Branched adipic acid based esters as novel base stocks and lubricants

Field of the Invention

The presently claimed invention is directed to the use of branched adipic acid esters as lubri- cants as well as lubricant compositions containing the branched adipic acid esters.

Background of the Invention

In the recent years, the efficiencies of automotive engines have increased significantly in order to conserve fuel and to comply with statutory and regulatory requirements on automotive fuel consumption. This increased efficiency has, in turn, led to more severe service requirements for the engine lubricants because the higher efficiencies have generally been accompanied by higher engine temperatures as well as higher bearing pressures concomitant upon the use of higher compression ratios. These increasingly severe service requirements have made it nec- essary for lubricant manufacturers to provide superior lubricants.

The commercially available lubricant compositions are produced from a multitude of different natural or synthetic components. To improve the desired properties further additives are usually added according to the field of use. The base oils often consist of mineral oils, highly refined mineral oils, alkylated mineral oils, poly-alpha-olefins (PAOs), polyalkylene glycols, phosphate esters, silicone oils, diesters and esters of polyhydric alcohols.

The different lubricants, such as motor oil, turbine oil, hydraulic fluid, transmission oil, compres- sor oil and the like, must satisfy extremely high criteria such as high viscosity index, good lubri- cant performance, high oxidation stability, good thermal stability or comparable properties.

High-performance lubricant oil formulations which are used as transmission, industrial or motor oils are oils featuring a special performance profile with regard to shear stability, low- temperature viscosity, long service life, evaporation loss, fuel efficiency, seal compatibility and wear protection. Such oils are currently being formulated preferentially with PAO (especially PAO 6) or Group I, Group II or Group III mineral oils as carrier fluids, or GTL (gas to liquid) and with specific polymers (polyisobutylenes = PIBs, olefin copolymers = ethylene/propylene copol- ymers=OCPs, polyalkyl methacrylates = PMAs) as thickeners or viscosity index improvers in addition to the customary additive components. Together with PAOs, low-viscosity esters are typically being used, for example DIDA (diisodecyl adipate), DITA (diisotridecyl adipate) or TMTC (trimethylolpropane caprylate), especially as solubilizers for polar additive types and for optimizing seal compatibilities.

Esters are used as co-solvent, especially in motor oil, turbine oil, hydraulic fluid, transmission oil, compressor oil, but esters are also used as base oils, in which they are the main compo- nent. Common esters are available by known preparation methods, and preferably from the reaction of an acid with an alcohol. WO 2014/005932 A1 discloses the use of carboxylic acid esters which are obtained by reacting aliphatic dicarboxylic acid and mixture of structurally different monoalcohols having 10 carbon atoms as lubricants and a process for their preparation. The dicarboxylic acids used are unsub- stituted dicarboxylic acids such as adipic acid.

DE 20 2013 006 323 discloses the use of di-(2-ethylhexyl)-adipate as lubricant.

WO 2014/184068 A1 describes a method for reducing the friction coefficient of a lubricating oil composition in the lubrication of a mechanical device comprising formulating the lubricating oil composition with a carboxylic acid ester derived from at one dicarboxylic acid and at least one C10 monoalcohol.

Esters based on adipic acid are well known base stocks and, thus, components for commercial- ly available lubricants for various applications. However, due to their small molecular size, adip- ic acid based diesters often show a high volatility which hampers their use in applications requir- ing high temperatures.

Thus, there is still a need for novel carboxylic acid esters which have a low viscosity and low pour points, are hydrolytically stable, have improved oxidative stability and show a low volatility.

Accordingly, it was an object of the presently claimed invention to provide carboxylic acid esters for the use as lubricants that exhibit low volatility, improved seal compatibility and improved oxi- dative stability while maintaining all other advantageous properties of branched esters such as low viscosity, low pour point, and hydrolytic and thermal stability.

Summary of the Invention

Surprisingly it was found that highly branched adipic acid esters show improved oxidative stabil- ity, seal compatibility and significantly decreased volatility while other advantageous properties of branched esters such as low viscosity, low pour point and hydrolytic and thermal stability are maintained.

The branched adipic acid esters according to the present invention satisfy all of the desired re- quirements for fully formulated lubricant basestocks by providing excellent thermal and oxidative stability, good low temperature properties (i.e. low pour points), low toxicity, low volatility, better hydrolytic stability and good seal compatibility.

Thus, in one aspect the presently claimed invention is directed to the use of at least one corn- pound of general formula (I)

wherein

Ri and R ₂ independently of each other denote linear or branched, unsubstituted Cs, Cg,

C10, C11, C12, C13, C14 alkyl

R ₃ , R _4I R ₅ and R ₆ independently of each other denote H or linear or branched, unsubstituted C ₁ ,

C ₂ , C3, C ₄ , C5, Ce, C ₇ , Ce, Cg, C10, C11, C12, C13, C14 alkyl,

with the proviso that at least one of R ₃ , R ₄ , Rs and Re is not H,

as lubricant.

In another aspect, the presently claimed invention is directed to a lubricant composition corn- prising

(A) the at least one compound of general formula (I),

wherein

R ₁ and R ₂ independently of each other denote linear or branched, unsubstituted Cs, Cg,

C-IO, C11, C12, C13, C14 alkyl

R ₃ , R ₄ , R ₅ and R ₆ independently of each other denote H or linear or branched, unsubstituted C ₁ ,

C2, C3, C ₄ , C5, Ce, C7, Cs, Cg, C10, C11, C12, C13, C14 alkyl

with the proviso that at least one of R ₃ , R ₄ , Rs and R ₆ is not H; and

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

In another aspect, the presently claimed invention is directed to a method for improving the hy- drolytic stability of lubricants comprising the step of adding to

(A) the at least one compound of general formula (I), (B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

In yet another aspect, the presently claimed invention is directed to a compound of formula (la)

Detailed Description of the Invention

Before the present compositions and formulations of the invention are described, it is to be un- derstood that this invention is not limited to particular compositions and formulations described, since such compositions and formulation may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present inven- tion will be limited only by the appended claims.

If hereinafter a group is defined to comprise at least a certain number of embodiments, this is meant to also encompass a group which preferably consists of these embodiments only. Fur- thermore, the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)" etc. and the like in the de- scription and in the claims, are used for distinguishing between similar elements and not neces- sarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illus trated herein. In case the terms "first", "second", "third" or“(A)”,“(B)” and“(C)” or "(a)", "(b)", "(c)", "(d)", "i", "ii" etc. relate to steps of a method or use or assay there is no time or time inter- val coherence between the steps, that is, the steps may be carried out simultaneously or there may be time intervals of seconds, minutes, hours, days, weeks, months or even years between such steps, unless otherwise indicated in the application as set forth herein above or below.

In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" or“in another embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suit- able manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embod- iments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

The term "lubricant" and“lubricant composition”, as used herein, shall be understood to mean a substance or mixture of substances capable of reducing friction between surfaces.

“Alkyl” denotes a moiety constituted solely of atoms of carbon and of hydrogen.

The term“branched” denotes a chain of atoms with one or more side chains attached to it. Branching occurs by the replacement of a substituent, e.g., a hydrogen atom, with a covalently bonded alkyl radical.

"Beta-position to the hydroxyl functionality’” denotes that the branching is on the carbon atom which is located beta to the hydroxyl functionality.

Compound of general formula (I)

The at least one compound of general formula (I) has the following structure

wherein

R ₁ and R ₂ independently of each other denote linear or branched, unsubstituted Cs, C ₉ ,

C10, C11, C12, C13, C14 alkyl

R ₃ , R ₄ , R ₅ and R ₆ independently of each other denote H or linear or branched, unsubstituted C ₁ ,

C2, C3, C ₄ , C5, Ce, C ₇ , Ce, Cg, C10, C11, C12, C13, C14 alkyl,

with the proviso that at least one of R ₃ , R ₄ , Rs and Re is not H.

Preferably, R1 and R2 are, independently of each other, are selected from the group consisting of /7-octyl, /7-nonyl, /7-decyl, /7-undecyl, /7-dodecyl, /7-tridecyl, /7-tetrad ecy I, isooctyl, isononyl, iso- decyl, isoundecyl, isododecyl, isotridecyl, isotetradecyl, 2-propylpentyl, 2-ethylhexyl, 2-propyl- hexyl, 2-isopropylhexyl, 2-butylhexyl, 2-/-butylhexyl, 2-propylheptyl, 2-isopropylheptyl, 2-butyl- heptyl, 2-/-butylheptyl, 2-propyloctyl, 2-isopropyloctyl, 2-butyloctyl, 2-/-butyloctyl, 2-methylnonyl, 2-ethylnonyl, 2-propylnonyl, 2-isopropylnonyl, 2-butylnonyl, 2-/-butylnonyl, 2-pentylnonanyl, 2- methyldecanyl, 2-ethyldecanyl, 2-propyldecanyl, 2-isopropyldecanyl, 2-butyldecanyl, 2-Abutyl- decanyl, 2-methylundecanyl, 2-ethylundecanyl, 2-propylundecanyl, 2-isopropylundecanyl, 2- methyldodecanyl, 2-ethyldodecanyl and 2-methyltridecanyl.

In another preferred embodiment, Ri and R ₂ are, independently of each other, selected from the group consisting of 2-propyl pentyl, 2-ethylhexyl, 2-propylhexyl, 2-isopropylhexyl, 2-butylhexyl, 2- /-butylhexyl, 2-propylheptyl, 2-isopropylheptyl, 2-butylheptyl, 2-t-butylheptyl, 2-propyloctyl, 2-iso- propyloctyl, 2-butyloctyl, 2-/-butyloctyl, 2-methylnonyl, 2-ethylnonyl, 2-propylnonyl, 2-isopropyl- nonyl, 2-butylnonyl, 2-/-butylnonyl, 2-pentylnonanyl, 2-methyldecanyl, 2-ethyldecanyl, 2-propyl- decanyl, 2-isopropyldecanyl, 2-butyldecanyl and 2-/-butyldecanyl.

In another preferred embodiment, Ri and R ₂ are, independently of one another, selected from the group consisting of 2-ethylhexyl and 2-propylheptyl.

In a particularly preferred embodiment, Ri and R ₂ are identical, selected from the group consist- ing of 2-ethylhexyl and 2-propylheptyl.

In a preferred embodiment, R ₃ , R ₄ , Rs and R ₆ are, independently of each other, selected from the group consisting of H, methyl, ethyl, /7-propyl, /7-butyl, /7-pentyl, /7-hexyl, /7-heptyl, /7-octyl, n- nonyl, /7-decyl, /7-undecyl, /7-dodecyl, /7-tridecyl, /7-tetradecyl, isopropyl, isobutyl, isopentyl, iso- hexyl, isoheptyl, isooctyl, isononyl, isodecyl, isoundecyl, isododecyl, isotridecyl , isotetradecyl and /-butyl, with the proviso that at least one of R ₃ , R ₄ , Rs and R ₆ is not H.

In another preferred embodiment, R ₃ , R ₄ , Rs and R ₆ are, independently of each other, selected from the group consisting of H, methyl, ethyl, /7-propyl and /7-butyl, with the proviso that at least one of R ₃ , R _4I R _S and R ₆ is not H.

In another preferred embodiment, R ₃ , R ₄ , Rs and R ₆ are, independently of each other, selected from the group consisting of H, methyl and ethyl, with the proviso that at least one of R ₃ , R ₄ , Rs and R ₆ is not H.

In still another embodiment, R ₃ and R ₆ are, independently of each other, selected from the group consisting of methyl and ethyl and R ₄ and Rs are H. Particularly preferably, R ₃ and R ₆ are methyl and R ₄ and Rs are H.

In a preferred embodiment, the at least one compound of general formula (I) is

wherein

R ₁ and R ₂ independently of each other denote linear or branched, unsubstituted Cs,

C10 alkyl

R3, R ₄ , R5 and R independently of each other denote H or linear or branched, unsubstituted

C1 , C2, C3, C ₄ , C5, Ce, C ₇ , Ce, Cg, C10, C11 , C12, C13, Ci ₄ alkyl,

with the proviso that at least one of R3, R ₄ , Rs and Re is not H.

In another preferred embodiment, the at least one compound of general formula (I) is

wherein

R1 and R2 independently of each other denote linear or branched, unsubstituted Cs, Cg, C ₁₀ ,

C11 , C12, C1 ₃ , Cl ₄ alkyl

R3 and Re independently of each other denote, unsubstituted Ci, C ₂ , alkyl and

R ₄ and R5 denote H.

In a particularly preferred embodiment, the at least one compound of general formula (I) is

wherein

Ri and R ₂ independently of each other denote linear or branched, unsubstituted Cs, C10 alkyl R3 and Re independently of each other denote, unsubstituted Ci , C ₂ , alkyl

R ₄ and R5 denote H.

The at least one compound of general formula (I) is obtained by reacting

(a) adipic acid which is substituted by at least one unsubstituted, linear or branched C ₁ -C ₁₄ alkyl, and

(b) at least one Cs to C14 alcohol which is branched in the beta-position to the hydroxyl

functionality.

Preferably, the adipic acid which is substituted by at least one unsubstituted C 1-C14 alkyl is se- lected from the group consisting of 2-methyl adipic acid, 2-ethyl adipic acid, 3-isopropyl adipic acid, 3-/-butyl adipic acid, 3-ethyl adipic acid, 3-methyl adipic acid, 3-propyl adipic acid, 2,5- dimethyl adipic acid, 2-methyl-5-isopropyl adipic acid, 2,5-dihexyl adipic acid, 2,5-dibutyl adipic acid, 3,4-dipropyl adipic acid, 2,3-dimethyl adipic acid, 2,4-dimethyl adipic acid, 3,4-dimethyl adipic acid, 3,3-dimethyl adipic acid, 2-ethyl-4-methyl adipic acid, 2,5-diethyl adipic acid, 2,2- diethyl adipic acid, 2,2-dimethyl adipic acid, 2,2,3-trimethyl adipic acid, 3,3,4-trimethyl adipic acid, 2,3,3-trimethyl adipic acid, 2,4,4-trimethyl adipic acid, 3,3,4,4-tetramethyl adipic acid, 2,2,4,4-tetramethyl adipic acid and 2,2,5,5-tetramethyl adipic acid.

In another preferred embodiment, the adipic acid which is substituted by at least one unsubsti- tuted C1 -C14 alkyl is selected from the group consisting of 2,3-dimethyl adipic acid, 2,4-dimethyl adipic acid, 3,4-dimethyl adipic acid, 3,3-dimethyl adipic acid, 2,2-dimethyl adipic acid, and 2,5- dimethyl adipic acid; most preferably the adipic acid which is substituted by at least one unsub- stituted C1 -C14 alkyl is 2,5-dimethyl adipic acid.

Preferably the at least one Cs to C-u alcohol which is branched in the beta-position to the hy- droxyl functionality is selected from the group consisting of /7-octanol, ^nonanol, /7-decanol, n- undecanol, /7-dodecanol, ^tridecanol, ^tetradecanol, isooctanol, isononanol, isodecanol, isoundecanol, isododecanol, isotridecanol, isotetradecanol, 2-propylpentanol, 2-ethylhexanol, 2- propylhexanol, 2-isopropylhexanol, 2-butylhexanol, 2-/-butylhexanol, 2-propylheptanol, 2- isopropylheptanol, 2-butylheptanol, 2-/-butylheptanol, 2-propyloctanol, 2-isopropyloctanol, 2-bu- tyloctanol, 2-/-butyloctanol, 2-methylnonanol, 2-ethylnonanol, 2-propylnonanol, 2-isopropyl- nonanol, 2-butylnonanol, 2-/-butylnonanol, 2-pentylnonanol, 2-methyldecanol, 2-ethyldecanol, 2- propyldecanol, 2-isopropyldecanol, 2-butyldecanol, 2-/-butyldecanol, 2-methylundecanol, 2- ethylundecanol, 2-propylundecanol, 2-isopropylundecanol, 2-methyldodecanol, 2-ethyldode- canol and 2-methyltridecanol.

In another preferred embodiment, the at least one Cs to Ci ₄ alcohol which is branched in the beta-position to the hydroxyl functionality is selected from the group consisting of 2- propylheptanol and 2-ethylhexanol.

The C ₈ to C _M alcohol which is branched in the beta-position to the hydroxyl functionality, can be present in the pure form or in the form of an isomeric mixture.

In a preferred embodiment, 2-propylheptanol is an isomeric mixture of C ₁₀ alcohols comprising 2-propylheptanol, 2-propyl-4-methylhexanol, 2-propyl-5-methylhexanol and 2-isopropylheptanol. Commercially available 2-propylheptanol such as, but not limited to, 2-propylheptanol from BASF SE may also be used for the purpose of the present invention.

Alternatively, the at least one compound of general formula (I) can also be obtained by the transesterification of

(a) adipic acid ester of formula

wherein

R3, R ₄ , R5 and R ₆ independently of each other denote H or linear or branched, unsubstitut- ed C1 , C ₂ , C3, C ₄ , C5, C6, C ₇ , Ce, Cg, C10, C11 , C12, C13, Ci ₄ alkyl

R ₇ and Rs independently of each other denote C ₁ , C ₂ alkyl

with the proviso that at least one of R3, R ₄ , Rs and R ₆ is not H; with

(b) at least one Cs to Ci ₄ alcohol which is branched in the beta-position to the hydroxyl

functionality.

Preferably, the adipic acid ester of formula (II) is selected from the group consisting of dimethyl 2-methyladipate, dimethyl 2-ethyladipate, dimethyl 3-isopropyladipate, dimethyl 3-/-butyladipate, dimethyl 3-ethyladipate, dimethyl 3-methyladipate, dimethyl 3-propyladipate, dimethyl 2,5- dimethyladipate, dimethyl 2-methyl-5-isopropyladipate, dimethyl 2,5-dihexyladipate, dimethyl 2,5-dibutyladipate, dimethyl 3,4-dipropyladipate, dimethyl 2,3-dimethyladipate, dimethyl 2,4- dimethyladipate, dimethyl 3,4-dimethyladipate, dimethyl 3,3-dimethyladipate, dimethyl 2-ethyl-4- methyladipate, dimethyl 2,5-diethyladipate, dimethyl 2,2-diethyladipate, dimethyl 2,2-dimethyl- adipate, dimethyl 2,2,3-trimethyladipate, dimethyl 3,3,4-trimethyladipate, dimethyl 2,3,3-tri- methyladipate, dimethyl 2,4,4-trimethyladipate, dimethyl 3,3,4,4-tetramethyladipate, dimethyl 2,2,4,4-tetramethyladipate, dimethyl 2,2,5,5-tetramethyladipate, diethyl 2-methyladipate, diethyl 2-ethyl adipate, diethyl 3-isopropyladipate, diethyl 3-/-butyladipate, diethyl 3-ethyladipate, dieth yl 3-methyladipate, diethyl 3-propyladipate, diethyl 2,5-dimethyladipate, diethyl 2-methyl-5-iso- propyl adipate, diethyl 2,5-dihexyladipate, diethyl 2,5-dibutyladipate, diethyl 3,4-dipropyladipate, diethyl 2,3-dimethyladipate, diethyl 2,4-dimethyladipate, diethyl 3,4-dimethyladipate, diethyl 3,3- dimethyladipate, diethyl 2-ethyl-4-methyladipate, diethyl 2,5-diethyladipate, diethyl 2,2-diethyl- adipate, diethyl 2,2-dimethyladipate, diethyl 2,2,3-trimethyladipate, diethyl 3,3,4-trimethyl- adipate, diethyl 2,3,3-trimethyladipate, diethyl 2,4,4-trimethyladipate, diethyl 3,3,4,4-tetramethyl- adipate, diethyl 2,2,4,4-tetramethyladipate and diethyl 2,2,5,5-tetramethyladipate.

In another preferred embodiment, the adipic acid of formula (II) is selected from the group con- sisting of dimethyl 2,3-dimethyladipate, dimethyl 2,4-dimethyladipate, dimethyl 3,4-dimethyl- adipate, dimethyl 3,3-dimethyladipate, dimethyl 2,2-dimethyladipate, dimethyl 2,5-dimethyl- adipate, dimethyl 2,3-dimethyladipate, diethyl 2,4-dimethyladipate, diethyl 3,4-dimethyl adipate, diethyl 3,3-dimethyladipate, diethyl 2,2-dimethyladipate and diethyl 2,5-dimethyladipate.

In a particularly preferred embodiment, the adipic acid of formula (II) is selected from the group consisting of dimethyl 2,5-dimethyladipate and diethyl 2,5-dimethyladipate.

In a preferred embodiment, the presently claimed invention is directed to the use of the at least one compound of general formula (I)

wherein

R1 and R2 independently of each other denote linear or branched, unsubstituted Cs, C ₁₀ alkyl

R ₃ , R ₄ , R ₅ and R ₆ independently of each other denote H or linear or branched, unsubstituted C ₁ ,

C ₂ , C3, C ₄ , C5, Ce, C ₇ , Ce, Cg, C10, C11, C12, C13, C14 alkyl,

with the proviso that at least one of R ₃ , R ₄ , Rs and Re is not H,

as lubricant.

In another preferred embodiment, the presently claimed invention is directed to the use of the at least one compound of general formula (I)

wherein

Ri and R ₂ independently of each other denote linear or branched, unsubstituted Cs, Cg, Cio, C

11, C12, C13, C14 alkyl

R ₃ and R ₆ independently of each other denote, unsubstituted Ci , C ₂ , alkyl

R ₄ and R ₅ denote H

as lubricant.

In a particularly preferred embodiment, the presently claimed invention is directed to the use of the at least one compound of general formula (I)

wherein

R ₁ and R ₂ independently of each other denote linear or branched, unsubstituted Ce, C ₁₀ alkyl R ₃ and R ₆ independently of each other denote, unsubstituted Ci , C ₂ , alkyl and

R ₄ and R ₅ denote H

as lubricant.

In a preferred embodiment, the presently claimed invention is directed to the use of a compound of formula (la)

as lubricant.

The compound of formula (1 a) may be interchangeably referred to as di(2-propylheptyl)-2,5- dimethyl adipate.

The compound of formula (la) is derivable from the compound of general formula (I) in which R1 and R ₂ are C10 alkyl, R ₃ and R ₆ are C1 alkyl, R ₄ and R5 are H.

Compound of formula (la) is an isomeric mixture comprising di(2-propylheptyl)-2, 5-dimethyl adipate, di(2-propyl-4-methylhexyl)-2, 5-dimethyl adipate, di(2-propyl-5-methylhexyl)-2,5- dimethyl adipate and di(2-isopropyl) heptyl-2, 5-dimethyl adipate.

In a preferred embodiment, the presently claimed invention is directed to the use of a compound of formula (lb)

as lubricant.

The compound of formula (1 b) may be interchangeably referred to as di(2-ethylhexyl)-2,5- dimethyl adipate.

The compound of formula (la) is derivable from the compound of general formula (I) in which Ri and R ₂ are Cs alkyl, R3 and Re are C1 alkyl, R ₄ and R5 are H.

In another embodiment, the presently claimed invention is directed to the use of the at least one compound of general formula (I) as lubricant in axel lubrication, medium and heavy duty engine oils, industrial engine oils, marine engine oils, automotive engine oils, crankshaft oils, compres- sor oils, refrigerator oils, hydrocarbon compressor oils, very low-temperature lubricating oils and fats, high temperature lubricating oils and fats, wire rope lubricants, textile machine oils, refrig- erator oils, aviation and aerospace lubricants, aviation turbine oils, transmission oils, gas turbine oils, spindle oils, spin oils, traction fluids, transmission oils, plastic transmission oils, passenger car transmission oils, truck transmission oils, industrial transmission oils, industrial gear oils, insulating oils, instrument oils, brake fluids, transmission liquids, shock absorber oils, heat dis- tribution medium oils, transformer oils, fats, chain oils, minimum quantity lubricants for metal- working operations, oil to the warm and cold working, oil for water-based metalworking liquids, oil for neat oil metalworking fluids, oil for semi-synthetic metalworking fluids, oil for synthetic metalworking fluids, drilling detergents for the soil exploration, hydraulic oils, in biodegradable lubricants or lubricating greases or waxes, chain saw oils, release agents, molding fluids, gun, pistol and rifle lubricants or watch lubricants and food grade approved lubricants.

The at least one compound of general formula (I) finds use as co-solvent or base stock in lubri cant composition.

The amount of the at least one compound of general formula (I) used as a co-solvent, is in the range of ³ 0.1 to £ 40 %, preferably in the range of ³ 2 to £ 40 % or > 3 to £ 40 % or > 5 to £ 40 %, or more preferably in the range of ³ 0.1 to £ 35 % or > 2 to £ 35 % or > 3 to £ 40 % or > 5 to £ 35 % or still more preferably in the range of ³ 0.1 to £ 30 % or > 2 to £ 30 % or > 3 to £ 30 % or > 5 to £ 30 % or > 0.1 to £ 25 % or > 2 to £ 25 % or > 3 to £ 25 % or > 5 to £ 25 % or > 5 to £ 20 % and most preferably in the range of ³ 0.1 to £ 15 % or > 2 to £ 15 % or > 3 to £ 15 % or > 5 to £ 15 % or > 0.1 to £ 10 % or > 2 to £ 10 % or > 3 to £ 10 % or > 5 to £ 10 % by weight, in each case, related to the total weight of the lubricant composition. The amount of the at least one compound of general formula (I) used as base stock or as a main component in a lubricant composition is in the range of ³ 40 % to £ 100 %, preferably in the range of ³ 40 % to £ 95 % or in the range of ³ 40 % to £ 90 % or more preferably in the range of ³ 40 % to £ 85 % or > 40 % to £ 80 % or > 45 % to £ 90 % or > 45 % to £ 85 % or still more preferably in the range of ³ 45 % to £ 80 % or > 45 % to £ 75 % and most preferably in the range of ³ 45 % to £ 70 % or > 50 % to £ 70 % by weight, in each case, related to the total weight of the lubricant composition.

In an aspect, the presently claimed invention is directed to a process for preparing the at least one compound of general formula (I), comprising the steps of

i) reacting (a) adipic acid which is substituted by at least one unsubstituted C-i-C-u alkyl and (b) at least one Cs to Ci ₄ alcohol which is branched in the beta-position to the hydroxyl functionality;

in the presence of at least one catalyst selected from the group consisting of titanium- containing compounds, zirconium-containing compounds and tin-containing compounds; ii) heating the mixture obtained according to step i) to a temperature in the range of ³ 80 °C to 160 °C,

iii) adding a basic aqueous solution, and iv) removing the excess Cs to Ci ₄ alcohol which is branched in the beta-position to the hy droxyl functionality.

Optionally, the carboxylic acid ester can be further purified by drying and filtering.

In a preferred embodiment, in step i) the molar ratio between the Cs to Ci ₄ alcohol which is branched in the beta-position to the hydroxyl functionality (b) and the adipic acid which is substi- tuted by at least one unsubstituted Ci-Ci ₄ alkyl (a) is in the range of ³ 2.05:1.0 to £ 3.0:1.0.

In an embodiment, the at least one catalyst is an alkyl titanate such as isopropyl butyl titanate.

Preferably, the esterification reaction between acid a) and alcohol (b) is carried out in two stag- es. In the first stage, without addition of a catalyst, the monoester of the acid (a) is formed. The temperatures to be employed in this stage depend largely on the starting materials. Satisfactory reaction rates are achieved above 100 °C, and preferably above 120 °C. It is possible to com- plete the monoester formation at these temperatures. However, it is more advantageous to in- crease the temperature continuously up to 160 °C. Water formed is removed from the reaction system as an azeotrope with the alcohol, as long as the reaction temperature is above the boil- ing point of the azeotrope (i.e. in a range from > 90 to £ 100 °C under atmospheric pressure). The course and completion of the esterification can in this case be observed via the formation of water. The use of sub atmospheric or super atmospheric pressure is not ruled out, but will be restricted to special cases. To suppress the occurrence of concentration differences, it is pre- ferred to stir the reactor contents or to mix them from time to time, e.g. by passing an inert gas through the reaction mixture.

In another embodiment of the presently claimed invention, the at least one compound of general formula (I) can be worked up by filtration optionally followed by distillation.

In the second stage, the esterification of the acid (a) is completed. The second stage is carried out in the presence of the above-described catalysts at temperatures which are above those employed in the first stage and go up to 250 °C. Water formed during the reaction is removed as an azeotrope, with the alcohol acting as an entrainer.

After completion of the reaction the reaction mixture comprises not only the desired reaction product, but also partially esterified acids, excess alcohol and the catalyst.

Preferably, the crude ester product is first neutralized with an alkaline reagent. The preferred alkaline reagent is selected from the group consisting of alkali metal hydroxide or alkaline earth metal hydroxide, preferably alkali metal hydroxide. In a particularly preferred embodiment, the alkali metal hydroxide is sodium hydroxide.

The alkaline reagent is employed as an aqueous solution containing alkali metal hydroxide in the range of ³ 0.5 % to £ 20 %, preferably in the range of ³ 0.5 % to £ 10 %, based on the overall weight of the solution. The amount of neutralizing agent to be used depends on the pro- portion of acid components, free acid and monoesters in the crude product. The use of alkaline reagent in a defined excess ensures that the acidic constituents of the reaction mixture are pre- cipitated in a crystalline, very readily filterable form. At the same time, the catalyst is largely de- composed to form likewise easily filterable products. The alkaline treatment of the crude ester is not tied to the maintenance of particular temperatures. It is advantageously carried out immedi- ately after the esterification step without prior cooling of the reaction mixture.

Subsequently any free/excess alcohol is separated from the reaction mixture. Steam distillation has been found to be useful for this step and can be carried out in simple form by passing steam into the crude product.

The removal of the free/excess alcohol is followed by the drying of the ester. In a particularly simple and effective embodiment of this step, drying is achieved by passing an inert gas through the product. The crude ester is then filtered to free it of solids. The filtration is carried out in conventional filtration equipment at room temperature or at temperatures up to 150 °C. The filtration can also be facilitated by customary filter aids such as cellulose or silica gel.

In an embodiment, the presently claimed invention is directed to the process for preparing the at least one compound of general formula (I), comprising the steps of

(i) transesterification of

(a) adipic acid ester of formula (II) which is substituted by at least one unsubstituted C-i-C-u alkyl,

wherein

R3, R ₄ , R5 and Re independently of each other denote H or linear or branched, unsubstitut- ed Ci , C2, C3, C ₄ , C5, Ce, C7, Ce, C9, C10, C11 , C12, C13, C14 alkyl

R ₇ and Rs independently of each other denote Ci , C2 alkyl,

with the proviso that at least one of R3, R ₄ , Rs and R ₆ is not H; with

(b) at least one Ce to C14 alcohol which is branched in the beta-position to the hydroxyl functionality

in the presence of at least one transesterification catalyst;

(ii) removing the excess alcohol.

Conventional processes known to the person skilled in the art can be used for the transesterifi- cation reactions.

The transesterification process according to the present invention is typically carried out in the presence of a suitable transesterification catalyst. Suitable transesterification catalysts are the conventional catalysts usually used for transesterification reactions, where these are mostly also used in esterification reactions. Among these are by way of example mineral acids, such as sulfuric acid and phosphoric acid; organic sulfonic acids, such as methanesulfonic acid and p- toluenesulfonic acid; and specific metal catalysts from the group of the tin(IV) catalysts, for ex- ample dialkyltin dicarboxylates, such as dibutyltin diacetate, trialkyltin alkoxides, monoalkyltin compounds, such as monobutyltin dioxide, tin salts, such as tin acetate, or tin oxides; from the group of the titanium catalysts: monomeric and polymeric titanates and titanium chelates, for example tetraethyl orthotitanate, tetrapropyl orthotitanate, tetrabutyl orthotitanate, triethanola- mine titanate; from the group of the zirconium catalysts: zirconates and zirconium chelates, for example tetrapropyl zirconate, tetrabutyl zirconate, triethanolamine zirconate; and also lithium catalysts, such as lithium salts, lithium alkoxides; and aluminum(lll) acetylacetonate, chromi- um(lll) acetylacetonate, iron(lll) acetylacetonate, cobalt(ll) acetylacetonate, nickel(ll) acety- lacetonate, and zinc(ll) acetylacetonate.

The amount of transesterification catalyst used is in the range of ³ 0.001 wt.% to £ 10 wt.%, preferably in the range of ³ 0.05 wt. % to £ 5 wt.%. The reaction mixture is at a temperature in the range of ³ 20°C to £ 200°C, depending on the reactants.

The transesterification can take place at ambient pressure or at reduced or elevated pressure. It is preferable that the transesterification is carried out at a pressure in the range of ³ 0.001 to £ 200 bar, particularly in the range of ³ 0.01 to £ 5 bar. The relatively low-boiling point alcohol eliminated during the transesterification is preferably continuously removed by distillation in or- der to shift the equilibrium of the transesterification reaction. The distillation column necessary for this purpose generally has direct connection to the transesterification reactor, and it is pref- erable that said column is a direct attachment thereto. If a plurality of transesterification reactors is used in series, each of said reactors can have a distillation column, or the vaporized alcohol mixture can preferably be introduced into a distillation column from the final tanks of the trans- esterification reactor cascade by way of one or more collection lines. The relatively high boiling point alcohol reclaimed in said distillation is preferably returned to the transesterification.

If an amphoteric catalyst is used, this is generally successfully removed via hydrolysis and sub- sequent removal of the metal oxide formed, for example by filtration. It is preferable that, once the reaction has taken place, the catalyst is hydrolyzed by washing with water, and that the pre- cipitated metal oxide is removed by filtration. If desired, the filtrate may be subjected to further workup for isolation and/or purification of the product. The product is preferably isolated by dis- tillation.

The transesterification can be carried out in the absence of, or in the presence of, an added organic solvent. It is preferable that the transesterification is carried out in the presence of an inert organic solvent. Among these are by way of example aliphatic hydrocarbons, halogenated aliphatic hydrocarbons, and aromatic and substituted aromatic hydrocarbons and ethers. It is preferable that the solvent is one selected from pentane, hexane, heptane, ligroin, petrol ether, cyclohexane, dichloromethane, trichloromethane, tetrachloromethane, benzene, toluene, xy- lene, chlorobenzene, dichlorobenzenes, dibutyl ether, THF, 1 ,4-dioxane, 1 ,2-dimethoxyethane and mixtures thereof. Among these are specifically toluene and THF.

The transesterification is preferably carried out at a temperature in the range of > 50 to £ 200°C. The transesterification can take place in the absence of or in the presence of an inert gas. It is preferable that the transesterification takes place without addition of any inert gas.

Subsequently any free/excess alcohol is separated from the reaction mixture. Steam distillation has been found to be useful for this step and can be carried out in simple form by passing steam into the crude product.

The removal of the free/excess alcohol is followed by the drying of the ester.

Optionally, the carboxylic acid ester can be further purified by drying and filtering.

In a preferred embodiment, the presently claimed invention is directed to the process for prepar- ing the compound of formula (la) as described herein above, comprising the steps of i) reacting (a) 2,5-dimethyl adipic acid and (b) 2-propylheptanol;

in the presence of at least one catalyst selected from the group consisting of titanium- containing compounds, zirconium-containing compounds and tin-containing compounds; ii) heating the mixture obtained according to step i) to a temperature in the range of ³ 80 °C to 160 °C,

iii) adding a basic aqueous solution, and

iv) removing the excess 2-propylheptanol.

As 2-propyheptanol is commercially available as an isomeric mixture of C10 alcohols, the reac- tion of 2,5-dimethyladipic acid with a mixture of C10 alcohols results in a mixture of esters of 2,5- dimethyladipic acid. The mixture comprises di(2-propylheptyl)-2, 5-dimethyl adipate, di(2-propyl- 4-methylhexyl)-2, 5-dimethyl adipate, di(2-propyl-5-methylhexyl)-2, 5-dimethyl adipate and di(2- isopropyl)heptyl-2, 5-dimethyl adipate.

In another preferred embodiment, the presently claimed invention is directed to the process for preparing the compound of formula (lb), comprising the steps of

i) transesterification of

(a) dimethyl 2,5-dimethyladipate, with

(b) 2-propylheptanol;

in the presence of at least one transesterification catalyst;

ii) removing the excess 2-propylheptanol.

In a preferred embodiment, the presently claimed invention is directed to the process for prepar- ing the compound of formula (lb), comprising the steps of

i) reacting (a) 2,5-dimethyl adipic acid and (b) 2-ethylhexanol;

in the presence of at least one catalyst selected from the group consisting of titanium- containing compounds, zirconium-containing compounds and tin-containing compounds; ii) heating the mixture obtained according to step i) to a temperature in the range of ³ 80 °C to 160 °C, iii) adding a basic aqueous solution, and

iv) removing the excess 2-ethylhexanol.

In another preferred embodiment, the presently claimed invention is directed to the process for preparing the compound of formula (lb), comprising the steps of

i) transesterification of

(a) dimethyl 2,5-dimethyladipate, with

(b) 2-ethylhexanol;

in the presence of at least one transesterification catalyst;

ii) removing the excess 2-ethylhexanol.

Dimethyl 2,5-dimethyladipate can be synthesized from methyl methacrylate. Dimerization of methyl methacrylate followed by hydrogenation results in Dimethyl 2,5-dimethyladipate. Such method of preparation is disclosed, for example, in the patent application EP 3110931.

In another aspect, the presently claimed invention is directed to a lubricant composition corn- prising

(A) the at least one compound of general formula (I),

wherein

R1 and R2 independently of each other denote linear or branched, unsubstituted Cs, C9,

C10, C11 , C12, C13, C14 alkyl

R3, R _4I R5 and R ₆ independently of each other denote H or linear or branched, unsubstituted C1 ,

C2, C3, C ₄ , C5, Ce, C ₇ , Ce, Cg, C10, C11 , C12, C13, C14 alkyl,

with the proviso that at least one of R3, R ₄ , Rs and Re is not H,

and

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils. In an embodiment, the presently claimed invention is directed to a lubricant composition corn- prising

(A) the compound of formula (la),

and

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

In another embodiment, the presently claimed invention is directed to a lubricant composition comprising

(A) the compound of formula (lb),

and

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

Base Oils

The lubricant compositions according to the present invention further comprise a lubricating base oil selected from the group consisting of mineral oils (Group I, II or III oils), polyalphaole- fins (Group IV oils), polymerized and interpolymerized olefins, alkyl naphthalenes, alkylene ox ide polymers, silicone oils, phosphate esters and carboxylic acid esters (Group V oils). Preferably, the lubricant base oil is selected from Group I, Group II, Group III base oils accord- ing to the definition of the API, or mixtures thereof.

Definitions for the base oils according to the present invention are the same as those found in the American Petroleum Institute (API) publication "Engine Oil Licensing and Certification Sys- tern", Industry Services Department, Fourteenth Edition, December 1996, Addendum 1 , De- cember 1998. Said publication categorizes base oils as follows: a) Group I base oils contain less than 90 percent saturates and/or greater than 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in the following table. b) Group II base oils contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in the following table. c) Group III base oils contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 120 using the test methods specified in the following table

Analytical Methods for Base oil:

d) Group IV base oils contain polyalphaolefins. Synthetic lower viscosity fluids suitable for the present invention include the polyalphaolefins (PAOs) and the synthetic oils from the hydro- cracking or hydro-isomerization of Fischer Tropsch high boiling fractions including waxes.

These are both base oils comprised of saturates with low impurity levels consistent with their synthetic origin. The hydro-isomerized Fischer Tropsch waxes are highly suitable base oils, comprising saturated components of iso-paraffinic character (resulting from the isomerization of the predominantly n-paraffins of the Fischer Tropsch waxes) which give a good blend of high viscosity index and low pour point. Processes for the hydro-isomerization of Fischer Tropsch waxes are described in U.S. Patents 5,362,378; 5,565,086; 5,246,566 and 5,135,638, as well in EP 710710, EP 321302 and EP 321304.

Polyalphaolefins suitable for the lubricant compositions according to the present invention, in- clude known PAO materials which typically comprise relatively low molecular weight hydrogen- ated polymers or oligomers of alphaolefins which include but are not limited to C ₂ to about C32 alphaolefins with the Cs to about C16 alphaolefins, such as 1-octene, 1-decene, 1-dodecene and the like being preferred. The preferred polyalphaolefins are poly-1 -octene, poly-1 -decene, and poly-1 -dodecene, although the dimers of higher olefins in the range of ³ C14 to £ C-ie provide low viscosity base stocks. Terms like PAO 4, PAO 6 or PAO 8 are commonly used specifications for different classes of polyalphaolefins characterized by their respective viscosity. For instance, PAO 6 refers to the class of polyalphaolefins which typically has viscosity in the range of 6 mm ² /s at 100 °C. A varie- ty of commercially available compositions are available for these specifications.

Low viscosity PAO fluids suitable for the lubricant compositions according to the present inven- tion, may be conveniently made by the polymerization of an alphaolefin in the presence of a polymerization catalyst such as the Friedel-Crafts catalysts including, for example, aluminum trichloride, boron trifluoride or complexes of boron trifluoride with water, alcohols such as etha- nol, propanol or butanol, carboxylic acids or esters such as ethyl acetate or ethyl propionate.

For example, the methods disclosed by U.S. Patents 3,149,178 or 3,382,291 may be conven- iently used herein. Other descriptions of PAO synthesis are found in the following U.S. Patents: 3,742,082 (Brennan); 3,769,363 (Brennan); 3,876,720 (Heilman); 4,239,930 (Allphin); 4,367,352 (Watts); 4,413,156 (Watts); 4,434,308 (Larkin); 4,910,355 (Shubkin); 4,956,122 (Watts); and 5,068,487 (Theriot). e) Group V base oils contain any base stocks not described by Groups I to IV. Examples of Group V base oils include alkyl naphthalenes, alkylene oxide polymers, silicone oils, and phos- phate esters.

Synthetic base oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as pol- ymerized and interpolymerized olefins (e.g., polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1 -hexenes), poly(l-octenes), poly(l-decenes)); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); pol- yphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and derivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic base oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxy- alkylene polymers (e.g., methyl-polyiso-propylene glycol ether having a molecular weight of 1000 or diphenyl ether of polyethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C ₃ -C ₈ fatty acid esters and C ₁₃ oxo acid diester of tetraethylene glycol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and silicate oils comprise another useful class of synthetic base oils; such base oils include tetrae- thyl silicate, tetraisopropyl silicate, tetra-(2- ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl) sili- cate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl) siloxanes and poly(methylphenyl)siloxanes. Other synthetic base oils include liquid esters of phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

Additives

In an embodiment, the lubricant composition further comprises at least one additive component (C).

The additive component (C) as used in the present invention may include an additive package and/or performance additives.

The additive package that may be used in the present invention as well as the compounds relat- ing to performance additives are considered mixtures of additives that are typically used in lub- ricant compositions in limited amounts for mechanically, physically or chemically stabilizing the lubricant compositions while special performance characteristics can be further established or improved by the individual or combined presence of such selected additives.

Besides the additive package described in the experimental part of the present application, a variety of such additive packages are known to the person skilled in the art and may commer- cially be available and typically used in lubricant compositions. One such preferred additive package that is commercially available is marketed under the name lrgalube2030A® by

BASF SE.

However, the individual components contained in the additive packages and/or the compounds further defined in the present invention as so-called performance additives include a larger number of different types of additives including dispersants, metal deactivators, detergents, extreme pressure agents (typically boron- and/or sulfur- and/or phosphorus- containing), anti- wear agents, antioxidants (such as hindered phenols, aminic antioxidants or molybdenum compounds), corrosion inhibitors, anti-foam agents, demulsifiers, pour point depressants, fric tion modifiers and mixtures thereof.

The lubricating composition of the present invention preferably comprises at least one additive component (C) selected from the group consisting of viscosity index improvers, polymeric thickeners, antioxidants, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, wear protection additives, extreme pressure additives (EP additives), anti-wear additives (AW additives), friction modifiers, metal deactivators, pour point depressants and the like.

Viscosity index improvers:

In one embodiment, the lubricant composition according to the present invention may further include at least one viscosity index improver (VII or VI improver). The viscosity index improvers include high molecular weight polymers that increase the relative viscosity of an oil at high tem- peratures more than they do at low temperatures. Viscosity index improvers include polyacry- lates, polymethacrylates, alkylmethacrylates, vinylpyrrolidone/methacrylate copolymers, poly vinylpyrrolidones, polybutenes, olefin copolymers such as an ethylene-propylene copolymer or a styrene-butadiene copolymer or polyalkene such as PIB, styrene/acrylate copolymers and polyethers, and combinations thereof. The most common VI improvers are methacrylate poly- mers and copolymers, acrylate polymers, olefin polymers and copolymers, and styrenebutadi- ene copolymers. Other examples of the viscosity index improver include polymethacrylate, polyisobutylene, alpha-olefin polymers, alpha-olefin copolymers (e.g., an ethylenepropylene copolymer), polyalkylstyrene, phenol condensates, naphthalene condensates, a styrenebutadi- ene copolymer and the like. Of these, polymethacrylate having a number average molecular weight of 10000 to 300000, and alpha-olefin polymers or alpha-olefin copolymers having a number average molecular weight of 1000 to 30000, particularly ethylene- alpha-olefin copoly- mers having a number average molecular weight of 1000 to 10000 are preferred.

The viscosity index increasing agents can be added and used individually or in the form of mix- tures, conveniently in an amount within the range of from > 0.05 to £ 20.0 % by weight, in rela- tion to the weight of the base stock.

(Polymeric) thickeners:

In one embodiment, the lubricant composition according to the present invention may further include at least one (polymeric) thickener. Suitable (polymeric) thickeners include, but are not limited to, polyisobutenes (PIB), oligomeric co-polymers (OCPs), polymethacrylates (PMAs), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

Antioxidants:

In one embodiment, the lubricant composition according to the present invention may further include at least one antioxidant. Antioxidants retard the oxidative degradation of base stocks during service. Such degradation may result in deposits on metal surfaces, such as the pres- ence of sludge, or a viscosity increase in the lubricant. One skilled in the art knows a wide vari- ety of oxidation inhibitors that are useful in lubricating oil compositions.

Antioxidants include phenolic antioxidants such as hindered phenolic antioxidants or non- phenolic oxidation inhibitors.

Useful phenolic antioxidants include hindered phenols. These phenolic antioxidants may be ashless (metal-free) phenolic compounds or neutral or basic metal salts of certain phenolic compounds. Typical phenolic antioxidant compounds are the hindered phenolics which are the ones which contain a sterically hindered hydroxyl group, and these include those derivatives of dihydroxy aryl compounds in which the hydroxyl groups are in the o or yo-position to each oth- er. Typical phenolic antioxidants include the hindered phenols substituted with alkyl groups having 6 carbon atoms or more and the alkylene coupled derivatives of these hindered phe- nols. Examples of phenolic materials of this type 2-t-butyl-4-heptyl phenol; 2-t-butyl-4-octyl phenol; 2-t-butyl-4-dodecyl phenol; 2,6-di-t-butyl-4-heptyl phenol; 2,6-di-t-butyl-4-dodecyl phe- nol; 2-methyl-6-t-butyl-4-heptyl phenol; and 2-methyl-6-t-butyl-4-dodecyl phenol. Other useful hindered mono-phenolic antioxidants may include for example hindered 2,6-di-alkyl- phenolic propionic ester derivatives. Bis-phenolic antioxidants may also be used in combination with the present invention. Examples of ortho-coupled phenols include: 2,2'-bis(4-heptyl-6-t-butyl- phenol); 2,2'-bis(4- octyl-6-t-butyl-phenol); and 2,2'-bis(4-dodecyl-6-t-butyl-phenol). Para- coupled bisphenols include for example 4,4'-bis(2,6-di-t-butyl phenol) and 4,4'- methylene- bis(2,6-di-t-butyl phenol).

Non-phenolic oxidation inhibitors which may be used include aromatic amine antioxidants and these may be used either as such or in combination with phenolics. Typical examples of non- phenolic antioxidants include: alkylated and non-alkylated aromatic amines such as aromatic monoamines of the formula R ⁸ R ⁹ R ¹⁰ N, where R ⁸ is an aliphatic, aromatic or substituted aro- matic group, R ⁹ is an aromatic or a substituted aromatic group, and R ¹⁰ is H, alkyl, aryl or R ¹¹ S(0) _x R ¹² , where R ¹¹ is an alkylene, alkenylene, or aralkylene group, R ¹² is a higher alkyl group, or an alkenyl, aryl, or alkaryl group, and x is 0, 1 or 2. The aliphatic group R ⁸ may con- tain from 1 to about 20 carbon atoms, and preferably contains from about 6 to 12 carbon at- oms. The aliphatic group is a saturated aliphatic group. Preferably, both R ⁸ and R ⁹ are aromatic or substituted aromatic groups, and the aromatic group may be a fused ring aromatic group such as naphthyl. Aromatic groups R ⁸ and R ⁹ may be joined together with other groups such as S.

Typical aromatic amines antioxidants have alkyl substituent groups of at least about 6 carbon atoms. Examples of aliphatic groups include hexyl, heptyl, octyl, nonyl, and decyl. Generally, the aliphatic groups will not contain more than about 14 carbon atoms. The general types of amine antioxidants useful in the present compositions include diphenylamines, phenyl naph- thylamines, phenothiazines, imidodibenzyls and diphenyl phenylene diamines. Mixtures of two or more aromatic amines are also useful. Polymeric amine antioxidants can also be used. Par- ticular examples of aromatic amine antioxidants useful in the present invention include: r,r'- dioctyldiphenylamine; t-octylphenyl-alpha- naphthylamine; phenyl-alphanaphthylamine; and p- octylphenyl-alpha-naphthylamine. Sulfurized alkyl phenols and alkali or alkaline earth metal salts thereof also are useful antioxidants.

Corrosion inhibitors:

In one embodiment, the lubricant composition according to the present invention may further include at least one corrosion inhibitor. Corrosion inhibitors are used to reduce the degradation of metallic parts that are in contact with the lubricant composition. Corrosion inhibitors can be described as any materials (additives, functionalized fluids, etc.) that may form a protective film on a surface that prevents corrosion agents from reacting or attacking that surface with a result- ing loss of surface material. Protective films may be absorbed on the surface or chemically bonded to the surface. Protective films may be constituted from mono-molecular species, oli- gomeric species, polymeric species, or mixtures thereof. Protective films may derive from the intact corrosion inhibitors, from their combination products, or their degradation products, or mixtures thereof. Surfaces that may benefit from the action of corrosion inhibitors may include metals and their alloys (both ferrous and non-ferrous types) and non-metals.

Corrosion inhibitors may include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and may include metal-containing compounds (salts, organometallics, etc.) and nonmetal-containing or ashless materials. Corrosion inhibitors may include, but are not limited to, additive types such as, for example, hydrocarbyl-, aryl-, alkyl-, arylalkyl-, and alkylaryl- ver- sions of detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, car- boxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphoric acid salts, amine sulfonic acid salts, alkoxylated amines, etheramines, polyethera- mines, amides, imides, azoles, diazoles, triazoles, benzotriazoles, benzothiadoles, mercapto- benzothiazoles, tolyltriazoles (TTZ-type), heterocyclic amines, heterocyclic sulfides, thiazoles, thiadiazoles, mercaptothiadiazoles, dimercaptothiadiazoles (DMTD-type), imidazoles, benzim- idazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reactions products, glycidyl ethers, anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mix- tures thereof.

Detergents:

In one embodiment, the lubricant composition according to the present invention may further comprise at least one detergent. Detergents include cleaning agents that adhere to dirt parti- cles, preventing them from attaching to critical surfaces. Detergents may also adhere to the metal surface itself to keep it clean and prevent corrosion from occurring.

Detergents include calcium alkylsalicylates, calcium alkylphenates and calcium alkaryl- sulfonates with alternate metal ions used such as magnesium, barium, or sodium. Examples of the cleaning and dispersing agents which can be used include metal-based detergents such as the neutral and basic alkaline earth metal sulphonates, alkaline earth metal phenates and alka- line earth metal salicylates alkenylsuccinimide and alkenylsuccinimide esters and their borohy- drides, phenates, salienius complex detergents and ashless dispersing agents which have been modified with sulphur compounds. These agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from > 0.01 to £ 1.0 % by weight in relation to the weight of the base stock; these can also be high total base number (TBN), low TBN, or mixtures of high/low TBN. Dispersants:

In one embodiment, the lubricant compositions according to the present invention further corn- prises at least one dispersant. Dispersants are lubricant additives that help to prevent sludge, varnish and other deposits from forming on critical surfaces. The dispersant may be a succin- imide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dis persant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl mono- carboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hy- drocarbyl-amine dispersant, a polyether dispersant or a polyetheramine dispersant.

In one embodiment, the succinimide dispersant includes a polyisobutylene-substituted succin- imide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000, or of about 950 to about 1600. Succin- imide dispersants and their methods of preparation are more fully described in U.S. Patents 4,234,435 and 3,172,892. Suitable ester-containing dispersants are typically high molecular weight esters. These materials are described in more detail in U.S. Patent 3,381 ,022.

In one embodiment, the dispersant includes a borated dispersant. Typically, the borated dis persant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

Anti-foam agents:

In one embodiment, the lubricant compositions according to the present invention further corn- prises at least one anti-foam agent. Anti-foam agents may be selected from silicones, poly- acrylates, and the like. The amount of anti-foam agent in the lubricant compositions described herein may range from > 0.001 wt.-% to£ 0.1 wt.-% based on the total weight of the formula- tion. As a further example, an anti-foam agent may be present in an amount from about 0.004 wt.-% to about 0.008 wt.-%.

Extreme pressure additives (EP additives):

In one embodiment, the lubricant compositions according to the present invention further corn- prises at least one extreme pressure additive. In one embodiment, according to the present invention, the extreme pressure agent is a sulfur-containing compound. In one embodiment, the sulfur-containing compound may be a sulfurised olefin, a polysulfide, or mixtures thereof. Ex- amples of the sulfurised olefin include a sulfurised olefin derived from propylene, isobutylene, pentene; an organic sulfide and/or polysulfide including benzyldisulfide; bis-(chlorobenzyl) di- sulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurised methyl ester of oleic acid, a sulfurised alkylphenol, a sulfurised dipentene, a sulfurised terpene, a sulfurised Diels-Alder adduct, an alkyl sulphenyl N'N- dialkyl dithiocarbamates; or mixtures thereof. In one embodiment, the sulfurised olefin includes a sulfurised olefin derived from propylene, isobutylene, pentene or mixtures thereof.

In one embodiment, according to the present invention, the extreme pressure additive sulfur- containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Ex- amples of the dimercaptothiadiazole include compounds such as 2,5-dimercapto-1 ,3,4- thiadiazole or a hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2, 5-dimercapto-1 ,3,4-thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-1 ,3,4-thiadiazole derived compounds include for example 2,5-bis(tert-nonyldithio)-1 ,3,4-thiadiazole or 2-tert- nonyldithio-5-mercapto-1 ,3,4-thiadiazole. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16.

Extreme pressure additives include compounds containing boron and/or sulfur and/or phospho- rus. The extreme pressure agent may be present in the lubricant compositions at 0 wt.-% to about 20 wt.-%, or at about 0.05 wt.-% to about 10.0 wt.-%, or at about 0.1 wt.-% to about 8 wt.-% of the lubricant composition.

Anti-wear additives (AW additives):

In one embodiment, the lubricant compositions according to the present invention further corn- prises at least one anti-wear additive. Examples of anti-wear additives include organo borates, organo phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyl dithiophosphates, zinc diaryl dithiophos- phates, phosphosulfurized hydrocarbons and any combinations thereof.

Friction modifiers:

In another embodiment, the lubricant compositions according to the present invention includes at least one friction modifier. A friction modifier is any material or materials that can alter the coefficient of friction of a surface lubricated by any lubricant or fluid containing such material(s). Friction modifiers, also known as friction reducers, or lubricity agents or oiliness agents, and other such agents that change the ability of base oils, formulated lubricant compositions, or functional fluids, to modify the coefficient of friction of a lubricated surface may be effectively used in combination with the base oils or lubricant compositions of the present invention if de- sired. Friction modifiers may include metal-containing compounds or materials as well as ash- less compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal-ligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Such metal-containing friction modifiers may also have low-ash char- acteristics. Transition metals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands may include hydrocarbyl derivative of alcohols, polyols, glycerols, partial ester glycerols, thiols, car- boxylates, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithio- phosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing effective amounts of O, N, S, or P, indi vidually or in combination. In particular, Mo-containing compounds can be particularly effective such as for example Mo-dithiocarbamates, Mo(DTC), Mo-dithiophosphates, Mo(DTP), Mo- amines, Mo (Am), Mo-alcoholates, Mo- alcohol-amides, and the like.

Ashless friction modifiers may also include lubricant materials that contain effective amounts of polar groups, for example, hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycer- ides, glyceride derivatives, and the like. Polar groups in friction modifiers may include hydro- carbyl groups containing effective amounts of O, N, S, or P, individually or in combination. Oth- er friction modifiers that may be particularly effective include, for example, salts (both ash- containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hy- droxyl-containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alco- hols, amides, esters, hydroxy carboxylates, and the like. In some instances, fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers.

Examples of friction modifiers include fatty acid esters and amides, organo molybdenum corn- pounds, molybdenum dialkylthiocarbamates and molybdenum dialkyl dithiophosphates.

Metal deactivators:

In another embodiment, the lubricant compositions according to the present invention further comprises at least one metal deactivator. In various embodiments, one or more metal deactiva- tors can be included in the composition. Suitable, non-limiting examples of the one or more metal deactivators include benzotriazoles and derivatives thereof, for example 4- or 5- alkylbenzotriazoles (e.g. triazole) and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole and 5,5'-methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, e.g. 1 -[bis(2- ethylhexyl) aminomethyl) triazole and 1-[bis(2- ethylhexyl) aminomethyl)benzotriazole; and alkoxyalkylbenzotriazoles such as 1 -(nonyloxymethyl)benzotriazole, 1-(1- butoxyethyl)benzotriazole and 1-(1-cyclohexyloxybutyl) triazole, and combinations thereof.

Additional non-limiting examples of the one or more metal deactivators include 1 ,2,4-triazoles and derivatives thereof, for example 3-alkyl(or aryl)-1 , 2,4-triazoles, and Mannich bases of 1 ,2,4-triazoles, such as 1-[bis(2-ethylhexyl) aminomethyl -1 , 2,4-triazole; alkoxyalky1 -1 , 2,4- triazoles such as 1-(1-butoxyethyl)-1 , 2,4-triazole; and acylated 3-amino-1 , 2,4-triazoles, imid- azole derivatives, for example 4,4'-methylenebis(2-undecyl-5-methylimidazole) and bis[(N- methyl)imidazol-2-yl]carbinol octyl ether, and combinations thereof.

Further non-limiting examples of the one or more metal deactivators include sulfur-containing heterocyclic compounds, for example 2-mercaptobenzothiazole, 2,5-dimercapto-1 , 3,4-thia- diazole and derivatives thereof; and 3,5-bis[di(2- ethylhexyl) aminomethyl]-1 , 3,4-thiadiazolin-2- one, and combinations thereof. Even further non-limiting examples of the one or more metal deactivators include amino compounds, for example salicylidenepropylenediamine, salicylami- noguanidine and salts thereof, and combinations thereof.

The one or more metal deactivators are not particularly limited in amount in the composition but are typically present in an amount of from about 0.01 to about 0.1 , from about 0.05 to about 0.01 , or from about 0.07 to about 0.1 , wt.-% based on the weight of the composition. Alterna- tively, the one or more metal deactivators may be present in amounts of less than about 0.1 , of less than about 0.7, or less than about 0.5, wt.-% based on the weight of the composition.

Pour point depressants:

In another embodiment, the lubricant compositions according to the present invention further comprises at least one pour point depressant. Pour point depressants (PPD) include polymeth- acrylates, alkylated naphthalene derivatives, and combinations thereof. Commonly used addi- tives such as alkylaromatic polymers and polymethacrylates are also useful for this purpose. Typically, the treat rates range from > 0.001 wt.-% to £ 1.0 wt.-%, in relation to the weight of the base stock.

Demulsifiers:

In another embodiment, the lubricant compositions according to the present invention further comprises at least one demulsifier. Demulsifiers include trialkyl phosphates, and various poly- mers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof. Another advantageous property of the carboxylic esters to be used in accordance with the in- vention is their high hydrolytic stability. The hydrolytic stability is determined by measuring the acid value during a 9-day reaction with water at 100 °C as described in“Svensk Standard SS- 155181”.

In an aspect, the presently claimed invention is directed to a method for improving the hydrolytic stability of lubricants comprising the step of adding to

(A) the at least one compound of general formula (I),

wherein

R1 and R2 independently of each other denote linear or branched, unsubstituted Cs, C9,

C10, C11 , C12, C13, C14 alkyl

R3, R ₄ , R5 and Re independently of each other denote H or linear or branched, unsubstituted C1 ,

C2, C3, C ₄ , C5, Ce, C7, Ce, C9, C10, C11 , C12, C13, Ci ₄ alkyl with the proviso that at least one of R3, R ₄ , Rs and R ₆ is not H,

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

In an embodiment, the presently claimed invention is directed to a method for improving the hydrolytic stability of lubricants comprising the step of adding to

(A) the compound of formula (la),

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils.

In an embodiment, the presently claimed invention is directed to a method for improving the hydrolytic stability of lubricants comprising the step of adding to

(A) the compound of formula (lb),

(B) at least one base oil selected from Group I mineral oils, Group II mineral oils, Group III mineral oils, Group IV oils and Group V oils. In another aspect, the presently claimed invention is directed to a compound of formula (la)

Examples

Di (2-Propylheptyl) adipate is available from BASF SE, Ludwigshafen

2-Propyl-heptanol [93.0 % by weight 2-propyl-heptanol; 2.9 % by weight 2-propyl-4-methyl- hexanol; 3.9 % by weight 2-propyl-5-methylhexanol and 0.2 % by weight 2-isopropylheptanol] is commercially available from BASF SE, Ludwigshafen

2,5-Dimethyl adipic acid is synthesized from methyl methacrylate by the procedure as reported in patent application EP 31 10931 (Example no. 11.1 and II.2).

Methods

Hydrolysis test

The hydrolytic stability was determined by measuring the acid value during a 9-day reaction with water at 100 °C as described in“Svensk Standard S-155181”.

Preparation of Di (2-propylheptyl)-2,5-dimethyladipate (Formula la)

Example 1

Preparation of Di (2-propylheptyl)-2,5-dimethyladipate by esterification of 2,5-dimethyl adipic acid

2-Propylheptanol (2.4 mol) and 2,5-dimethyl adipic acid (1.0 mol) were reacted in the present of isopropyl butyl titanate (0.001 mol) in an autoclave under inert gas (N ₂ ) at a reaction tempera- ture of 230°C. Water formed during the reaction was removed from the reaction mixture through an inert gas stream (I h-stream). After 180 minutes, excess 2-propylheptanol was removed from the mixture by distillation at a pressure of 50 mbar. The obtained Di (2-propylheptyl)-2,5- dimethyladipate was neutralised with 0.5% NaOH at 80 °C. The organic phase was separated from the aqueous phase, followed by washing with water. The crude 2,5-dimethyl adipic acid ester was purified by passing it over steam at 180°C and 50 mbar followed by drying under N ₂ stream at 150°C and 50 mbar. The ester was mixed with activated carbon and filtered using a rheological agent supra-theorit at 80°C under reduced pressure.

Example 2 Preparation of Di (2-propylheptyl)-2,5-dimethyladipate by transesterification of dimethyl 2,5- dimethyladipate

Dimethyl 2,5-dimethyladipate (0.03 mol, 6 g), 2-propylheptanol (0.15 mol, 23.5 g) and concen- trated H ₂ SO ₄ (0.003 mol, 0.3 g) were heated at 140°C for 2 hours at 1013 mbar. Methanol formed during the reaction was removed at 450 mbar. NaHCC>3 (0.007 mol, 0.6 g) was added to the reaction mixture, followed by the removal of the excess of 2-propylheptanol by distillation at 1 mbar and 110°C. Di (2-propylheptyl)-2,5-dimethyladipate was obtained as a clear colourless liquid at 0.1 mbar and 210°C (0.02 mol, 9.1 g, yield: 66.7 %, purity 99.6%). The identity and purity of the final product was determined by means of gas chromatography and ¹ H- and ¹³ C- NMR.

Table 1

The above outlined table indicates that the inventive carboxylic acid ester of formula (la) has better oxidative stability as indicated by the DSC value, improved seal compatibility as indicated by a decrease in percentage of the volume change and improved volatility as indicated by a decrease in Noack volatility, compared to Di (2-propylheptyl) adipate while maintaining the vis- cosity, pour point and hydrolytic stability.