Processes for the Production of Vanillin and Related Compounds

Abstract

The present invention generally relates to the production of vanillin and related compounds (such as aromatic carboxylic acids, quinones, etc.) involving the oxidative cleavage of aromatic compounds (such as lignin, lignols, cinnamic acid and its derivatives, etc.) under mild reaction conditions. More specifically, the present invention provides processes for the production of vanillin involving the oxidative cleavage of an aromatic compound, such as lignin or ferulic acid, using a peroxide based oxidant, such as hydrogen peroxide, in the presence of a suitable catalysis, such as vanadium oxide.

Claims

1. A process for the production of vanillin or a related compound comprising the step of reacting an aromatic compound with a peroxide in the presence of a suitable catalyst, wherein said catalyst is a vanadium compound.

2. The process according to claim 1, wherein the aromatic compound is selected from the group consisting of lignin and monomeric analogues thereof, lignols (such as coumaryl alcohol, coniferyl alcohol or sinapyl alcohol), cinnamic acid and derivatives thereof (such as ferulic acid).

3. The process according to claim 1, wherein the aromatic compound is lignin or a monomeric analogue thereof.

4. The process according to claim 1, wherein the aromatic compound is cinnamic acid or a derivative thereof or wherein the aromatic compound is ferulic acid.

5. The process according to claim 1, wherein the aromatic compound is a cinnamic acid derivative according to general formula (I) ##STR00006## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently selected from the group consisting is selected from the group consisting of hydrogen, hydroxyl, halogen, NO.sub.2, C.sub.1-6 alkyl optionally substituted with one or more halogens, and C.sub.1-6 alkoxy optionally substituted with one or more halogens, with the proviso that at least one of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is not hydrogen.

6. (canceled)

7. The process according to claim 1, wherein the peroxide is selected from the group consisting of hydrogen peroxide, organic hydroperoxides, percarboxylic acids, organic peroxides and diacyloyl peroxides.

8. The process according to claim 1, wherein the peroxide is employed in an amount of 5 to 40 equivalents per aromatic ring of the aromatic compound.

9. The process according to claim 1, wherein the aromatic compound is lignin and the peroxide is employed in an amount of from 5 to 200 wt % per mass of lignin.

10. The process according to claim 1, wherein the peroxide is hydrogen peroxide.

11. The process according to claim 10, wherein the hydrogen peroxide is employed as an aqueous solution in the range of 10% to 60%.

12. The process according to claim 1, wherein the catalyst is a vanadium oxide.

13. The process according to claim 12, wherein the vanadium oxide is selected from the group consisting of Vanadium (II) oxide (vanadium monoxide, VO), Vanadium (III) oxide (vanadium trioxide, V.sub.2O.sub.3), Vanadium (IV) oxide (vanadium dioxide, VO.sub.2) and Vanadium (V) oxide (vanadium pentoxide, V.sub.2O.sub.5), (VO(acac) 2, VCl.sub.2, VOSO.sub.4, VOCl.sub.3, vanadates including VO.sub.3.sup. and VO.sub.4.sup.3 (such as Na.sub.3VO.sub.4 and NH.sub.4VO.sub.3).

14. (canceled)

15. The process according to claim 1, wherein the catalyst is employed in an amount of from 0.01 to 1 equivalent per aromatic ring of aromatic compound.

16. The process according to claim 12, wherein the vanadium oxide is employed in amount of 0.02 to 0.1, such as 0.05, equivalents per aromatic ring of the aromatic compound.

17. The process according to claim 1, wherein the aromatic compound is lignin and the catalyst is employed in an amount of from 1 to 100 wt % per mass of lignin.

18. The process according to claim 14, wherein the aromatic compound is lignin and the vanadium oxide is employed in amount of 2 to 10 wt %.

19. (canceled)

20. The process according to claim 1, wherein the reaction is carried out in a solvent and the solvent is selected from the group consisting of dimethoxyethane (DME), acetonitrile (MeCN), ethanol (EtOH), tetrahydrofuran (THF), methanol (MeOH), dichloromethane (DCM), heptane, ethyl acetate (EtOAc), diethyl ether, isopropanol, dimethyl carbonate (DMC) and 2,2,2-trifluoroethanol (TFE).

21. (canceled)

22. The process according to claim 1, wherein the reaction is carried out at a temperature in the range of 0 C. to reflux temperature.

23. (canceled)

24. (canceled)

25. The process according to claim 1, wherein the reaction is carried out for at least 10 min.

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. The process according to claim 1, further comprising recovering vanillin and/or said related compound.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0045] FIG. 1: Schematic representation of lignin and lignols

[0046] FIG. 2: Conversion of ferulic acid to vanillin, vanillic acid and the corresponding quinone

[0047] FIG. 3: Conversion of various derivatives of cinnamic acid to corresponding derivatives of benzaldehydes and benzoic acids

[0048] FIG. 4: Conversion of various derivatives of hydroxycinnamic acid to corresponding derivatives of benzaldehydes, benzoic acids and benzoquinones.

[0049] FIG. 5: Reaction profile for vanillin formation.

[0050] FIG. 6: The effect of the amount of hydrogen peroxide on the oxidative cleavage of CC double bond.

[0051] FIG. 7: Reaction profile for benzoic acid formation.

[0052] The present invention is now described in more detail below.

DETAILED DESCRIPTION OF THE INVENTION

[0053] As noted above, the present invention is based on the surprising finding that vanillin and related compounds, such as aromatic carboxylic acids, quinones, etc., can be produced from aromatic compounds, such as lignin, lignols, or cinnamic acid and its derivatives (e.g., ferulic acid), in a green and environmentally friendly manner using a peroxide as oxidant, such as hydrogen peroxide, in the presence of a suitable catalysis, such as vanadium (V) oxide. The advantage of the processes of the present invention is a) selectivity, as only vanillin and no other aromatic aldehydes derived from lignin are formed; b) the use of a green oxidant, such as hydrogen peroxide, which produces only water as a by-product, c) a simple and inexpensive catalyst, and d) versatility of production of other products (vanillic acid, benzoic acid, benzaldehyde, quinone, etc.).

[0054] The present invention thus provides a process for the production of vanillin or a related compound comprising the step of reacting an aromatic compound with a peroxide in the presence of a suitable catalyst.

[0055] According to some embodiments, the process is for the production of vanillin.

[0056] According to some embodiments, the process is for the production of a vanillin related compound, such as vanillic acid, benzoic acid, benzaldehyde or a quinone, such as a benzoquinone. According to some embodiments, the process is for the production of vanillic acid. According to some embodiments, the process is for the production of benzoic acid. According to some embodiments, the process is for the production of benzaldehyde. According to some embodiments, the process is for the production of a quinone, such as a benzoquinone. According to some embodiments, the process is for the production of a benzoquinone, such as 2-methoxy-1,4-benzoquinone.

[0057] The aromatic compound may be any aromatic compound which comprises at least one saturated six-membered carbocyclic ring and can be converted into vanillin or a related compound. Non-limiting examples of such aromatic compounds are lignin or monomeric analogues thereof, lignols and cinnamic acids.

[0058] According to some embodiments, the aromatic compound is lignin or a monomeric analogue thereof, such as a lignol. According to some embodiments, the aromatic compound is lignin.

[0059] According to some embodiments, the aromatic compound is a lignol, such as coumaryl alcohol, coniferyl alcohol or sinapyl alcohol.

[0060] According to some embodiments, the aromatic compound is cinnamic acid or a cinnamic acid derivative. According to some embodiments, the aromatic compound is cinnamic acid. According to some embodiments, the aromatic compound is a cinnamic acid derivative.

[0061] According to some embodiments, the aromatic compound is a cinnamic acid derivative according to general formula (I)

##STR00002## [0062] wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are each independently selected from the group consisting is selected from the group consisting of hydrogen, hydroxyl, halogen, NO.sub.2, C.sub.1-6 alkyl optionally substituted with one or more halogens, and C.sub.1-6 alkoxy optionally substituted with one or more halogens, with the proviso that at least one of R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 is not hydrogen.

[0063] According to some embodiments, the cinnamic acid derivative is selected from the group consisting of ferulic acid, p-coumaric acid, sinapinic acid, 3-chlorocinnamic acid, 4-chlorocinnamic acid, 4-fluorocinnamic acid, 4-methylcinnamic acid, 4-bromocinnamic acid, 4-nitrocinnamic acid and 4-methylcinnamic acid.

[0064] According to some embodiments, the aromatic compound is a hydroxycinnamic acid according to general formula (II)

##STR00003## [0065] wherein X, Y and Z are each independently selected from the group consisting of hydrogen, hydroxyl, halogen, NO.sub.2, C.sub.1-6 alkyl optionally substituted with one or more halogens, and C.sub.1-6 alkoxy optionally substituted with one or more halogens, with the proviso that at least one of X, Y and Z is hydroxyl.

[0066] According to some embodiments, the aromatic compound is ferulic acid, p-coumaric acid or sinapinic acid.

[0067] According to some embodiments, the aromatic compound is ferulic acid.

[0068] The aromatic compound, such as lignin or ferulic acid, may be provided as pure chemical or may be provided in the form of a composition comprising any one thereof, including a mixture thereof. For example, lignin and/or ferulic acid may be provided in the form of a lignocellulosic biomass or extract thereof. Lignin may also be provided in the form of black liquor, which is an aqueous solution comprising lignin residues obtained as waste after paper production. The lignin may also be in the form of organosolv lignin.

[0069] A peroxide within the meaning of the present invention is a compound comprising the peroxide anion O.sub.2.sup.2 or a peroxy group OO. Generally, a peroxide is a compound having the structure ROOR. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of 1. Examples of a peroxide include, but are not limited to, hydrogen peroxide (H.sub.2O.sub.2), inorganic peroxides and organic peroxides. Examples of inorganic peroxides include, but are not limited to, barium peroxide (BaO.sub.2), sodium peroxide (Na.sub.2O.sub.2), sodium percarbonate, sodium perborate. Examples of organic peroxides include, but are not limited to, compounds with the linkage COOC or COOH, such as tert-butylhydroperoxide, peracetic acid, m-chloroperbenzoic acid, dibenzoyl peroxide, diacyl peroxide or cumene hydroperoxide.

[0070] According to some embodiments, the peroxide is selected from the group consisting of hydrogen peroxide hydrogen peroxide, organic hydroperoxides, percarboxylic acids, organic peroxides, and diacyloyl peroxides. According to some embodiments, the peroxide is hydrogen peroxide.

[0071] The peroxide may be employed at any suitable amount, such as at in an amount of 5 to 40 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the peroxide is employed in an amount of 5 to 30 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the peroxide is employed in an amount of 6 to 8 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the peroxide is employed in an amount of 7 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the peroxide is employed in an amount of 20 to 30 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the peroxide is employed in an amount of 2 to 8 equivalents per aromatic ring of the aromatic compound.

[0072] According to some embodiments, the aromatic compound is lignin and the peroxide is employed in an amount of from 5 to 200 wt % per mass of lignin.

[0073] According to some embodiments, the peroxide is hydrogen peroxide employed as an aqueous solution in the range of 10% to 60%. According to some embodiments, the peroxide is hydrogen peroxide employed as an aqueous solution in the range of 20% to 40%. According to some embodiments, the peroxide is hydrogen peroxide employed as an aqueous solution in the range of 25% to 35%, such as a 30% aqueous solution.

[0074] According to some embodiments, the hydrogen peroxide is employed in an amount of 5 to 40 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the hydrogen peroxide is employed in an amount of 5 to 30 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the hydrogen peroxide is employed in an amount of 6 to 8 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the hydrogen peroxide is employed in an amount of 7 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the hydrogen peroxide is employed in an amount of 20 to 30 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the hydrogen peroxide is employed in an amount of 2 to 8 equivalents per aromatic ring of the aromatic compound.

[0075] It is also contemplated that the peroxide employed in accordance with the present invention is produced by a peroxidase, such as glucose oxidase, by electrolysis of water, by photocatalytic generation, or by catalytic process from oxygen.

[0076] The catalyst employed in accordance with the present invention may be any chemical compound (e.g., inorganic compound), which catalyses the oxidative cleavage of an aromatic compound, such as lignin or ferulic acid, to obtain vanillin or related compound. Non-limiting examples of suitable catalysts include vanadium compounds, copper compounds, cobalt compounds, nickel compounds, ruthenium compounds, ammonium compounds and sodium compounds.

[0077] According to some embodiments, the catalyst is selected from the group consisting of vanadium (II) oxide (vanadium monoxide, VO), Vanadium (III) oxide (vanadium trioxide, V.sub.2O.sub.3), Vanadium (IV) oxide (vanadium dioxide, VO.sub.2), Vanadium (V) oxide (vanadium pentoxide, V.sub.2O.sub.5), VO(AcAc).sub.2, VCl.sub.2, VOSO.sub.4, VOCl.sub.3, vanadates including VO.sub.3.sup. and VO.sub.4.sup.3 (such as Na.sub.3VO.sub.4 or NH.sub.4VO.sub.3), copper (II) bromide, ammonium metavanadate, copper (I) bromide, sodium molybdate, sodium orthovanadate, dicobalt octacarbonyl, nickel (II) chloride, and ruthenium (III) chloride.

[0078] According to some embodiments, the catalyst is a vanadium oxide, such as a vanadium oxide selected from the group consisting of Vanadium (II) oxide (vanadium monoxide, VO), Vanadium (III) oxide (vanadium trioxide, V.sub.2O.sub.3), Vanadium (IV) oxide (vanadium dioxide, VO.sub.2) and Vanadium (V) oxide (vanadium pentoxide, V.sub.2O.sub.5), VO(acac).sub.2, VCl.sub.2, VOSO.sub.4, VOCl.sub.3, vanadates including VO.sub.3 and VO.sub.4.sup.3 (such as Na.sub.3VO.sub.4 or NH.sub.4VO.sub.3). According to some embodiments, the vanadium oxide is Vanadium (V) oxide.

[0079] The catalyst may be employed at any suitable amount, such as in an amount of from 0.01 to 1 equivalents per aromatic ring of the aromatic compound. According to some embodiments, the catalyst is employed in an amount of 0.02 to 0.1, such as 0.05, equivalents per aromatic ring of the aromatic compound.

[0080] According to some embodiments, the catalyst is a vanadium oxide which is employed in amount of 0.02 to 0.1, such as 0.05, equivalents per aromatic ring of the aromatic compound.

[0081] According to some embodiments, the catalyst is a vanadium (V) oxide which is employed in amount of 0.02 to 0.1, such as 0.05, equivalents per aromatic ring of the aromatic compound.

[0082] According to some embodiments, the aromatic compound is lignin and the catalyst is employed in an amount of from 1 to 100 wt % per mass of lignin. According to some embodiments, the aromatic compound is lignin and the catalyst is employed in an amount of from 5 to 100 wt % per mass of lignin. According to some embodiments, the aromatic compound is lignin and the catalyst is employed in an amount of from 20 to 50 wt % per mass of lignin.

[0083] According to some embodiments, the aromatic compound is lignin and the catalyst is a vanadium oxide employed in an amount of from 1 to 100 wt % per mass of lignin, such as in an amount of from 20 to 50 wt % per mass of lignin.

[0084] According to some embodiments, the aromatic compound is lignin and the catalyst is a vanadium (V) oxide employed in an amount of from 1 to 100 wt % per mass of lignin, such as in an amount of from 20 to 50 wt % per mass of lignin.

[0085] Suitable, the reaction is carried out in in a suitable solvent. The solvent employed in accordance with the present invention may be any suitable solvent allowing the reaction to occur. Non-limiting examples of suitable solvents include dimethoxyethane (DME), acetonitrile (MeCN), ethanol (EtOH), tetrahydrofuran (TFA), methanol (MeOH), dichloromethane (DCM), heptane, ethyl acetate (EtOAc), diethyl ether, isopropanol, dimethyl carbonate (DMC), 2,2,2-trifluoroethanol (TFE). According to some embodiments, the solvent is dimethoxyethane (DME) or acetonitrile (MeCN). According to some embodiments, the solvent is dimethoxyethane (DME). According to some embodiments, the solvent is acetonitrile (MeCN). According to some embodiments, the solvent is 2,2,2-trifluoroethanol (TFE).

[0086] The reaction is carried out at any suitable temperature allowing the formation of vanillin, such as in the range of 0 C. to reflux temperature. According to some embodiments, the reaction is carried out at a temperature in the range of 10 C. to 60 C. According to some embodiments, the reaction is carried out at a temperature in the range of 10 C. to 30 C. According to some embodiments, the reaction is carried out at a temperature in the range of 15 C. to 60 C. According to some embodiments, the reaction is carried out at a temperature in the range of 15 C. to 30 C. According to some embodiments, the reaction is carried out at a temperature in the range of 20 C. to 60 C. According to some embodiments, the reaction is carried out at a temperature in the range of 20 C. to 30 C. According to some embodiments, the reaction is carried out at a temperature in the range of 20 C. to 25 C. According to some embodiments, the reaction is carried out at room temperature. According to some embodiments, the reaction is carried out at 60 C.

[0087] The reaction is carried out for any period of time suitable for the formation of vanillin or related product. Suitably, the reaction is carried out for at least 10 min. According to some embodiments, the reaction is carried out for at least 20 min. According to some embodiments, the reaction is carried out for at least 30 min. According to some embodiments, the reaction is carried out for at least 40 min. According to some embodiments, the reaction is carried out for at least 50 min. According to some embodiments, the reaction is carried out for at least 60 min. According to some embodiments, the reaction is carried out for at least 70 min. According to some embodiments, the reaction is carried out for at least 80 min. According to some embodiments, the reaction is carried out for at least 90 min. According to some embodiments, the reaction is carried out for at least 100 min. According to some embodiments, the reaction is carried out for at least 110 min. According to some embodiments, the reaction is carried out for at least 120 min.

[0088] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 24 hours. According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hour. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours. According to some embodiments, the reaction is carried out for a period of time in the range of 8 to 24 hours.

[0089] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. According to some embodiments, the reaction is carried out for a period of time in the range of 1 to 24 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C. According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. in DME. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in DME.

[0090] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. in TFE. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in TFE.

[0091] According to some embodiments, the reaction is carried out for a period of time in the range of 8 to 24 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in MeCN.

[0092] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant. According to some embodiments, the reaction is carried out for a period of time in the range of 1 to 24 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C. in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C. in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant.

[0093] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. in DME. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in DME in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant.

[0094] According to some embodiments, the reaction is carried out for a period of time in the range of 0.5 to 1 hours at 60 C. in TFE in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant. According to some embodiments, the reaction is carried out for a period of time in the range of 2 to 3 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in TFE in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant.

[0095] According to some embodiments, the reaction is carried out for a period of time in the range of 8 to 24 hours at room temperature, such as at a temperature in the range of 20 C. to 25 C., in MeCN in the presence of V.sub.2O.sub.5 as catalyst and hydrogen peroxide as oxidant.

[0096] The process may further comprise recovering vanillin and/or the related compound. Vanillin and/or the related compound may be recovered by any conventional method for isolation and/or purification chemical compounds from a reaction. Well-known purification procedures include centrifugation or filtration, precipitation, and chromatographic methods such as e.g. ion exchange chromatography, gel filtration chromatography, etc.

[0097] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples, which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.

EXAMPLES

Example 1Conversion of Ferulic Acid to Vanillin

[0098] Ferulic acid 1 was selected as model substrate to investigate the optimal reaction conditions. As a starting point for our research we investigated the influence of oxidation in the presence of different catalysts (Fe.sub.2O.sub.3, ZrBr.sub.2, (NH.sub.4).sub.2MoO.sub.4, RuCl.sub.3, NiCl.sub.2, CO.sub.2(CO).sub.8, Na.sub.3VO.sub.4, Na.sub.2MoO.sub.4, CuBr, NH.sub.4VO.sub.3, CuBr.sub.2, VOSO.sub.4.Math.H.sub.2O, VO(acac).sub.2, VCl.sub.2 and V.sub.2O.sub.5). The reaction was carried out using 10 mol % catalyst at room temperature for 2 h. Acetonitrile was used as solvent. During the investigation we found that a further conversion of vanillin 3 to vanillic acid 4 and 2-methoxy-1,4-benzoquinone 5 takes place.

##STR00004##

[0099] In the presence of vanadium, copper, cobalt, nickel, ruthenium, ammonium and sodium catalysts, ferulic acid 1 was converted into an intermediate product 2, vanillin 3 or one of the by-products (4, 5). The best conversion to the desired product vanillin 3 was achieved in the presence of V.sub.2O.sub.5.

[0100] Next, we investigated the influence of the amount of catalyst V.sub.2O.sub.5 on the conversion of ferulic acid 1 to vanillin 3. We tried to minimize the amount of catalyst. The results show that the amount of catalyst has no influence on the conversion. We obtained 68% of vanillin 3 when 0.01 to 1 equivalent of V.sub.2O.sub.5 was used. Further reactions were performed using 0.05 equivalents of catalyst V.sub.2O.sub.5.

TABLE-US-00001 TABLE 1 The oxidative cleavage of ferulic acid with 30% aq. H.sub.2O.sub.2 in MeCN. Vanillic Vanillin Intermediate acid Benzoquinone entry catalyst 3 [%] 2 [%] 4 [%] 5 [%] 1 Fe2O3 0 0 0 0 2 ZrBr2 0 0 0 0 3 (NH4)2MoO4 0 0 0 0 4 RuCl3 0 2 0 0 5 NiCl2 0 3 0 0 6 CO2(CO)8 0 8 0 0 7 Na2MoO4 0 17 0 0 8 Na3VO4 4 9 0 0 9 CuBr 11 10 0 0 10 NH4VO3 14 11 0 0 11 CuBr2 39 21 8 0 12 VO(acac)2 66 6 9 19 13 VOSO4H2O 57 15 15 12 14 VCl2 57 0 13 30 15 V2O5 68 0 8 24 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.7 mmol, 30%), catalyst (0.01 mmol), MeCN (1 mL), rt, 2 h. .sup.aConversion to product was determined by 1H NMR.
Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.7 mmol, 30%), catalyst (0.01 mmol), MeCN (1 mL), rt, 2 h. .sup.aConversion to product was determined by 1H NMR.

[0101] We have also tested various solvents such as acetonitrile (MeCN), ethanol (EtOH), dimethoxyethane (DME), tetrahydrofuran (THF), methanol (MeOH), dichloromethane (DCM), heptane, ethyl acetate (EtOAc), diethyl ether, isopropanol, dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), trifluoroacetic acid (TFA), water and 2,2,2-trifluoroethanol (TFE). DMSO, water and TFA are not suitable as solvents for the oxidative cleavage of the carbon-carbon double bond. The reaction was performed in the presence of TFE, DMC, isopropanol, diethyl ether, EtOAc, heptane, DCM, MeOH, THF, EtOH, MeCN or DME as solvent. The reaction was carried out quantitatively in ethanol, acetonitrile and DME. The best results were obtained in MeCN and DME, since ethyl vanillate was formed in 8% as a by-product in ethanol. In 2 h in DME as solvent the conversion to vanillin 3 was 95%.

TABLE-US-00002 TABLE 2 Oxidation of ferulic acid with 30% aq. H.sub.2O.sub.2 in different solvents. Vanillic Vanillin Intermediate aicd Benzoquinone entry solvent 3 [%] 2 [%] 4 [%] 5 [%] 1 H.sub.2O 0 0 0 0 2 TFA 0 0 0 0 3 DMSO 0 0 0 0 4 TFE 0 0 0 100 5 DMC 16 5 0 15 6 izopropanol 45 10 6 10 diethyl 7 ether 11 5 0 4 8 EtOAc 8 3 0 30 9 heptane 24 8 5 5 10 DCM 32 40 24 24 11 MeOH 28 22 22 9 12 THF 39 0 5 3 13 EtOH 59 0 11 22 14 MeCN 68 0 8 24 15 DME 95 5 0 0 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.7 mmol, 30%), catalyst (0.005 mmol), solvent (1 mL), rt, 2 h. .sup.aConversion to product was determined by .sup.1H NMR.

[0102] This series of experiments was carried out by varying the reaction times from 15 min to 24 h, while maintaining the amount of catalyst V.sub.2O.sub.5 (0.05 equiv.), the amount of 30% hydrogen peroxide solution (7 equiv.) and room temperature. The results (FIG. 5, Table 3) show the influence of the reaction time on the yield of the target product vanillin 3. When the oxidation reaction was performed out in 15 min, the yield of vanillin 3 was only 5%. In 2 h the yield increased to 100%, but an intermediate product 2 was still present in the reaction mixture. The reaction gave the best results in 3 hours. After 4 hours we got some acid (14%). A longer reaction time led to the formation of vanillic acid 4.

TABLE-US-00003 TABLE 3 Reaction profile for vanillin formation. Vanillic Vanillin Intermediate aicd Benzoquinone entry solvent 3 [%] 2 [%] 4 [%] 5 [%] 1 H.sub.2O 0 0 0 0 2 TFA 0 0 0 0 3 DMSO 0 0 0 0 4 TFE 0 0 0 100 5 DMC 16 5 0 15 6 izopropanol 45 10 6 10 7 diethyl ether 11 5 0 4 8 EtOAc 8 3 0 30 9 heptane 24 8 5 5 10 DCM 32 40 24 24 11 MeOH 28 22 22 9 12 THF 39 0 5 3 13 EtOH 59 0 11 22 14 MeCN 68 0 8 24 15 DME 95 5 0 0 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.7 mmol, 30%), catalyst (0.005 mmol), DME (1 mL), rt. .sup.aConversion to product was determined by .sup.1H NMR.

[0103] The reaction was further optimized by increasing the amount of hydrogen peroxide from 2 to 10 equivalents. The reaction with 7 equivalents was able to produce vanillin 3 in 100% yield. A further increase in hydrogen peroxide resulted in a lower product formation of vanillin 3 and an increase in the amount of acid 4. We also tried different concentrations of hydrogen peroxide. The reaction also takes place in the presence of 3% hydrogen peroxide and even at a higher concentration (60%). The best results were obtained with a 30% aqueous solution of hydrogen peroxide.

TABLE-US-00004 TABLE 4 Oxidation of ferulic acid with different amount of H.sub.2O.sub.2. equiv. of Vanillin Intermediate vanillic acid entry H.sub.2O.sub.2 3 [%] 2 [%] 4 [%] 1 2 22 8 0 2 3 23 8 0 3 5 54 9 0 4 7 100 0 0 5 7.sup.a 5 4 0 6 .sup.7.sup.b 10 4 0 7 7.sup.c 85 0 15 8 10 86 0 14 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.2-1.0 mmol, 30%), catalyst (0.005 mmol), DME (1 mL), rt, 3 h. .sup.aConversion to product was determined by .sup.1H NMR. .sup.aH.sub.2O.sub.2 (3%). .sup.bH.sub.2O.sub.2 (3%, time: 24 h). .sup.cH.sub.2O.sub.2 (60%).

[0104] We have also studied the influence of temperature on the implementation of the reaction. The results show that the higher temperature accelerates the conversion of the reaction. The reaction proceeds in the presence of less hydrogen peroxide and in a shorter time.

TABLE-US-00005 TABLE 5 Oxidation of CC double bond at 60 C. time Equiv. of Vanillin 3 Intermediate 2 vanillic acid 4 entry [h] H.sub.2O.sub.2 [%] [%] [%] 1 2 2.8 36 25 0 2 2 4.7 62 2 0 3 1 7 100 0 0 4 0.5 7 100 0 0 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.3-0.7 mmol, 30%), V.sub.2O.sub.5 (0.005 mmol), DME (1 mL), 60 C., time. .sup.aConversion to product was determined by .sup.1H NMR.

Preferred Procedure for Conversion of Ferulic Acid and Related Compounds to Vanillin and Corresponding Benzaldehydes

[0105] In a 10 mL volumetric flask, ferulic acid (0.5 mmol) and V.sub.2O.sub.5 catalyst (0.025 mmol) were added in a 5 mL solution of solvent DME. The hydrogen peroxide (30%, 7 equiv.) was first purged with argon and slowly added to a reaction mixture in three portions. The mixture was stirred at room temperature for 3 h. After completion of the reaction the reaction mixture was extracted with EtOAc (25 mL). The organic layer was dried over anhydrous Na.sub.2SO.sub.4 and evaporated under vacuum. The crude reaction was subjected to column chromatography with mobile phase EtOAc/heptane (2/1). The solvent was evaporated in vacuo to provide vanillin (91%).

Example 2Conversion of Ferulic Acid Model Compounds to Corresponding Benzoic Acids

[0106] Cinnamic acid 1 was taken as a model substrate, and several reaction conditions were studied to achieve oxidation to benzoic acid 4.

##STR00005##

[0107] The results in FIG. 6 and Table 6 show the influence of the amount of hydrogen peroxide on the conversion of cinnamic acid 1 to benzoic acid 4. We tested the amount of hydrogen peroxide from 0 to 28 equivalents. The best results were obtained with 28 equivalents of 30% hydrogen peroxide.

TABLE-US-00006 TABLE 6 The effect of the amount of hydrogen peroxide on the oxidative cleavage of CC double bond. Equiv. of Cinnamic acid Benzaldehyde Benzoic acid entry H.sub.2O.sub.2 1 [%] 3 [%] 4 [%] 1 0 100 0 0 2 4 88 6 6 3 7 84 6 10 4 9 80 12 8 5 15 69 13 18 6 19 27 0 73 7 23 10 0 90 8 28 0 0 100 Reaction conditions: cinnamic acid 1 (0.1 mmol), H.sub.2O.sub.2 (0.0-2.8 mmol, 30%), catalyst (0.005 mmol), MeCN(1 mL), rt, 24 h. .sup.aConversion to product was determined by .sup.1H NMR.

[0108] FIG. 7 and Table 7 show the effect of the reaction time on the yield of the target product benzoic acid 4. The influence of the reaction time was also tested. When the oxidation reaction was carried out in 1 h, the yield was only 9%. The reaction gave the best results in 24 hours, the cinnamic acid was completely converted into the desired product.

TABLE-US-00007 TABLE 7 Reaction profile for benzoic acid formation. Time Cinnamic acid 1 Benzaldehyde 3 Benzoic acid 4 entry [h] [%] [%] [%] 1 0.5 100 0 0 2 1 91 0 9 3 3 30 3 67 4 5 22 7 71 5 8 14 0 86 6 24 0 0 100 Reaction conditions: cinnamic acid 1 (0.1 mmol), H.sub.2O.sub.2 (2.8 mmol, 30%), catalyst (0.005 mmol), MeCN (1 mL), rt, time. .sup.aConversion to product was determined by .sup.1H NMR.

Preferred Procedure for Conversion Cinnamic Acid and Related Compounds to Benzoic Acid and Corresponding Aromatic Carboxylic Acids

[0109] In a 10 mL volumetric flask, substrate (0.5 mmol) and V.sub.2O.sub.5 catalyst (0.025 mmol) were added in a 5 mL solution of solvent MeCN. The hydrogen peroxide (30%, 28 equiv.) was first purged with argon and slowly added to a reaction mixture in three portions. The mixture was stirred for 24 h at room temperature. After completion of the reaction, the reaction mixture was extracted with EtOAc (25 mL). The organic layer was dried over anhydrous Na.sub.2SO.sub.4 and evaporated under vacuum. The crude reaction was subjected to column chromatography with mobile phase EtOAc/heptane (2/1). The solvent was evaporated in vacuo to provide the product benzoic acid (94%).

Example 3Conversion of Lignin to Vanillin

[0110] Lignin samples were obtained as aqueous solution after kraft pulp production of softwood materials. The conversion of lignin to vanillin was carried out according to an optimized process for the conversion of ferulic acid to vanillin. We used V.sub.2O.sub.5 as catalyst and DME as solvent. The reaction was carried out at room temperature. We investigated the influence of reaction time and hydrogen peroxide amount on the conversion of lignin to vanillin. The best results were achieved with 50 wt % of hydrogen peroxide in 2 h.

TABLE-US-00008 TABLE 8 Conversion of lignin to vanillin. Time H.sub.2O.sub.2 vanillin 3 benzoquinone 5 entry [h] [wt %] [%] [%] 1 0.25 50 0 0 2 0.5 50 7 1 3 0.75 50 10 2 4 1 50 18 18 5 2 50 83 17 6 2 10 3 2 7 2 75 71 29 8 2 125 48 52 9 .sup.1.sup.b 50 48 52 Reaction conditions: lignin (100 mg), H.sub.2O.sub.2 (10-125 wt %, 30%), catalyst (5 wt %), DME (1 mL), rt, time. .sup.aConversion to product was determined by .sup.1H NMR. .sup.bsolvent: MeCN.

[0111] Preferred Procedure for Conversion of Lignin to Vanillin 50 ml of black liquor of lignin were placed in Erlenmeyer flask with magnetic stirrer. Concentrated H.sub.2SO.sub.4 was added to lower the pH value to 2. The mixture was stirred for 10 minutes at room temperature. After completion of the precipitation process, the sample was filtered through a Bchner funnel and the filtrate was collected (lignin yield: 16 g/L). In a 5 mL volumetric flask, softwood lignin (100 mg) and V.sub.2O.sub.5 catalyst (5 wt %) were added in a 2 mL solution of solvent DME. The hydrogen peroxide (30%, 250 L) was first purged with argon and slowly added to a reaction mixture. The mixture was stirred for 2 h at room temperature. After completion of the reaction, the reaction mixture was extracted with EtOAc (25 mL). The organic layer was dried over anhydrous Na.sub.2SO.sub.4 and evaporated under vacuum. The crude reaction was subjected to column chromatography with mobile phase EtOAc/heptane (2/1). The solvent was evaporated in vacuo to provide the product vanillin (6.1%).

Example 4Conversion of 4-Hydroxycinnamic Acid Derivatives to Benzoquinones

[0112] We have also developed a process for the synthesis of benzoquinones. We investigated the effect of different solvents on the conversion of ferulic acid to 2-methox-1,4-benzoquinone. The results show that the reactions occur quantitatively in TFE as solvent in the presence of V.sub.2O.sub.5 catalyst and hydrogen peroxide as oxidant.

TABLE-US-00009 TABLE 9 Oxidation of ferulic acid to 2-methoxy-1,4-benzoquinone 2-methoxy-1,4- vanillin Vanillic acid benzoquinone entry solvent 3 [%] 4 [%] 5 [%] 1 THF 39 5 3 2 diethyl ether 11 0 4 3 heptane 24 5 5 4 MeOH 28 22 9 5 izopropanol 45 6 10 6 DMC 16 0 15 7 EtOH 59 11 22 8 DCM 32 24 24 9 MeCN 68 8 24 10 EtOAc 8 0 30 11 TFE 0 0 100 Reaction conditions: ferulic acid (0.1 mmol), H.sub.2O.sub.2 (0.7 mmol, 30%), V.sub.2O.sub.5 (0.005 mmol), solvent (1 mL), rt, 2 h. .sup.aConversion to product was determined by .sup.1H NMR
Preferred Procedure for Synthesis of 2-Methoxy-1,4-Benzoquinone from Ferulic Acid

[0113] In a 5 mL volumetric flask, ferulic acid (0.2 mmol) and V.sub.2O.sub.5 catalyst (0.01 mmol) were added in a 2 mL solution of solvent TFE (2,2,2-trifluoroethanol). The hydrogen peroxide (30%, 7 equiv.) was first purged with argon and slowly added to a reaction mixture. The mixture was stirred at room temperature for 2 h. After completion of the reaction the reaction mixture was extracted with EtOAc (23 mL). The organic layer was dried over anhydrous Na.sub.2SO.sub.4 and evaporated under vacuum to provide 2-methoxy-1,4-benzoquinone (84%).

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