TECHNICAL FIELD

The present invention relates to a methodology to reductively cleave the β-Ο-4 ether bond in a monomeric or polymeric compound.

BACKGROUND

Reductive cleavage of the β-Ο-4 bond in lignin is a rare transformation. One example using a simplified lignin model compound was performed by the Bergman group (Nichols, J.M.; Bishop, L.M.; Bergman, R.G.; Ellman, J.A. "Catalytic C-0 Bond Cleavage of 2-Aryloxy- l-arylethanols and its Application to the

Depolymerization of Lignin Related Polymers" J. Am. Chem. Soc. 2010, 132, 12554- 12555). In this publication, a Ru-based catalyst performed the cleavage to generate the acetophenone and the phenol. A disadvantage is that inert atmosphere was required for efficient catalysis.

Very recently, a Ni catalyzed reduction of different model compounds and also pyrolysis oil was reported using isopropanol as hydrogen donor (X. Wang, R.

Rinaldi, "Exploiting H-transfer reactions with RANEY Ni for upgrade of phenolic and aromatic biorefinery feeds under unusual, low-severity conditions", Energy Environ. Sci., 2012, 5, 8244). The main transformation described in said publication is the reduction of the aromaticity in aromatic compounds to generate the saturated hydrocarbons. The authors also show with a few examples that phenolic and benzylic ethers are cleaved to generate saturated alcohols or hydrocarbons.

However, the authors do not include the β-Ο-4 bond in a simplified or parent model. This bond is much more difficult to cleave than to cleave the highly activated phenolic and benzylic bonds, which are considered standard procedures. Another disadvantage with the previous report using Ni was that an excess of the metal was used. Thereby, the metal was not used in catalytic amount, and may only be considered to mediate and not catalyze the reaction.

It is well known that Ni is active in the hydrogenolysis of aryl ethers using hydrogen gas (A. G. Sergeev, J. F. Hartwig, "Selective, Nickel-catalyzed Hydrogenolysis of Aryl Ethers" Science, 2011, 332, 439-443). Also, that Ni and hydrogen gas or hydrogen donor is active in the reduction of the aromaticity in phenols and other aromatic compounds (C. Zhao, Y. Kou, A. A. Lemonidou, X. Li, J. A. Lercher,

"Hydrodeoxygenation of bio-derived phenols to hydrocarbons using RANEY® Ni and Nafion/Si0 ₂ catalysts," Chem. Commun., 2010, 46, 412-414).

SUMMARY OF THE INVENTION

As described above, Ni with hydrogen or a hydrogen donor is known to reduce the aromaticity and also to cleave benzyl and phenyl ether bonds. However, the combination of Ni and a mild hydrogen donor is not known to cleave the β-Ο-4 bond in simplified or parent lignin model, lignin, lignosulfonate, or lignin from other pulping or separation method.

The object of the present invention is to provide a way to perform a cleavage of the β-Ο-4 bond in lignin using an alcohol as the hydrogen donor by means of catalysis. This has to the knowledge of the present inventors never before been presented.

The invention can be used in the depolymerization of lignin to generate hydrocarbon monomers that can be used as fine chemical feed-stock or fuel additives.

One aspect of the present invention relates to a method of reducing a β-Ο-4 bond bond to the corresponding C-H bond in a compound using a hydrogen donor and a metal catalyst.

Another aspect of the present invention relates to a method in which the metal catalyst is not used in stoichiometric or over stoichiometric amount.

Preferred embodiments of the above mentioned aspect are described below; all the embodiments below should be understood to refer to both aspects described above.

In one embodiment the hydrogen donor is glycerol, glucol, glucose, isopropanol, methanol or ethanol.

In another embodiment one solvent is a polar, unpolar, protic or aprotic solvent.

In another embodiment one solvent is selected between isopropanol, methanol, ethanol, water, ethylacetate, or a combination of two or more of the listed solvents. In another embodiment the hydrogen donor is formic acid or hydrogen gas.

In another embodiment the hydrogen donor is not hydrogen gas.

In another embodiment the reaction is conducted at a temperature of at least 40°C, preferably 70- 120 °C.

In another embodiment the catalyst is nickel on carbon or Raney nickel.

In another embodiment the compound is a β-Ο-4 bond in a lignin model compound.

In another embodiment the compound is a polymer.

In another embodiment the compound is a biopolymer.

In another embodiment the compound is lignin.

In another embodiment the compound is lignosulfonate.

In another embodiment the reaction is conducted in an atmosphere of carbon dioxide.

In another embodiment the catalyst is used in 0.1-300 mol%. DESCRIPTION OF FIGURES

Figure 1. Simplified lignin model containing a β-Ο-4 bond.

Figure 2. Parent lignin model compound containing a β-Ο-4 bond.

Figure 3. A) HPLC chromatogram of black liquor before the reaction. B) HPLC chromatogram of black liquor after the reaction.

DETAILED DESCRIPTION

In the present invention the term "hydrogen donor" should be interpreted as a substance or compound that gives or transfers hydrogen atoms to another substance or compound. The invention relates to a method to reductively cleave a substrate, wherein said substrate involves the β-Ο-4 bond, which is abundant in lignin.

A general method comprises adding a catalyst to a reaction flask or container, adding a solvent followed by addition of a hydrogen donor and the substrate to be reduced. The reaction is then stopped or quenched and the obtained product is isolated and preferably dried.

The phenyl group may be substituted in ortho, meta or para position. The reaction is performed using a transition metal catalyst (Ni) to generate the hydrocarbon in good (45-65% yield) to excellent yields (65-100% yield) with only water as side product. A suitable catalytic amount of catalyst can be 0.1 to 300 mol%, such as 0.5 mol% or more, or 1 mol% or more, or 2 mol% or more, or 4 mol% or more, or 5 mol% or more, or 8 mol% or more, or 250 mol% or less, or 200 mol% or less, or 150 mol% or less, or 100 mol% or less, or 50 mol% or less, or 20 mol% or less, or 15 mol% or less or 12 mol% or less or 10 mol% or less.

The reactions can be performed under mild reaction conditions (40 °C - 120 °C) by conventional heating or by heating in a microwave oven, but can also be performed at higher reaction temperatures.

When using a carbon dioxide atmosphere, the atmosphere may comprise other compounds such as oxygen and nitrogen. The atmosphere could be air comprising carbon dioxide or an inert atmosphere (such as argon or nitrogen gas) comprising carbon dioxide.

The following compounds are non-limiting examples of substrates that could be reduced by the method according to the invention: phenylmethanesulfonic acid, 3- (4-(2-(4-hydroxy-3-methoxyphenyl)-2-oxoethoxy)phenyl)acrylal dehyde, ethyl 3-(4-(2- (4-hydroxy-3-methoxyphenyl)-2-oxoethoxy)phenyl)acrylate, 2-phenoxy- 1 - phenylethanone and l,4-bis(benzo[d][l,3]dioxol-5-yl)hexahydrofuro[3,4-c]furan, 1- (3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane- l,3-diol, lignin, black liquor from Kraft pulping, lignosulfonate. EXAMPLES

Example 1 : 1 - (3,4-dimethoxyphenyl) -2 - (2 -methoxyphenoxy)propane- 1 ,3-diol.

Raney Ni 4200 ( 17 mg, 3.4 x 10 ⁴ mol, 20 mol%) is weighed into a reaction flask. Ethyl acetate (4 mL), isopropanol (20 μΐ _^ , 2 x 10 ⁴ mol) and l-(3,4-dimethoxyphenyl)- 2-(2-methoxyphenoxy)propane- l,3-diol (1.6 ^x 10 ⁴ mol, 54 mg), is added and the reaction flask is capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The phenol is extracted with Na ₂ C03, the solvents are evaporated and the product is purified by column chromatography. The products was analyzed by Ή and ¹³ C NMR

spectroscopy and corresponded to a 1 : 1 : 1 mixture of l-phenylpropane- l,3-diol, propiophenone, and l-cyclohexylpropane- l,3-diol in above 95% yield.

Example 2: 2-phenoxy- l-phenylethanol

Raney Ni 4200 ( 17 mg, 3.4 x 10 ⁴ mol, 20 mol%) is weighed into a reaction flask. Ethyl acetate (4 mL), isopropanol (20 μL, 2 x 10 ⁴ mol) and and 2-phenoxy-l- phenylethanol ( 1.6 x 10" ⁴ mol, 34 mg), is added and the reaction flask is capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The phenol is extracted with Na ₂ C03, the solvents are evaporated and the other product is purified by column

chromatography. The product acetophenone was analyzed by Ή NMR and produced in 100% yield.

Example 3: 2-phenoxy- l-phenylethanol

Raney Ni 4200 ( 17 mg, 3.4 x 10 ⁴ mol, 20 mol%) is weighed into a reaction flask. Isopropanol (4 mL) and 2-phenoxy- l-phenylethanol ( 1.6 x 10 ⁴ mol, 34 mg), is added and the flask capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The solvents are evaporated and the product is purified by column chromatography. The product cyclohexanol and cyclohexyl- l-ethanol was analyzed by Ή NMR and produced in 60% yield. Example 4: 2-phenoxy- l-phenylethanol

Raney Ni 4200 (100 mg, 20 x 10 ⁴ mol, 100 mol%) is weighed into a reaction flask. Isopropanol (4 mL) and 2-phenoxy- l-phenylethanol (1.6 x 10 ⁴ mol, 34 mg), is added and the flask capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The solvents are evaporated and the product is purified by column chromatography. The product cyclohexanol and cyclohexyl- l-ethanol was analyzed by Ή NMR and produced in 90% yield.

Example 5: 2-phenoxy- l-phenylethanol

Raney Ni 4200 (100 mg, 20 x 10 ⁴ mol, 100 mol%) is weighed into a reaction flask. Ethyl acetate (4 mL) and 2-phenoxy- l-phenylethanol (1.6 x 10 ⁴ mol, 34 mg), is added and the flask capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The solvents are evaporated and the product is purified by column chromatography. The product acetophenone and phenol was analyzed by Ή NMR and produced in 40% yield.

Example 6: Reaction of black liquor from Kraft process.

Raney Ni 4200 (17 mg, 3.4 x 10 ⁴ mol, 20 mol%) is weighed into a reaction flask. Isopropanol (4 mL) and black liquor from the Kraft process (50 mg, dry), is added and the reaction flask is capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The reaction mixture is injected into an HPLC-system and run on a silica column in Isopropanol-Hexane. Figure 3, show the results from the reaction mixture and the starting material.

Example 7: Reaction of red liquor (lignosulfonate) from sulfite process.

Raney Ni (17 mol%, 3.4 x 10 ⁴ mol, 20 mol%)) is weighed into a reaction flask.

Isopropanol (3 mL) and lignosulfonate (50 mg, dry), is added and the reaction flask is capped with a rubber septa and the mixture is heated (100 °C). The reaction is run for 24 hours and the reaction mixture is filtered. The reaction mixture is injected into an HPLC-system and run on a silica column in Isopropanol-Hexane. Example 8: 2-phenoxy- l-phenylethanol

Nickel on carbon (50 mg, 20 x 10 ⁴ mol, 10 mol%) is weighed into a reaction flask. Isopropanol (4 mL) and 2-phenoxy- l-phenylethanol (1.6 x 10 ⁴ mol, 34 mg), is added and the flask capped with a rubber septa and the mixture is heated (80 °C). The reaction is run for 4 hours and the reaction mixture is filtered. The solvents are evaporated and the product is purified by column chromatography. The product acetophenone and phenol was analyzed by Ή NMR and produced in 80% yield.