now illustrated by the following examples.

EXAMPLES

GC analyses were performed using an Agilent 7890 A equipped with a Rxi-1 MS 30m column (30 m, 0.32 mm, 0.5 pm).

Temperature program: 60 °C

6 K/min to 250 °C

Constant Flow: 1 .7 ml/min

Carrier gas: Hydrogen

Injector temperature: 250°C Detector temperature: 280°C GC-a% means area of the respective signal in the gas chromatogram.

A. Synthesis

Example 1 :

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid without catalyst and without entrainer

In a 250 mL flask equipped with reflux condenser, 1 ,4-butanediol (45.1 g, 0.50 mol, 1 .00 equiv.) and acetic acid (90.1 g, 1.50 mol, 3 equiv.) were stirred and heated to reflux (120-115°C; temperature decreasing in the course of the formation of water) for 23 hours to yield a mixture of acetic acid (20.5 GC-a%), 1 ,4-butanediol (2.08 GC-a%), 1- acetoxy-4-hydroxybutane (22.6 GC-a%) and 1 ,4-diacetoxybutane (53.3 GC-a%). Formation of tetrahydrofuran was not observed.

Comparative example 1 :

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid with catalyst (amberlyst) and without entrainer

In a 250 mL flask equipped with reflux condenser, 1 ,4-butanediol (45.1 g, 0.50 mol, 1.00 equiv.), acetic acid (90.1 g, 1.50 mol, 3 equiv.) and amberlyst 15(H) ion exchange resin (0.450 g) were stirred and heated to reflux (120-109°C temperature decreasing in the course of the formation of water) for 23 hours to yield a mixture of acetic acid (23.4 GC-a%), tetrahydrofuran (3.22 GC-a%), 1 ,4-butanediol (1.40 GC-a%), 1-acetoxy-4- hydroxybutane (20.1 GC-a%) and 1 ,4-diacetoxybutane (51.9 GC-a%).

Example 2:

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid without catalyst and with entrainer

In a 250 mL flask equipped with a Dean-Stark apparatus that is filled with isopropyl acetate (entrainer), 1 ,4-butanediol (45.1 g, 0.50 mol, 1.00 equiv.), acetic acid (90.1 g, 1 .50 mol, 3 equiv.) and isopropyl acetate (16.8 g, 0.165 mol, 0.33 equiv.) were stirred and heated to reflux (115-126°C; temperature increase in the course of the removal of water with entrainer) for 23 hours to yield a mixture of acetic acid (13.8 GC-a%), isopropyl acetate (14.4 GC-a%), 1-acetoxy-4-hydroxybutane (2.60 GC-a%) and 1 ,4- diacetoxybutane (69.2 GC-a%). Formation of tetrahydrofuran was not observed. Comparative example 2:

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid with catalyst (amberlyst) and with entrainer

In a 250 mL flask equipped with a Dean-Stark apparatus that is filled with isopropyl acetate, 1 ,4-butanediol (45.1 g, 0.50 mol, 1.00 equiv.), acetic acid (90.1 g, 1.50 mol, 3 equiv.), amberlyst 15(H) ion exchange resin (0.450 g) and isopropyl acetate (16.8 g, 0.165 mol, 0.33 equiv.) were stirred and heated to reflux (115-126°C; temperature increase in the course of the removal of water with entrainer) for 23 hours to yield a mixture of acetic acid (22.4 GC-a%), tetra hydrofuran (1.81 GC-a%), isopropyl acetate (5.53 GC-a%) and 1 ,4-diacetoxybutane (70.3 GC-a%) and other light volatiles. Additional THF and other light volatiles were found in the Dean-Stark trap.

Comparative example 3:

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid with catalyst (sulfuric acid) and with entrainer

In a 250 mL flask equipped with a Dean-Stark apparatus that is filled with isopropyl acetate, 1 ,4-butanediol (45.1 g, 0.50 mol, 1.00 equiv.), acetic acid (90.1 g, 1.50 mol, 3 equiv.), sulfuric acid (0.49 g, 5.00 mmol, 0.01 equiv.) and isopropyl acetate (16.8 g, 0.165 mol, 0.33 equiv.) were stirred and heated to reflux (106-126°C°; temperature increase in the course of the removal of water with entrainer) for 7 hours. Prior to analysis, a sample was diluted in ethyl acetate and treated with solid sodium hydrogencarbonate. After this treatment the mixture contained acetic acid (13.7 GC-a%), tetrahydrofuran (1.10 GC-a%), isopropylacetate (15.8 GC-a%), 1-acetoxy-4-hydroxybutane (0.87 GC-a%) and 1 ,4-diacetoxybutane (68.5 GC-a%) and other light volatiles. Additional THF and other light volatiles were found in the Dean-Stark trap.

For a better overview, the results are compiled in Table 1 .

Table 1. Reaction of 1 ,4-butanediol (1.00 equiv.) with acetic acid (3.00 equiv.) at reflux ^a > Additional THF and other light volatiles were found in the Dean-Stark trap. I PA isopropyl acetate

BDO 1 ,4-butanediol

BDOMA 1-acetoxy-4-hydroxybutane; 1 ,4-butanediol monoacetate

BDODA 1 ,4-diacetoxybutane; 1 ,4-butanediol diacetate

As the results show, examples 1 and 2 according to the invention and comparative examples Comp-1 , Comp-2 and Comp-3 using acidic catalysts surprisingly afford the desired 1 ,4-diacetoxybutane in comparable yields. In the comparative examples, THF is formed as side product, whereas in examples 1 and 2 according to the invention no THF could be detected.

Example 3:

Preparation of 1 ,4-diacetoxybutane (compound (I) wherein R ¹ is CH3) by reaction of 1 ,4-butanediol with acetic acid and subsequently with acetic anhydride without catalyst and without entrainer

In a 2.5 L flask equipped with a reflux condenser, a starting mixture of 1 ,4-butanediol (676 g; 7.51 mol; 1 equiv.) and acetic acid (1 .35 kg; 22.5 mol; (3 equiv.) was stirred and heated to reflux at 121-114°C (temperature decreasing in the course of the formation of water) for 5 hours; then water formed in the reaction was removed by evaporation at 114-145 °C for 180 minutes. The reaction product contained acetic acid (22.8% by weight), 1 ,4-butanediol (1.64% by weight), 1 -acetoxy-4-hydroxybutane (20.6% by weight) and 1 ,4-diacetoxybutane (58.4% by weight) according to GC analysis.

Then acetanhydride (334 g; 3.27 mol; 0.43 equiv.) was added within 80 min and the reaction mixture was heated for another 3 hours at 135 to 137°C to yield a mixture of acetic acid (30.6% by weight), 1-acetoxy-4-hydroxybutane (1.2% by weight) and 1 ,4- diacetoxybutane (68.2% by weight). Formation of tetrahydrofuran was not observed.

B. Preparation of aroma chemical compositions

I. Isolation of 1 ,4-diacetoxybutane

The reaction product of example 1 was distilled at 3 mbar and 94°C.

The product contained 0.3% of the monoester (1-acetoxy-4-hydroxybutane) and 99.6% of the diester (1 ,4-diacetoxybutane) (GC area).

IL Advantageous fragrance compositions

11.1 Perfume formulation for various uses A base formulation of the composition listed in the following table was prepared by mixing the components. DPG is dipropylene glycol.

T o this base formulation 2.5% by weight of the product of example I was added and thoroughly mixed. The resulting perfume formulation was olfactively evaluated as follows by a panel of trained perfumers: The product of example I adds an own impression and signature to the base formulation, conferring to the perfume formulation a red fruit note and making it nicer, stronger, more natural, powerful and greener. 11.2 Perfume formulation for various uses

A base formulation of the composition listed in the following table was prepared by mixing the components. DPG is dipropylene glycol. This base formulation had a green, light fruity, slightly tropical sweet, floral of jasmine and rose scent with woody, musky backnotes.

To this base formulation, 100 parts by weight of the product of example I were added and thoroughly mixed. The resulting perfume formulation was characterized by a panel of trained perfumers as more fruity and sweet, more raspberry, moreover the musk note was more pronounced. The product of example I thus also acts as a booster for musk notes. II.3 Perfume formulation intended for use in dishwashing formulations

A base formulation of the composition listed in the following table for use in dishwashing formulations was prepared by mixing the components.

T o this base formulation 500 parts by weight of the product of example I was added and thoroughly mixed. The resulting perfume formulation was olfactively evaluated as follows by a panel of trained perfumers:

The product of example I adds a red fruit, strawberry, sweet note to the base formulation.

11.4 Perfume formulation intended for use in reed diffusers

A formulation of the composition listed in the following table for use in reed diffusers (scent dispenser where the scent is dispensed by slow evaporation supported by reeds) was prepared by mixing the components.

The resulting perfume formulation was olfactively evaluated by a panel of trained perfumers as sweeter, more fruity than without the product of example I. 11.5 Perfume formulation intended for use in shower gel A base formulation of the composition listed in the following table for use in shower gels was prepared by mixing the components. The resulting perfume formulation was olfactively evaluated by a panel of trained perfumers as a tropical fruit blend with multiple fruit notes including watermelon, kiwi, pineapple, passionfruit and grapefruit on a floral, musky base. An analogous formulation was prepared, containing however 50 parts by weight of DPG instead of the product of example I. This was characterized as a bright, fresh tropical fruit blend with obvious notes of watermelon and floral musky undertones.

A comparison of the two blends revealed that the product of example I introduces a more natural effect and multiplies the various tropical notes, especially in the direction of pineapple. Watermelon remains, but it is better outbalanced, other fruits becoming better perceivable. The product of example I thus also acts as a booster for certain notes. 11.6 Perfume formulation intended for use in shower gel

A base formulation of the composition listed in the following table for use in shower gels was prepared by mixing the components.

The resulting perfume formulation was olfactively evaluated by a panel of trained perfumers as a fresh, bright lavender fragrance with a dominant natural impression in a modern context provided by woody, musky and citrus elements.

An analogous formulation was prepared, containing however 50 parts by weight of DPG instead of the product of example I. This was characterized as a classical lavender fragrance modernized with Dihydro myrcenol and Iso E Super and having a fresh citrus accord in the topnotes.

A comparison of the two blends revealed that the product of example I energizes the topnotes and delivers a more natural feel by virtue of its fruity notes which emphasize the ketonic notes of the lavandin and lavender.

III. Ready-to-use compositions

111.1 Shampoo or shower gel

A shampoo or shower gel formulation was prepared by mixing the following components in the given proportions:

The shower/shampoo formulation had a pleasant fruity fragrance of the notes listed in example 11.5. The analogous formulation containing 1 % of the perfume composition from example

II.6 instead of the perfume composition from example II.5 had a pleasant lavender fragrance of the notes listed in example 11.6.

The analogous formulation containing 0.1 % of 1 ,4-butanediol diacetate of example I instead of the perfume composition from example 11.5 covered the unpleasant odor of the base formulation (i.e. above shampoo or shower gel formulation without perfume) well. The formulation containing 0.1 % of 1 ,4-butanediol diacetate of example I instead of the perfume composition from example 11.5 had a distinctive fruity scent. III.2 Laundry detergent formulation

A laundry detergent formulation was prepared by mixing the following components in the given proportions:

The resulting clear and slightly yellowish formulation of a pH of 8.1 had a pleasant fruity fragrance of the notes listed in example 11.1. The analogous formulation containing 0.5% of 1 ,4-butanediol diacetate of example I instead of the perfume composition from example 11.1 covered the unpleasant odor of the base formulation (i.e. above laundry detergent formulation without perfume) well. Increasing the amount of 1 ,4-butanediol diacetate of example I (but still below 1 %) led to a distinctive fruity scent.