METHOD OF DEPOLYMERIZING LIGNIN

Abstract

A method of depolymerizing lignin and to the use of this method in the production of fuels, electronic components, plastic polymers, rubber, medicines, vitamins, cosmetic products, perfumes, foodstuffs, synthetic threads and fibres, synthetic leathers, adhesives, pesticides and fertilizers is provided. It also relates to a method of producing fuels, electronic components, plastic polymers, rubber, medicines, vitamins, cosmetic products, perfumes, foodstuffs, synthetic threads and fibres, synthetic leathers, adhesives, pesticides and fertilizers, including a step of depolymerizing lignin using the method according to the invention.

Claims

1. A method of depolymerizing lignin to molecules containing 1 or 2 aromatic rings, comprising selectively cleaving of the sp.sup.3 carbon-oxygen bond of the alkaryl ethers of the -O-4, -O-4, -5, -1, - type present in lignin, wherein a lignin with a level of sulfur below 1.5 wt %, relative to the total weight of the lignin, is reacted, in the presence of a catalyst, with a silane compound of formula (I) ##STR00010## in which R.sup.1, R.sup.2 and R.sup.3 represent, independently of one another, a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, a silylated group, a siloxy group, an aryl group, an amino group, said alkyl, alkenyl, alkynyl, alkoxy, silylated, siloxy, aryl and amino groups optionally being substituted, or R.sup.3 is as defined above and R.sub.1 and R.sub.2, taken together with the silicon atom to which they are bound, form a silylated heterocycle, optionally substituted.

2. The method as claimed in claim 1, wherein the level of sulfur in the lignin is greater than or equal to zero and remains below 1.5 wt %, relative to the total weight of the lignin, as defined below:
0level of sulfur in the lignin<1.5 wt %, relative to the total weight of lignin.

3. The method as claimed in claim 1, wherein the lignin is extracted from a plant species selected so as to have: at least 10 wt % of lignin relative to the total weight of the sample of the plant species selected; at least 30% of cleavable bonds relative to the total number of bonds present between the monomer units in the lignin; and at least 50% of residue G, H or S of the total number of residues present in the lignin used.

4. The method as claimed in claim 1, wherein the aromatic molecules containing 1 or 2 aromatic rings have an average molar mass by weight below 1500 g/mol for the molecules in silylated form or an average molar mass by weight less than or equal to 450 g/.

5. The method as claimed in claim 1, wherein the silane compound of formula (I), R.sup.1, R.sup.2 and R.sup.3 represent, independently of one another, a hydrogen atom; an alkyl group selected from the methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl groups and their branched isomers; an alkoxy group whose alkyl group is selected from the methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl groups and their branched isomers; an aryl group selected from the benzyl and phenyl groups; a silylated group selected from polydimethylsiloxane (PDMS) and polymethylhydroxysiloxane (PMHS) and tetramethyldisiloxane (TMDS).

6. The method as claimed in claim 1, wherein the catalyst is an organic catalyst selected from: carbocations selected from the trityl cation ((C.sub.6H.sub.5).sub.3C.sup.+), tropilium (C.sub.7H.sub.7).sup.+, benzyl cation (C.sub.6H.sub.5CH.sub.2.sup.+), ally! cation (CH.sub.3CH.sup.+CHCH.sub.2), methylium (CH.sub.3.sup.+), cyclopropylium (C.sub.3H.sub.5.sup.+), the cyclopropyl carbocation selected from the dimethyl cyclopropyl carbocation and the dicyclopropyl carbocation, acylium (R.sup.1CO).sup.+with R.sup.1 selected from methyl, propyl and benzyl, the benzenium cation (C.sub.6H.sub.5).sup.+, and the norbornyl cation (C.sub.7H.sub.11).sup.+; oxoniums selected from (CH.sub.3).sub.3O.sup.+BF.sub.4.sup. and (CH.sub.3CH.sub.2).sub.3O.sup.+BF.sub.4.sup.; a silylium ion (R.sup.1).sub.3Si.sup.+ selected from Et.sub.3Si.sup.+ and Me.sub.3Si.sup.4+, wherein R1 is a hydrogen atom, a halogen atom, a hydroxyl group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, a silylated group, a siloxy group, an aryl group, an amino group, said alkyl, alkenyl, alkynyl, alkoxy, silylated, siloxy, aryl and amino groups optionally being substituted; disilyl cations having a bridging hydride selected from the formulas shown below ##STR00011## with the counterion of said silylium ion, of said carbocations and of said disilyl cations being a halide selected from F.sup., Cl.sup., Br.sup. and I.sup.; or an anion selected from BF.sub.4.sup., SbF.sub.6.sup., B(C.sub.6F.sub.5).sub.4.sup., B(C.sub.6F.sub.5).sub.4.sup., CF.sub.3SO.sub.3.sup., PF.sub.6.sup..

7. The method as claimed in claim 1, wherein the catalyst is an organometallic catalyst selected from: the iridium complexes of formula (III) ##STR00012## in which R.sup.6 represents an alkyl or aryl group; R.sup.7 represents a hydrogen atom or an alkyl group; and X.sup.2 represents a CH.sub.2 group or an oxygen atom; Y represents a counterion selected from B(C.sub.6F.sub.5).sub.4 and B(C.sub.6H.sub.5).sub.4; S represents a molecule of solvent, coordinated to the complex, selected from dimethylsulfoxide (DMSO), acetonitrile (CH.sub.3CN) and acetone (CH.sub.3COCH.sub.3); and the ruthenium complexes of formula (V) ##STR00013## in which R.sup.12 represents a hydrogen atom or an alkyl group; R.sup.13 represents an aryl or an alkyl group, said aryl and alkyl groups optionally being substituted; Z represents a CH.sub.2 group, an oxygen atom or a sulfur atom; A.sup. represents a counterion selected from B(C.sub.6F.sub.5).sub.4.sup. and [CHB.sub.11H.sub.5Cl.sub.6].sup..

8. The method as claimed in claim 1, wherein the organometallic catalyst is selected from the iridium complex [(POCOP)Ir(H)(acetone)].sup.+B(C.sub.6F.sub.5).sub.4.sup. with (POCOP) representing 2,6-bis(di-tert-butylphosphinito)phenyl; and the ruthenium complex of formula (V) in which R.sup.12 represents a methyl group; R.sup.13 represents p-FC.sub.6H.sub.4; Z represents a sulfur atom; A.sup. represents B(C.sub.6F.sub.5).sub.4.

9. The method as claimed in claim 1, wherein the catalyst is of the Lewis acid type selected from: boron compounds selected from BF.sub.3, BF.sub.3(Et.sub.2O), BCl.sub.3, BBr.sub.3, triphenyl hydroborane, tricyclohexyl hydroborane, B(C.sub.6F.sub.5).sub.3, B-methoxy-9-borabicyclo[3.3.1]nonane (B-methoxy-9-BBN), B-benzyl-9-borabicyclo[3.3.1]nonane (B-benzyl-9-BBN); borenium compounds Me-TBD-BBN.sup.+, the borenium ferrocene derivatives corresponding to formula ##STR00014## in which R.sup.1 is a phenyl group and R.sup.3 is 3,5-dimethylpyridyl; aluminum compounds selected from AlCl.sub.3, AlBr.sub.3, aluminum isopropoxide Al(O-i-Pr).sub.3, aluminum ethanoate (Al(C.sub.2H.sub.3O.sub.2)), Krossing's salt [Ag(CH.sub.2Cl.sub.2)]{Al[OC(CF.sub.3).sub.3].sub.4}, Li{Al[OC(CF.sub.3).sub.3].sub.4}, Et.sub.2Al.sup.+; indium compounds selected from InCl.sub.3, In(OTf).sub.3; iron compounds selected from FeCl.sub.3, Fe(OTf).sub.3; tin compounds selected from SnC.sub.14, Sn(OTf).sub.2; phosphorus compounds such as PCl.sub.3, PCl.sub.5, POCl.sub.3; trifluoromethanesulfonate or triflate compounds (CF.sub.3SO.sub.3.sup.) of transition metals and lanthanides selected from scandium triflate, ytterbium triflate, yttrium triflate, cerium triflate, samarium triflate, neodymium triflate.

10. The method as claimed in claim 1, wherein the catalyst is selected from BF.sub.3; InCl.sub.3; triphenylcarbenium tetrakis(perfluorophenyl)borate [(Ph).sub.3C.sup.+B(C.sub.6F.sub.5).sub.4.sup.,B(C.sub.6F.sub.5).sub.3].

11. The method as claimed in claim 1, wherein the reaction is carried out under a pressure of an inert gas or a mixture of inert gases selected from nitrogen and argon, or gases generated by the process, notably methane and hydrogen, said pressure being between 0.2 and 50 bar, inclusive.

12. The method as claimed in claim 1, wherein the reaction is carried out at a temperature between 0 and 150 C., inclusive.

13. The method as claimed in claim 1, wherein the reaction is carried out in a solvent or a mixture of at least two solvents selected from: silylated ethers selected from 1,1,1,3,3,3-hexamethyldisiloxane ((Me.sub.3Si).sub.2O), 1,1,1,3,3,3-hexaethyldisiloxane ((Et.sub.3Si).sub.2O); hydrocarbons selected from benzene, toluene, pentane and hexane; sulfoxides selected from dimethylsulfoxide (DMSO); alkyl halides selected from chloroform, methylene chloride, chlorobenzene, dichlorobenzene.

14. The method as claimed in claim 1, wherein the weight ratio of the silane compound of formula (I) to the lignin is between 0.5 and 6, inclusive.

15. The method as claimed in claim 1, wherein the amount of catalyst is from 0.001 to 1 equivalent by weight, inclusive, relative to the initial weight of lignin.

16. The use of a method of depolymerizing lignin as claimed in claim 1, in the manufacture of fuels, electronic components, plastics, rubber, medicinal products, vitamins, cosmetics, perfumes, food products, synthetic yarn and fibers, synthetic leather, adhesives, pesticides, and fertilizers.

Description

EXAMPLES

[0162] The method of depolymerizing lignin by selective cleavage of the sp.sup.3 carbon-oxygen bond of the alkaryl ethers present in lignin is carried out in the presence of a catalyst, by reacting a lignin with a level of sulfur below 1.5 wt % of lignin, with a silane compound of formula (I) according to the following experimental protocol.

[0163] The reactants used, notably the silane compound of formula (I) and the catalyst, are commercial products.

General Experimental Protocol for Depolymerization of Lignin

[0164] 1. Under an inert atmosphere of argon or nitrogen, the silane compound of formula (I), the catalyst (from 1 to 0.001 equivalents by weight calculated relative to the initial weight of lignin added) and half the amount of solvent are stirred in a glass vessel of suitable volume. The concentration of silane in the reaction mixture is in the range 1.0-6.0 mol.Math.L.sup.1 (concentration calculated on the basis of half the final volume of solvent introduced). [0165] 2. In addition, in a Schlenk tube, organosolv lignin (10-40% of equivalent by weight of silane added), previously dried overnight using a vacuum manifold, is stirred with the remaining half of solvent. [0166] 3. The solution containing the catalyst and the silane compound of formula (I) is added slowly (addition time 15 minutes to 1 hour), using a syringe and with stirring, to the Schlenk tube. The latter is left open for evacuating the gases produced by the reaction. [0167] 4. After the end of adding the solution, and when release of gases has stopped, the Schlenk tube is closed and is stirred. The starting lignin is then almost completely soluble. The reaction is monitored by GC-MS. [0168] 5. Once the reaction has ended (reaction time from 1 to 72 hours), the solvent as well as the volatile compounds are evaporated using a vacuum manifold (10.sup.2 mbar). The viscous liquid obtained is purified by silica gel chromatography using an elution gradient from 100:0 to 0:100 of pentane: CH.sub.2Cl.sub.2 for the nonpolar fractions, and an elution gradient from 100:0 to 0:100 of CH.sub.2Cl.sub.2:EtOAc for the polar fractions. When a fraction is very polar, elution may be performed with EtOAc:MeOH H mixture (50:50 to 0:100). It should be noted that depending on the intended application, the purification step may or may not be omitted. [0169] 6. Finally, the various fractions from the column are hydrolyzed in an acid medium using HCl or H.sub.2SO.sub.4 2M in THF, or in a basic medium using NaOH or KOH 15 to 30 wt %, or finally using a fluorinated reactant of the type: HF-pyridine, TBAF, CsF, NH.sub.4F to give the corresponding hydrolyzed product.

[0170] A set of results is presented below, giving examples of depolymerization of organosolv lignin.

[0171] The catalysts tested are B(C.sub.6F.sub.5).sub.3 as well as the iridium complex ([(POCOP)Ir(H)(acetone)].sup.+B(C.sub.6F.sub.5).sub.4.sup.) whose synthesis is described by I. Gottker-Schnetmann, P. White, and M. Brookhart, J. Am. Chem. Soc. 2004, 126, pages 1804-1811; and by J. Yang and M. Brookhart, J. Am. Chem. Soc. 2007, 129, pages 12656-12657.

[0172] The lignin used is obtained from several methods of the organosolv type {a) Alcell: J. H. Lora, W. G. Glasser, J Polym Environ, 2002, 10, pages 39-48; b) Acetocell: Bojan Jankovic, Bioresource Technol., 2011, 102, pages 9763-9771; c) Acetosolv: J. C. Parajo, J. L. Alonso, D. Vazquez, Bioresource Technology, 1993, 46, pages 233-240; d) ASAM: I. Miranda, H. Pereira, Holzforschung, 2002, 56, pages 85-90; e) Batelle/Genevaphenol: A. Johansson, O. Aaltonen, P. Ylinen, Biomass 1987, 13, pages 45-65; f) Formacell: X. F. Sun, R. C. Sun, P. Fowler, M. S. Baird, Carbohydr. Polym., 2004, 55, pages 379-391; g) Milox: P. Ligero, A. Vega, J. J. Villaverde, Bioresource Technol., 2010, 101, pages 3188-3193; h) Organocell: A. Lindner, G. Wegener, J. Wood Chem. Technol. 1988, 8, pages 323-340} and in particular the AVIDEL process (described by H. Q. Lam, Y. Le Bigot, M. Delmas, G. Avignon, Industrial Crops and Products, 2001, 14, pages 139-144), which constitutes an optimized version of the Formacell method.

[0173] The types of wood from which the lignins are obtained are selected with different G/H/S proportions, and in addition a mixture of several types of wood was used, to demonstrate the versatility and robustness of the method. In the context of the invention, robustness of the method means a method which, in very mild operating conditions, allows cleavage of the chemical functions that are usually very difficult to cleave.

Example 1

Depolymerization of Lignin Obtained from London Plane (Platanus acerifolia) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0174] The depolymerization of London plane is carried out following the general procedure for depolymerization described above.

[0175] Depolymerization is carried out with 4-5 mol.Math.L.sup.1 Et.sub.3SiH as silane (concentration calculated on the basis of half the final volume of solvent introduced). The weight of lignin added corresponds to 30% of the weight of silane added and the solvent used is dichloromethane (CH.sub.2Cl.sub.2). The reaction takes place in the presence of 20-30 wt % of catalyst (weight calculated relative to the weight of lignin added). The catalyst used is B(C.sub.6F.sub.5).sub.3.

[0176] The solution of silane and catalyst is added to the Schlenk tube over a period of 30 minutes and the reaction is stirred for 24 hours at 25 C. After the end of the reaction and evaporation of the solvent and volatiles, the viscous liquid obtained is purified using the same conditions as described above. This liquid consists of a mixture of products of formulas IIa, IIb, IIe and IId (identified by NMR and GC-MS).

##STR00008##

[0177] The molar ratio IIa/IIb/IIe/IId was determined according to GC-MS analysis (apparatus Shimadzu GCMS-QP2010 Ultra gas chromatograph mass spectrometer equipped with a fused silica capillary column Supelco SLB-ms (30 m0.25 mm0.25 m) as indicated in Table 1. Finally, the fractions from purification were hydrolyzed in an acid medium using a 2M HCl solution in THF. After stirring for 16 hours at room temperature (20+5 C.), the solvent and the volatiles are evaporated, giving the various corresponding polyols.

IIa:

[0178] .sup.1H NMR (200 MHz, CDCl.sub.3, Me.sub.4Si) (ppm)=6.71 (1H, d, .sup.3J=8.1 Hz, ArH), 6.63 (1H, s, ArH), 6.58 (1H, d, .sup.3J=8.1 Hz, ArH), 2.45 (2H, t, .sup.3J=7.8 Hz, ArCH.sub.2), 1.57 (2H, sex, .sup.3J=7.8 Hz, CH.sub.2CH.sub.3), 0.98 (18H, t, .sup.3J=7.9 Hz, CH.sub.3CH.sub.2Si), 0.90 (3H, t, .sup.3J=7.8 Hz, CH.sub.3CH.sub.2Si), 0.74 (12H, q, .sup.3J=7.9 Hz, CH.sub.3CH.sub.2Si).

[0179] .sup.13C NMR (50 MHz, CDCl.sub.3, Me.sub.4Si): (ppm)=146.5, 144.7, 136.0, 121.3, 120.9, 120.2, 37.4, 24.7, 13.9, 6.9, 5.3, 5.2.

[0180] HR-MS (APPI): calculated (M+) (C.sub.21H.sub.40O.sub.2Si.sub.2), m/z 380.2566; found (M+), m/z 380.2559.

[0181] Anal. Calculated. for C.sub.21H.sub.40O.sub.2Si.sub.2 (molecular weight 380.72): C, 66.25; H, 10.59.

[0182] Found: C, 66.18; H, 10.46.

[0183] MS: IE (m/z): 380 (9); 351 (4); 207 (8); 117 (4); 116 (11); 115 (100); 88 (7); 87 (74); 59 (45); 58 (4).

IIb:

[0184] .sup.1H NMR (200 MHz, CDCl.sub.3, Me.sub.4Si) (ppm)=6.79-6.50 (3H, m, ArH), 3.60 (2H, t, .sup.3J=6.6 Hz, CH.sub.2O), 2.54 (2H, t, .sup.3J=7.6 Hz, ArCH.sub.2), 1.79 (2H, quin, .sup.3J=7.0 Hz, ArCH.sub.2CH.sub.2), 1.05-0.88 (27H, m, CH.sub.3CH.sub.2Si), 0.84-0.48 (18H, m, CH.sub.3CH.sub.2Si).

[0185] .sup.13C NMR (50 MHz, CDCl.sub.3, Me.sub.4Si): (ppm)=146.5, 144.8, 135.4, 121.3, 120.9, 120.3, 62.3, 34.7, 31.5, 6.9, 6.8, 5.2, 5.2, 4.6.

[0186] MS: IE (m/z): 87 (100), 115 (57), 59 (38), 89 (28), 207 (24), 32 (16), 235 (11), 88 (10), 337 (9), 511 (8), 116 (6), 86 (6).

IIc:

[0187] .sup.1H NMR (200 MHz, CDCl.sub.3, Me.sub.4Si) (ppm)=6.27 (2H, s, ArH), 2.39 (2H, t, .sup.3J=7.5 Hz, ArCH.sub.2), 1.69-1.45 (2H, m, CH.sub.2CH.sub.3), 1.1-0.84 (27H, m, CH.sub.3CH.sub.2Si), 0.90-0.81 (3H, m, CH.sub.3CH.sub.2Si), 0.83-0.65 (18H, m, CH.sub.3CH.sub.2Si).

[0188] .sup.13C NMR (50 MHz, CDCl.sub.3, Me.sub.4Si): (ppm)=147.8, 146.5, 134.5, 113.6, 37.7, 24.6, 13.7, 7.0, 6.8, 5.4, 5.2.

[0189] MS: IE (m/z): 510 (8); 339 (4); 338 (10); 337 (31); 116 (7); 115 (60); 88 (10); 87 (100); 86 (4); 59 (49).

IId:

[0190] .sup.1H NMR (200 MHz, CDCl.sub.3, Me.sub.4Si) (ppm)=6.28 (2H, s, ArH), 3.59 (2H, t, .sup.3J=6.7 Hz, CH.sub.2O), 2.48 (2H, t, .sup.3J=7.5 Hz, ArCH.sub.2), 1.78 (2H, quin, .sup.3J=7.3 Hz, ArCH.sub.2CH.sub.2), 1.13-0.85 (36H, m, CH.sub.3CH.sub.2Si), 0.84-0.49 (24 H, m, CH.sub.3CH.sub.2Si).

[0191] .sup.13C NMR (50 MHz, CDCl.sub.3, Me.sub.4Si): (ppm)=147.9, 136.6, 134.0, 113.6, 62.3, 34.6, 31.7, 6.9, 6.8, 5.4, 5.2, 4.5.

[0192] MS: IE (m/z): 87 (100), 115 (36), 59 (32), 89 (19), 641 (9), 88 (9), 467 (8), 365 (7), 337 (6), 642 (5), 640 (5), 116 (4).

Example 2

Depolymerization of Lignin from Pine (Pinus pinea) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0193] The same procedure as used for depolymerization of lignin from London plane is used for depolymerization of lignin from pine. In this case, after purification, the product IIa is obtained with very high purity (>99.7%) with a yield by weight from 10 to 20% relative to the weight of lignin used (not optimized). This product was characterized by GC-MS, .sup.13C NMR, .sup.1H NMR and HR-MS. Finally, the fractions from purification are hydrolyzed by stirring each fraction at 25 C. for 16 h in the presence of a 2M HCl solution in THF. Finally, the polyols are obtained after evaporation of the solvent and the volatile compounds.

Example 3

Depolymerization of Lignin Obtained from Lombardy Poplar (Populus nigra) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0194] The same procedure as used for depolymerization of lignin from London plane is used for depolymerization of lignin from Lombardy poplar. Moreover, the products obtained in both cases are similar. Among the most volatile products, the products of formulas IIa and IIc are identified by NMR and GC-MS as indicated in Table 1.

Example 4

Depolymerization of Lignin Obtained from Silver Birch (Betula pendula) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0195] The same procedure as used for depolymerization of lignin from London plane is used for depolymerization of lignin from silver birch. Moreover, the products obtained in both cases are similar. Among the most volatile products, the products of formulas IIa and IIe are identified by NMR and GC-MS as indicated in Table 1.

Example 5

Depolymerization of Lignin Obtained from Common Beech (Fagus sylvatica) (Extracted by the AVIDEL process) Using Triethylsilane (Et.SUB.3.SiH)

[0196] The same procedure as used for depolymerization of lignin from London plane is used for depolymerization of lignin from common beech. Moreover, the products obtained in both cases are similar. Among the most volatile products, the products of formulas IIa and IIe are identified by NMR and GC-MS as indicated in Table 1.

Example 6

Depolymerization of Lignin Obtained from Eucalyptus (Eucalyptus camaldulensis) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0197] The same procedure as used for depolymerization of lignin from common beech is used for depolymerization of lignin from eucalyptus. Moreover, the products obtained in both cases are similar. Among the most volatile products, the products of formulas IIa, IIb, IIe and IId are identified by NMR and GC-MS. The IIc/IIa molar ratio is 76/24 respectively according to GC-MS analysis.

Example 7

Depolymerization of Lignin Obtained from Western Red Cedar (Thuja plicata) (Extracted by the AVIDEL Process) Using Triethylsilane (Et.SUB.3.SiH)

[0198] The same procedure as used for depolymerization of lignin from eucalyptus (Eucalyptus camaldulensis) is used for depolymerization of lignin from western red cedar. Moreover, the products obtained in both cases are similar. Among the most volatile products, the products of formulas IIa and IIb were identified by NMR and GC-MS as indicated in Table 1.

Example 8

Depolymerization of Lignin Obtained from F315 Sawdust Mixture (Extracted by the AVIDEL Process) Using Tetramethyldisiloxane (TMDS)

[0199] Depolymerization of lignin is carried out with lignin obtained from F315 sawdust mixture (sawdust mixture marketed by the company SPPS extracted from species belonging to the family Pinaceae).

[0200] When TMDS (tetramethyldisiloxane) is used as silane, there is a possibility of formation of gel, which makes the reaction very difficult. In this case two solutions may be envisaged: dilution of the solution 3 to 4 times using CH.sub.2Cl.sub.2 as solvent or else use of benzene or toluene as solvent. However, reaction will be slower in both cases envisaged. If reaction takes place in CH.sub.2Cl.sub.2, the concentration of TMDS is of the order of 1-3 mol.Math.L.sup.1 (concentration calculated on the basis of half the final volume of solvent introduced). 20 wt % of B(C.sub.6F.sub.5).sub.3 (weight calculated relative to the weight of lignin added) is required for catalyzing the reaction. The weight of lignin added is between 10 and 30% of the weight of silane added. Addition of the catalyst-silane mixture takes from 30 to 45 min. Then the reaction is stirred for 24 hours at 25 C.

[0201] After the end of the reaction, the volatile compounds as well as the solvent are evaporated under vacuum (10.sup.2 mbar). The mixture resulting from depolymerization degrades during purification on a silica column and the product obtained is hydrolyzed in a basic medium, using a mixture of THF and H.sub.2O containing 10 wt % of NaOH. After 16 hours of stirring at 25 C., the volatile compounds as well as the solvents are evaporated, and the product is purified on a silica column. Hydrolysis of the mixture leads to products of formula (IV).

Example 9

Depolymerization of Lignin Obtained from the Commercial F315 Sawdust Mixture (Extracted by the AVIDEL Process) Using ([(POCOP)Ir(H)(acetone)].SUP.+.B(C.SUB.6.F.SUB.5.).SUB.4..SUP..) and Triethylsilane (Et.SUB.3.SiH)

[0202] Depolymerization of lignin obtained from F315 sawdust mixture (sawdust mixture marketed by the company SPPS extracted from species belonging to the family Pinaceae) is carried out following the general operating protocol for depolymerization described above.

[0203] When the ([(POCOP)Ir(H)(acetone)].sup.+B(C.sub.6F.sub.5).sub.4.sup.) complex is used for lignin depolymerization, the procedure is similar to that in which the catalyst used is B(C.sub.6F.sub.5).sub.3. Et2SiH.sub.2 (5 mol.Math.L.sup.1) is used as silane in chlorobenzene. The weight of the lignin corresponds to 30% of the weight of silane added. The reaction takes place in the presence of 25 wt % of catalyst (weight calculated relative to the weight of lignin added). Addition of the silane and catalyst takes 30 min. The reaction time is of the order of 24 hours. Then the solvent and the volatiles are evaporated, and the viscous liquid obtained is purified on a silica column (see general procedure). The products from the column are hydrolyzed by stirring the products for 16 hours in a 2M HCl solution in THF. Finally, the various corresponding polyols are obtained by evaporation of the solvent and volatiles under vacuum. Hydrolysis of the mixture leads to products of formula (IV).

Example 10

Depolymerization of Lignin Obtained from F315 Sawdust Mixture (Rich in G Unit) (Extracted with Ethanol) with Triethylsilane (Et.SUB.3.SiH)

[0204] Lignin obtained from F315 sawdust mixture (sawdust mixture marketed by the company SPPS extracted from species belonging to the family Pinaceae) was extracted with ethanol in the presence of a catalytic amount of hydrochloric acid, by the method described by S. Bauer, H. Sorek, V. D. Mitchell, A. B. Ibez, D. E. Wemmer, J. Agric. Food Chem. 2012, 60, pages 8203-8212.

[0205] The same procedure as used for depolymerization of lignin from plane is used. This method leads to complete dissolution of the lignin as well as production of a mixture of products.

[0206] Among the most volatile products, IIa and IIb are identified by NMR and GC-MS as indicated in Table 1. Hydrolysis of the mixture leads to products of formula (IV).

Example 11

Depolymerization of Lignin Obtained from F315 Sawdust Mixture (Rich in G Unit) (Extracted with Methanol) with Triethylsilane (Et.SUB.3.SiH)

[0207] Lignin from F315 sawdust mixture (sawdust mixture marketed by the company SPPS extracted from species belonging to the family Pinaceae) was extracted with methanol, by the method described by K. Barta, G. R. Warner, E. S. Beach, P. T. Anastas, Green Chem., 2014, 16, pages 191-196.

[0208] The same procedure is used as for depolymerization of lignin from plane. This method leads to complete dissolution of the lignin and its depolymerization, generating a mixture of products.

[0209] Among the most volatile products, IIa and IIb are identified by NMR and GC-MS as indicated in Table 1. Hydrolysis of the mixture leads to products of formula (IV).

Example 12

Depolymerization of Lignin Obtained from F315 Sawdust Mixture (Rich in G Unit) (Extracted with Acetone) with Triethylsilane (Et.SUB.3.SiH)

[0210] Lignin from F315 sawdust mixture (sawdust mixture marketed by the company SPPS extracted from species belonging to the family Pinaceae) was extracted with acetone in the presence of a catalytic amount of hydrochloric acid, by the method described by S. Bauer, H. Sorek, V. D. Mitchell, A. B. Ibez, D. E. Wemmer, J. Agric. Food Chem. 2012, 60, pages 8203-8212.

[0211] The same procedure is used as for depolymerization of lignin from plane. This method leads to complete dissolution of the lignin as well as the production of a mixture of products of general formula II.

[0212] Among the most volatile products, IIb is identified by NMR and GC-MS as indicated in Table 1. Hydrolysis of the mixture leads to products of formula (IV).

Example 13 (Comparative)

Depolymerization with Triethylsilane (Et.SUB.3.SiH) of Commercial Lignin (Aldrich: Kraft Lignin) Obtained from Softwood and Desulfurized Using Soda

[0213] The same procedure as for depolymerization of lignin from eucalyptus (Eucalyptus camaldulensis) is used for depolymerization of lignin from the Kraft process, having a level of sulfur of 3.76 wt % relative to the total weight of lignin. No dissolution or depolymerization was observed for this lignin. When this same sample of lignin is treated by the AVIDEL process again, the level of sulfur reaches 3 wt % relative to the total weight of the lignin, but depolymerization still does not take place. This means that the presence of sulfur in the reaction mixture plays a crucial role in deactivation of the reaction.

[0214] The compounds of formula (IV) obtained after hydrolysis of the silylated compounds resulting from the depolymerization of lignin are of formula (IV)

##STR00009##

[0215] in which [0216] R.sup.8, R.sup.9, R.sup.10 represent, independently of one another, a hydrogen atom, a hydroxyl group; [0217] Y represents an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group CR.sup.4O with R.sup.4 representing a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group, [0218] said alkyl, alkenyl and alkynyl groups optionally being substituted.

[0219] Table 1 summarizes the results of depolymerization of the lignins in the examples given above. [0220] In Table 1: [0221] % of lignin extracted denotes the percentage by weight of lignin extracted relative to the weight of wood used initially; [0222] wt % denotes the percentage by weight of the species relative to the initial weight of lignin introduced evaluated by external calibration of GC-MS by the same molecules under analysis.

[0223] The operating conditions applied for obtaining the results in Table 1 are as follows: Lignin, Et.sub.3SiH (275 to 320 wt %/weight of lignin), B(C.sub.6F.sub.5).sub.3 (15 to 25 wt %/weight of lignin), CH.sub.2Cl.sub.2 (995 wt %/weight of lignin), 25 C., 16 hours.

TABLE-US-00001 Method used for wt % of Source of extracting lignin lignin lignin extracted wt % IIa wt % IIc wt % IIb wt % IId F315 methanol 2 15 1 (softwood) reflux Stone pine AVIDEL 8 16 (softwood) Western red AVIDEL 7 8 2 cedar (hardwood) Common AVIDEL 6 16 18 spruce (softwood) F315 ethanol reflux 3 13 15 (softwood) F315 acetone 2 4 (softwood) reflux Common AVIDEL 14 13 22 beech (hardwood) Lombardy AVIDEL 17 19 21 poplar (hardwood) Silver birch AVIDEL 13 10 26 (hardwood) Holm oak AVIDEL 12 6 37 13 (hardwood) Date palm AVIDEL 10 3 6 10 79 (hardwood) Eucalyptus AVIDEL 9 8 30 17 35 (hardwood) Green plum AVIDEL 18 20 3 26 (hardwood) Plane AVIDEL 10 15.6 9 65 (hardwood) Cedar of AVIDEL 6 14 3 Lebanon (softwood) Nordmann AVIDEL 20 2 fir (softwood) Gaboon AVIDEL 7 6 ebony (hardwood)
Experimental Protocol for Hydrolysis of Silylated Aromatic Compounds Resulting from Reductive Depolymerization of Lignin

[0224] nBu.sub.4NF.3H.sub.2O (315.5 mg, 2.1 mmol, 2.1 equiv) was added slowly (about 5 min), under argon, to a solution of IIa (380.7 mg; 1.0 mmol, 1 equivalent) in 4 mL of THF. The solution was stirred for 1 h at 20 C. Then the volatiles were evaporated under vacuum and 4 mL of dichloromethane was added. Finally, compound IIa was purified on a silica column using gradient elution from 50% dichloromethane to 50% ethyl acetate. Evaporation of the solvents gives 4-propylbenzene-1,2-diol (141.5 mg; 0.9 mmol; 84%) in the form of a colorless oil.

[0225] Table 2 summarizes the results of hydrolysis of the silylated aromatic molecules IIa-IIf resulting from reductive lignin depolymerization of the lignins in the examples given above.

TABLE-US-00002 TABLE 2 Silylated aromatic Amount of Yield molecule TBAF (equiv.) Appearance isolated (%) IIa 2.1 Colorless oil 84 IIb 3.1 Colorless oil 86 IIc 3.1 White powder or 94 colorless crystals IId 4.1 White gum 82 IIe 1.1 Colorless oil 77 IIf 2.1 White powder 92

[0226] After hydrolysis, all the OSi bonds are transformed to OH.