Method for preparing an acetal-protected sugar

Abstract

Method for preparing an acetal-protected sugar involving the step of reacting a diol group of a sugar selected from the group consisting of an aldopentose and an aldohexose with one or two compounds of formula (Ia) and / or (Ib) in the presence of a homogenous or heterogenous catalyst to form an acetal-protected sugar selected from the group consisting of a compound of formula (II), (III) and (IV) wherein R1 and / or R2 are independent from each other -Z-X, and wherein Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 C1- C4-alkyl groups or 1 to 4 halogen atoms, or -B-D, wherein B is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent, D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 C1-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3 groups or 1 to 4 halogen atoms and combinations thereof, and wherein Z may be present or absent, and X is -COOH, –CH(COOH)2, –COOR3, CHO, –C2H3, –C2H, -CHOR4OR5, – N3, –NHR6, -NR7R8, -F, -Cl, -Br, -I, or if Z is present, –OH, NH2, or -SH; R3, R4 and R5 are independently selected from the group consisting of a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C1 to C4 alkyl groups and / or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo; R6 is a C1-C4-alkyl group; R7, R8 and R9 are independently from each other a C1-C4-alkyl group; R30 and R31 are independently selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30 and R31 cannot both be hydrogen; R10 is selected from the group consisting of -H, -OH, - CH2OH, -OR13 or -CH2OR14; R11 and R12 are independently selected from the group consisting of -OH or -OR13; R13 and R14 are independently selected from a hydrocarbon moiety with 1 to 10 carbon atoms; and n and p are independently from each other either 0 or 1.

Description

[0001] Method for preparing an acetal-protected sugar

[0002] The present invention relates to a method for preparing an acetal- protected sugar. Further disclosed is a method for preparing an acetal-protected lignin fragment.

[0003] The use of plastic materials, such as poly(ethylene terephthalate) (PET) or polypropylene (PP), is ubiquitous. However, plastic pollution has become one of the most pressing environmental issues, as rapidly increasing production of disposable plastic products overwhelms the world's ability to deal with them. Therefore, new materials that can potentially replace traditional plastic materials are being researched.

[0004] Lignin is reported to be the second most abundant natural polymer on earth after cellulose, accounting for 15-30 wt.% of lignocellulosic biomass. Unlike cellulose and hemicellulose, the two other major constituents of lignocellulosic biomass, lignin is not a polysaccharide. Instead, lignin is said to contain a significant amount of aromatic subunits. This structure imparts lignin with an energy density that is 30% higher than cellulosic polymers and makes it one of the few natural sources of aromatic molecules. Because of these properties, lignin monomers are increasingly recognized as an essential precursor for many different applications.

[0005] WO2017178513A1 discloses a pretreatment method for lignocellulosic biomass, resulting in high lignin monomer yields. The method involves heating the lignocellulosic composition with an aldehyde, ketone, boronic acid or a compound selected from 2-methoxypropene, dimethyl carbonate, and 2,2-dimethoxypropane under acidic conditions. The preferred protecting agent, formaldehyde, performs well but poses safety issues when upscaling to a large-scale operation. Alternatively, glyoxylic acid (GA) as a safer, possibly biobased, but relatively expensive, viscous and hard-to-recycle alternative aldehyde can be used. Digyloxylic acid xylose (DGAX) and its corresponding esters such as dimethylglyoxylate xylose (DMGX) can be used to produce a new class of polyesters, poly(alkylene xylosediglyoxylates) (PAX), that have similar properties to poly(ethylene terephthalate) (PET) but are bio-based and can also be easily chemically recycled and will eventually degrade back to sugars in the presence of water. Additionally, this diacid / diester could be directly utilized in a wide variety of other applications (e.g. adhesives, surfactant etc.) or could serve as a platform molecule for synthesis of acetal- stabilized xyloses with other functionalities (e.g. dialcohol, diamine, etc.).

[0006] However, currently, DGAX / DMGX is synthesized using a homogenous synthesis method as disclosed in EP 4045514 Al in a highly-viscous reaction mixture and requires a large excess of glyoxylic acid, which is expensive and very difficult to recycle.Also, the corrosive nature and limited stability of glyoxylic acid require careful handling and storage conditions. As a result, the scaling of this process would lead to high operating costs and increased cost of equipment and maintenance. Additionally, compared to formaldehyde, the use of glyoxylic acid significantly increases the viscosity of the reaction mixture and therefore potentially require significant capital expenditure for high-torque reactor systems.

[0007] The problem of the present invention is to provide a method for the preparing of an acetal-protected sugar, which is more environmentally friendly, cost-efficient and easy to scale.

[0008] This problem is solved by the method for the preparing of an acetal- protected sugar according to claim 1. Further preferred embodiments are subject of the dependent claims.

[0009] The invention refers to a method for preparing an acetal-protected sugar involving the step of reacting a diol groups of a sugar selected from the group consisting of an aldopentose and an aldohexose with one or two compounds of formula (la) and / or (lb) in the presence of a homogenous or heterogenous catalyst to form an acetal-protected sugar selected from the group consisting of a compound of formulae (II), (III), and (IV)

[0010] wherein R4and / or R2are independent from each other and are -Z-X, and wherein

[0011] Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 C4- C4-alkyl groups or 1 to 4 halogen atoms, or -B-D, wherein

[0012] B is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent,

[0013] D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 C1-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3groups or 1 to 4 halogen atoms and combinations thereof, and wherein

[0014] Z may be present or absent, and

[0015] X is -COOH, -CH(COOH)2, -COOR3, CHO, -C2H3, -C2H, -CHOR4OR5, - N3, -NHR6, -NR7R8, -F, -Cl, -Br, -I, or if Z is present, -OH, NH2, or -SH;

[0016] R3, R4and R5are independently selected from each other and are a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C4to C4alkyl groups and / or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo;

[0017] R6is a C4-C4-alkyl group;

[0018] R7and R8are independently selected from each other and are a C4-C4-alkyl group; R30and R31are independently from each other selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30and R31cannot both be hydrogen;

[0019] R10is selected from the group consisting of -H, -OH, -CH2OH, - OR13or -CH2OR14;

[0020] Rn and R42are independently selected from the group consisting of -OH or -OR15;

[0021] R13JR14and R15are independently selected from a hydrocarbon moiety with 1 to 10 carbon atoms; and n and p are independently from each other either 0 or 1.

[0022] For chemical moieties, such as alkyl moieties or aromatic or aliphatic moieties, which are substituted, one of the hydrogen atoms in the moiety is replaced by the substituent. For example, a -C6H5- moiety that is substituted with a methyl group, corresponds to a -C6H4(CH3)-moiety.

[0023] The term "linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C4to C4alkyl groups and / or 1 to 4 halogen atoms" refers to a linear or branched or cyclic hydrocarbon chain containing 1 to 20 of carbon atoms. Examples of said term as used herein include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, fluoromethyl, difluoromethyl, trifluoromethyl, fluoroethyl, difluoroethyl, 1-fluoroisopropyl, 1,1- difluoroisopropyl, 1,1,1- trifluoroisopropyl, 1,1,1,2-tetrafluoro-isopropyl, pentafluoroisopropyl, hexafluoroisopropyl, hexyl and the like.

[0024] The term "aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 C4to C4alkyl groups and / or 1 to 4 halogen atoms" describes an aromatic ring structure containing 6 carbon atoms. Examples of said term as used herein include phenyl, benzyl

[0025] (wherein B is CH2) and tolyl.

[0026] The method for the preparing of an acetal-protected sugar according to the invention has the advantage, that the acetal compound of formula (la) and / or (lb), are used as a protecting agent to obtain the acetal-protected sugar. By using the acetal as reagent and in excess the viscosity of the acetal-protected sugar is reduced. By reducing the viscosity, the scalability of the production method is improved which significantly reduces the capital costs.

[0027] Another advantage of the inventive method is that through using of acetal as reagents, common reactivity towards undesired side reactions of aldehydes and ketones (e.g. aldo condensation), are significantly reduced.

[0028] Additionally, the production method according to the invention is not restricted to a specific sort of catalyst, since the reaction can be catalyzed by a homogeneous or heterogeneous catalysis.

[0029] Furthermore, by utilizing an esterified form of glyoxylic acid (here compound (la) and / or (lb)) it is possible to produce digyloxylic acid xylose esters in one step from D-xylose rather than two steps as disclosed in WO 2021074211 Al. This reduces the costs compared to the synthesis in the prior art. Yet another advantage of the production method according to the invention is that the prepared tricyclic compounds are very stable and can be easily isolated and purified. Furthermore, said tricyclic compounds can be used as building blocks for polymers having higher glass transition temperatures as compared to most other monomers mentioned in the prior art. For example, polyesters produced from DMGX and 1,2-ethanediol have glass transition temperatures of 137°C whereas polymers from the same diol and commercial terephthalic acid have glass transitions of only 60-75°C.

[0030] The replacement of formaldehyde as a protective agent with glyoxylic acid increases the production costs, the viscosity of the product and decreases the rate of recyclability. On the other hand, the usage of an acetal form of glyoxylate, such as ethyl diethoxy acetate (EDEA), lowers the viscosity of the reaction product. Additionally, by using acetalized forms of glyoxylic acid such as EDEA the advantages are that the protective agent can generally be purchased in pure forms rather than as monohydrates or aqueous solutions, as is the case for glyoxylic acid. This circumvents the need for expensive drying steps. Second the reaction by-product, for example in DGAX synthesis, becomes an alcohol such as methanol or ethanol, which is far easier to remove from the reaction mixture than water.

[0031] Preferably the method for preparing an acetal-protected sugar involves a step of heating the mixture of a diol group of a sugar in the presence of a homogenous or heterogenous catalyst to a temperature between 50°C and 150°C, more preferably to a temperature between 70°C and 110°C and most preferably to a temperature between 80°C and 100°C.

[0032] In a preferred embodiment of the method for preparing an acetal- protected sugar the heating of the mixture of a diol group of a sugar in the presence of a homogenous or heterogenous catalyst occurs under reduced pressure between 20 mbar and 450 mbar, more preferably between 50 mbar and 100 mbar. Preferably the method for preparing an acetal-protected sugar involves a step of heating the mixture of a diol group of a sugar in the presence of a homogenous or heterogenous catalyst under reduced pressure for 1 to 10 hours, more preferably for 3 to 8 hours.

[0033] In a preferred embodiment of the method for preparing an acetal- protected sugar -Z-X is selected from the group consisting of - Ph-COOH, -CH2-Ph-COOH, -CH2-CH2-Ph-COOH, -CH2-CH2-CH2-Ph-COOH, -CH=CH-CH2-Ph-COOH, -CH2- CH=CH-Ph-COOH - -CH(COOH)2, -COOMe, -CH2COOMe, -CH2-CH2-COOMe, -Ph-COOMe, -CH (COOMe)2, -C6H10-COOMe, -COOEt, -CH2COOEt, -CH2CH2COOEt, -Ph-COOEt, -CH(COOEt)2, -C6H10-COOEt, -CH2-CH2-CHO, -CH2-CH2-CH2-CHO, -CH=CH-CH2-CHO, -CH2-CH=CH-CHO, -Ph-CHO, -C6H10-CHO, -CHCH2, -CH2CHCH2, -CH2CH2CHCH2, -Ph-CHCH2, -C6H10CHCH2, -CH2CCH, -CH2CH2CCH, -Ph-CCH, -C6HIQ-CCH, -CH2N3, -CH2CH2N3, -Ph-N3, -C6H10-N3, -CH2NH2, -CH2CH2NH2, -Ph-NH2, -C6H10-NH2, -CH2SH, -CH2CH2SH, -Ph-SH, -C6H10-SH, -NH-CH3, -CH2-NH-CH3, -CH2CH2-NH-CH3, -Ph-NH-CH3, -C6H10-NH-CH3, -CH2OH, -CH2CH2OH, -Ph-OH, -C6H10-OH, -CH2F, -CH2CH2F, -CH2CH2CH2F, -Ph-F, -C6H10F, -CH2C1, -CH2CH2C1, -CH2CH2CH2C1, -Ph-Cl, -C6H1O-C1, -CH2Br, -CH2CH2Br, -CH2CH2CH2Br, -Ph-Br, -C6H10-Br and -CH2I, -CH2CH2I, -CH2CH2CH2I, -Ph-I, -C6HIQ-I, whereby Me stands for methyl, Et stands for ethyl and Ph stands for a phenyl ring.

[0034] One embodiment of the present invention relates to a method, wherein R2and / or R2are independent from each other -Z-X, and wherein

[0035] Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 Ch-C^alkyl groups or 1 to 4 halogen atoms, or -B-D, wherein

[0036] B is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent,

[0037] D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 Ci-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3groups or 1 to 4 halogen atoms and combinations thereof, and wherein

[0038] Z may be present or absent, and

[0039] X is -CH(COOH)2, -COOR3, CHO, -C2H3, -C2H, -CHOR4OR5, -N3, -NHR6, - NR7R8, -F, -Cl, -Br, -I, or if Z is present, -COOH, -OH, NH2, or - SH; and preferably if Z is a linear, branched or cyclic hydrocarbon moiety X is not -COOH.

[0040] In a preferred embodiment of the method for preparing an acetal- protected sugar the reaction is carried out under neat conditions. The term "neat conditions" refers to a reaction mixture wherein aside from the starting material no additional solvent is used. Within the context of the present invention a solvent is a substance that has the ability to dissolve the starting material to form a homogeneous mixture. The reaction under neat conditions has the advantage that no solvent has to be removed from the product of the reaction and that there are no cross reactions of the starting material with the solvent to form an unwanted byproduct. Furthermore, as there is no solvent, the recycling of the solvent no longer needs to be considered which results in an eco-friendlier production of acetal-protected sugars. Lastly, the ability to perform the reaction in neat conditions leads to high product concentrations in the effluent stream, greatly reducing process volumes and increasing overall productivity.

[0041] In a another embodiment of the method for preparing an acetal- protected sugar, the reaction is carried in a solvent, more preferably in a solvent selected from the group consisting of dimethylisosorbide, cyclic ethers, in particular 1,4-dioxane or 2- methyltetrahydrofuran, sulfolane, sulfolene, aliphatic acids in particular acetic acid, alkylpyrrolidone, cyclic carbonates, cyclic esters, in particular y-valerolactone or y-gamma butyrolactone, acetonitrile and non-cyclic ethers, in particular diethyl ether, mono ethylene, diethylen, triethylene, triethylene glycol mono / di ethers. These solvents have the advantage that they can be easily removed, while at the same time allow high conversion rate of the sugar to be protected.

[0042] In a preferred embodiment of the method for preparing an acetal- protected sugar the unreacted compound of formula (la) and / or (lb) can be recovered to reduce the production cost.

[0043] In a further preferred embodiment of the method for preparing an acetal-protected sugar the unreacted compound of formula (la) and / or (lb) is recycled by means of distillation. The recovery of unreacted compounds of formula (la) and / or (lb) by distillation has the advantage that unreacted compounds of formula (la) and / or (lb) can be recycled and reused in a later process with a mild isolation process, that does not interfere with the chemical structure of compounds of formula (la) and / or (lb).

[0044] In a preferred embodiment of the method for preparing an acetal- protected sugar, Z in Eh and / or R2of compound (la) and (lb) is absent. The term "absent" in the context of this invention refers to a compound (la) and (lb), wherein the in residual groups Eh and / or R2X is directly attached to carbon atom of the R31-O-CEE-O-R30backbone. In this particular embodiment the compound (la) and (lb) has a formula of When Z is absent, the proximity of the functional group to the electrophilic acetal can lead to an increase in reactivity of the attached functional group during subsequent polymerization. For example, when X is COOR3in (Ia) / (Ib), the electron withdrawing effect of the acetal increases electrophilicity of the carbonyl making it more prone to nucleophilic attack. Additionally, this enables production of bifunctional molecules from renewable sugars with minimal incorporation of fossil-based carbon, if (la) and (lb) are fossil-derived.

[0045] In a preferred embodiment of the method for preparing an acetal- protected sugar R30and R31are the same. The usage of acetal compounds according to formula (la) and / or (lb) wherein R30and R31are the same have the advantage that these acetal compounds are more practical to synthesize and produce significantly less by-products in the production reaction to form acetal-protected sugar. The reagents wherein R30and R32are the same are far easier to produce than those, where R30and R31are different. This will likely lead to a more economical process.

[0046] In a preferred embodiment of the method for preparing an acetal- protected sugar in R2and / or R2Z is -CH2or absent and X is a halogen selected from the group consisting of Cl and Br or -COOR3and R3is -CH3or -CH2CH3. More preferably, R2and / or R2are selected from a group consisting of -CH2-COOCH3, -CH2-COOCH2CH3, -COOCH3, CH2C1, CH2Br and -COOCH2CH3.

[0047] In a preferred embodiment of the method for preparing an acetal- protected sugar R30, R31and R3are the same. More preferably, the compound (la) and / or (lb) are selected from the group consisting of:

[0048]

[0049] Further good results could be obtained with the following halogenated acetals:

[0050] As described above the replacement of formaldehyde as a protective agent with glyoxylic acid increases the costs, viscosity and is hard to recycle. The usage of an acetal form of glyoxylate, called ethyl diethoxy acetate (EDEA), lowers the viscosity of the reaction product. Additionally, by using acetalized forms of glyoxylic acid such as EDEA the advantages are that the protective agent can generally be purchased in pure forms rather than as monohydrates or aqueous solutions, as is the case for glyoxylic acid. This circumvents the need for expensive drying steps. Second the reaction by-product, for example in DGAX synthesis, becomes an alcohol such as methanol or ethanol, which is far easier to remove from the reaction mixture than water. The presence of the linking group -Z leads to polymer precursors with enhanced flexibility due the extra carbon spacer between the acetal and functional group.

[0051] In a preferred embodiment of method for preparing an acetal- protected sugar compound (la) and / or (lb) are selected from the group consisting of

[0052] These molecules are all attainable at industrial scale and are prime candidates for production of DGAX esters, or slightly modified DGAX esters (with one extra carbon for increased flexibility. Said molecule can be used in the production of performance polymers.

[0053] A more preferred embodiment of the invention relates to a method for preparing compound (II)

[0054] wherein Ri0, Rn and n are defined as above and Ri and R2are selected from the group consisting of -COOR3, -CH2COOR3and -CH2OH, wherein R3is defined as above. It has surprisingly been shown that compound (II), wherein R2and R2are -COOR3and R3is a methyl group, has imparting performance properties when incorporated into polyesters. This compound was polymerized with a range of diols to produce a family of polyesters, hereafter referred to as poly(alkylene xylosediglyoxylates) (PAX). These polyesters exhibited strong, stiff and ductile mechanical properties with high glass transition temperatures and good gas barrier properties making them a potential replacement for poly(ethylene terephthalate) (PET). Notably, they were chemically recyclable in remarkably mild conditions and are degradable in water at room temperature.

[0055] Additionally, it has surprisingly been shown that an acetal- protected sugar of compound (II), wherein R2and R2are -CH2COOR3, has an enhanced flexibility due to the extra carbons over a compound (II), wherein R2and R2is -COOR3.

[0056] A preferred embodiment of the invention relates to a method for preparing compound (III) or (IV)

[0057] wherein Eh, R2, Rio, Rn, R22, n, and p are defined as above.

[0058] A more preferred embodiment of the invention relates to a method for preparing compound (III) or (IV) wherein R10, Rn, R12, n and p are defined as above and Ro and R2are selected from the group consisting of -COOR3, -CEE2COOR3and -CEE2OEE, wherein R3is defined as above. It has surprisingly been shown that an acetal-protected sugar of compound (III) or compound (IV), wherein R2and R2are selected from the group consisting of -COOR3and -CEE2OEE leads to excellent properties of the resulting polymers, as described also for compound (II) above. EEence such a compound (III) or compound (IV) is preferably used in the production of high- performing materials, which require for example mechanical resistance, thermal stability or the ability to be used as a gas barrier. Additionally, it has surprisingly been shown that an acetal-protected sugar of compound (III) or compound (IV), wherein R4and R2are -CH2COOR3, has an enhanced flexibility due to the extra carbons over a compound (II), wherein R4and R2is -COOR3.

[0059] In a preferred embodiment of method for preparing an acetal- protected sugar the catalyst is a homogenous catalyst. More preferably the homogenous catalyst is an organic or an inorganic acid and most preferably selected from the group consisting of H2SO4, H3PO4, HBr, HC1, FeCl3, A1C13, TiCl4, RUC13, SnCl4, phosphotungstic acid, phosphomolybdic acid, tungstosilicic acid, methano sulfonic acid and para-toluene sulfonic acid. These catalysts are available at industrial scale at reasonably low cost. Additionally, the handling of the majority of these molecules at large scale is well established.

[0060] In a preferred embodiment of method for preparing an acetal- protected sugar the catalyst is a heterogeneous catalyst. Preferably the heterogeneous catalyst is a heterogeneous acidic catalyst, more preferably the heterogeneous catalyst is a Bronsted acidic catalyst and most preferably the heterogeneous catalyst is selected from the group consisting of acidic zeolite, acidic doped zeolite, acid site- functionalized resin, acid site-functionalized oxide, acidic oxide, and an immobilized versions of the homogeneous acids selected from the group consisting of H2SO4, H3PO4, phosphotungstic acid, phosphomolybdic acid, tungstosilic acid, methano sulfonic acid, silica sulfuric acid and para-toluene sulfonic acid.

[0061] The term "acid site-functionalized resin" as used herein refers to a resin or polymer that acts as a medium for ion exchange, synthesized from an organic polymer substrate. The organic polymer substrate is for example a sulfonated polystyrene divinylbenzene or a sulfonated tetrafluoroethylene- based fluoropolymer-copolymer, resulting in a strongly acidic cation exchange resin or polymer. Non- limiting examples include Amberlyst-15, Amberlyst-36, Amberlite (e.g., Amberlite IRC120), Dowex D 2030, Nafion NR50 and Nafion SAC13.

[0062] The term "acid site-functionalized oxide" means an oxide such as zirconia, alumina or silica that is that is functionalized to yield e.g. a sulphated or sulphonated material. Such solid acidic metal oxides may optionally be supported onto a carrier material.

[0063] The term "acidic oxide" means metal oxides that have a Bronsted acidity such as niobia, or alumina.

[0064] The term "zeolite" as used herein refers to both natural and synthetic microporous crystalline silicate materials (including aluminosilicates, borosilicates and aluminoborosilicates) having a definite crystalline structure as determined by X-ray diffraction. A zeolite comprises a system of channels which may be interconnected with other channel systems or cavities such as side-pockets or cages. The channel systems may be three-dimensional, two- dimensional or one-dimensional.A zeolite comprises SiO4and X04tetrahedra, wherein X can be Al (aluminum) or B (boron). A zeolite may comprise a combination of A104and B04tetrahedra. In one embodiment, X is Al, and the zeolite comprises no B04tetrahedra. The SiO4and X04tetrahedra are linked at their corners via a common oxygen atom. The Atlas of Zeolite Framework Types (C Baerlocher, LB McCusker, DH Olson, 6th ed. Elsevier, Amsterdam, 2007) in conjunction with the web-based version (http: / / www.iza-structure.org / databases / ") is a compendium of topological and structural details about zeolite frameworks, including the types of ring structures present in the zeolite and the dimensions of the channels defined by each ring type. Proven recipes and good laboratory practice for the synthesis of zeolites can be found in the "Verified synthesis of zeolitic materials" 2nd Edition 2001. Various proven recipes for the synthesis comprising BO tetrahedra are available. For example, the synthesis and characterization of boron-based zeolites having a MFI topology has been described by Cichocki and Parasiewicz-Kaczmarska (Zeolites 1990, 10, 577-582).

[0065] Suitable zeolites for use in the process according to the present invention can comprise: at least two, preferably two or three, non-interconnected and parallel channel systems wherein, at least one of said channel systems comprises 8- or more-membered ring channels; and a framework Si / X2 ratio of at least 4 as measured by NMR; or at least two, preferably two or three, interconnected and non- parallel channel systems wherein, at least one of said channel systems comprises 10- or more-membered ring channels; and a framework Si / X2 ratio of at least 4 as measured by NMR; or three interconnected and non-parallel channel systems wherein at least two of the channel systems comprise 10-or more- membered ring channels, and a framework Si / X2 ratio of at least 4 as measured by NMR. wherein each X is Al or B.

[0066] As used herein, the term "channel system" refers to a system of parallel or non-parallel and crystallographically equivalent channels, wherein the channels are 8-membered ring channels or larger, for example wherein the channels are 10-membered ring channels or 12-membered ring channels. Accordingly, as used herein, the term "channel" refers to an 8-or more membered ring channel which is part of a system of parallel or non-parallel and crystallographically equivalent channels.

[0067] Suitable zeolites for use in the present process comprise 10-or more-membered ring channels, such as 12-membered ring channels (12MR), or larger. The ring size for each known zeolite framework type is provided in the Atlas of Zeolite Framework Types (C Baerlocher, LB McCusker, DH Olson, 6th ed. Elsevier, Amsterdam, 2007), which is incorporated herein by reference.

[0068] As used herein the terms "8-membered ring channels" or "8MR" refer to a channel comprising unobstructed 8-membered rings, wherein the 8-membered rings define the smallest diameter of the channel. An 8- membered ring comprises 8 T atoms, and 8 alternating oxygen atoms (forming the ring), wherein each T is Si, Al or B. As used herein the terms "10-membered ring channels" or "10MR" refers to a channel comprising unobstructed 10-membered rings, wherein the 10-membered rings define the smallest diameter of the channel. A 10-membered ring comprises 10 T atoms, and 10 alternating oxygen atoms (forming the ring), wherein each T is Si, Al or B. As used herein the terms "12-membered ring channels" or "12MR" refers to a channel comprising unobstructed 12-membered rings, wherein the 12-membered rings define the smallest diameter of the channel. A 12-membered ring comprises 12 T atoms, and 12 alternating oxygen atoms (forming the ring), wherein each T is Si, Al or B. As used herein, the term "10-or-more- membered ring channel" refers to a 10-membered ring channel or larger, and therefore comprises for example both 10-membered ring channels and 12-membered ring channels.

[0069] The framework Si / X2 ratio may be determined via Nuclear Magnetic Resonance (NMR) measurements, more particularly 29Si and 27A1 NMR. In a preferred embodiment, there is no framework B, and the Si / X2 ratio is equal to the Si / A ratio. The determination of the Si / A ratio by NMR may be performed as described by Klinowski (Ann. Rev. Mater. Sci. 1988, 18, 189-218); or as described by G. Engelhardt and D. Michel (High-Resolution Solid-State NMR of Silicates and Zeolites. John Wiley & Sons, Chichester 1987. xiv, 485 pp). The determination of the Si / B2 ratio by NMR may be performed as discussed by D. Trong On et al. (Studies in Surface Science and Catalysis 1995, 97, 535-541; Journal of Catalysis, November 1995, Volume 157, Issue 1, Pages 235-243).

[0070] Zeolites are thermostable catalysts and can therefore be regenerated by calcrnatron, in contrast wrth classic thermolabrle ron-exchange resins such as Amberlyst-15.

[0071] The presence of a heterogeneous catalyst has the advantages that a high separability of the products is provided, while the catalyst has a high rate of recyclability and is easy to adjust to specific conditions (tunability).

[0072] Further disclosed is a method for preparing an acetal-protected lignin fragment involving the step of reacting a diol group of a lignocellulose-containing material with one or two compounds of formula (la) and / or (lb)

[0073] (la) (lb) in the presence of a homogenous or heterogenous catalyst to form an acetal protected fragment of lignin having one or more functional groups -Z-X wherein

[0074] Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, or an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 Ci-C4-alkyl groups or 1 to 4 halogen atoms, and may be present or absent;

[0075] X is -CH(COOH)2, -COOR3, -C2H3, -C2H, -CHOR5OR6, -N3,-NHR7, -NR8R9, -F, -Cl, -Br or -I, or if Z is present, -OH, NH2, or -SH;

[0076] R3, R4and R5are independently selected from each other and are a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 Ci to C4alkyl groups and / or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo;

[0077] R6is a C1-C4-alkyl group;

[0078] R7,R8and Rgare independently selected from each other and are a C4-C4-alkyl group;

[0079] R30and R3I are independently from each other selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30and R31cannot both be hydrogen.

[0080] The preferred embodiments described in connection with the method for preparing an acetal-protected sugar are also applicable to the disclosed method for preparing an acetal-protected lignin fragment. Specifically, the preferred embodiments discussed in relation to the "method for preparing an acetal-protected sugar" are equally applicable to the "method for preparing an acetal-protected lignin fragment". The (preferred) definitions for groups within formulae (Ta) and (lb), given above in connection with the acetal-protected sugars are similarly applicable to the acetal-protected lignin fragments, except where a different definition has been specifically indicated.

[0081] The hereby disclosed method for the preparing of an acetal-protected lignin fragment has the advantage, that the acetal compound of formula (Ta) and / or (lb),

[0082] are used as a protecting agent to obtain an acetal-protected lignin fragment. By using the acetal as reagent and in excess the viscosity of an acetal-protected lignin fragment is reduced. By reducing the viscosity, the scalability of the production method is improved which significantly reduces the capital costs.

[0083] Another advantage of the inventive method is that through using of acetal as reagents, common reactivity towards undesired side reactions of aldehydes and ketones (e.g. aldo condensation), are significantly reduced.

[0084] Additionally, the production method disclosed herein is not restricted to a specific sort of catalyst, since the reaction can be catalyzed by a homogeneous or heterogeneous catalysis. On one hand, the Lewis acid is effective, cost-efficient, and shortens the reaction time. On the other hand, a heterogeneous catalyst also performs well and simplifies the work-up process, as it can be filtered and recycled.

[0085] A preferred embodiment of the present disclosure relates to a method for preparing acetal protected fragment of lignin having one or more functional groups -Z-X.

[0086] The following reaction scheme discloses the preparation of an acetal-protected lignin fragment, wherein Y is H or OMe.

[0087]

[0088] A preferred embodiment of the present disclosure concerns a method for preparing acetal protected fragment of lignin having one or more functional groups -Z-COOR3, with Z and R3being defined as above.

[0089] The following reaction scheme discloses the preparation acetal- protected lignin fragment with one functional group (here -COOR3), wherein Y is H or OMe and R3is defined as above. A more preferred embodiment of the present disclosure relates to a method for preparing acetal protected fragment of lignin having one or more functional groups -Z-COOR3, wherein Z is absent. An acetal-protected lignin enables the attachment of a functional group (here -Z-X) to the lignin backbone to expands its potential use in various applications including its use as a surfactant or its use in thermoset resins. The following reaction scheme shows the preparation of an acetal- protected lignin fragment with two functional groups (here -Z-X).

[0090] Figures Figure 1 shows a viscosity measurement of DGAX and DEGX synthesis as a function of time at 90°C.

[0091] Fig. 1 shows the change in viscosity of the reaction mixture over time during the synthesis of digyloxylic acid xylose (DGAX) and dimethylglyoxylate xylose (DEGX). DGAX synthesis was performed in line with the synthesis described in EP4045514A1, using 4 equiv. of glyoxylic acid and 0.2 equiv. of sulfuric acid.

[0092] DEGX was synthesized in line with Example 5 described further below in the experimental section, using 4 equiv. of EDEA, 0.5 g of amberlystl5 per gram of xylose.

[0093] As can be seen from the graph, the viscosity of the reaction mixture during the synthesis of DGAX using glyoxylic acid is highly variable and reaches very high values towards the end. In contrast thereto, during the synthesis of DEGX using ethyl diethoxy acetate (EDEA), the viscosity of the reaction mixture remains low over the entire reaction time. This clearly shows that the usage of an acetal form of glyoxylate, such as ethyl diethoxy acetate (EDEA), lowers the viscosity of the reaction product in comparison to the usage of glyoxylic acid.

[0094] Experimental data

[0095] Example 1

[0096] D-xylose (3.0 g, 33 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (14.1 g, 4 equiv.) and sulfuric acid (32.3 mg, 0.2 equiv.) were added in a 100 mL round bottom flask. The mixture was heated to 90°C under reduced pressure (50 mbar) for 3h with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), the yield was followed by GC-FID. After the trans-acetalization, the yield was 64%.

[0097] Example 2

[0098] D-xylose (3.0 g, 33 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (21.0 g, 6 equiv.) and phosphomolybdic acid (0.75g, 6.2mol% H+) were added in a 50 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 5h with a stirr bar (500rpm).

[0099] The resulted solution was cooled to room temperature (~23-25°C), the yield was followed by GC-FID. After the trans-acetalization, the yield was 89%. Example 3

[0100] D-xylose (3.0 g, 33 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (14.1 g, 4 equiv.) and tungstosilic acid (2.25g) were added in a 50 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 5h with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC-FID. After the trans-acetalization. From this reaction, further experiments were conducted to extract the catalyst by liquid-liquid extraction, then from theoretically non-consumed EDEA equivalents, 74% of EDEA was recovered by distillation with a purity >95% from quantitative NMR and the reaction resulted in DEGX isolated yields of 33%.

[0101] Example 4

[0102] D-xylose (3.0 g, 33 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (14.1 g, 4 equiv.) and sulphated silica (2.25 g) were added in a 100 mL round bottom flask. The mixture was heated to 90°C under reduced pressure (50 mbar) for 6h with a stirr bar (500 rpm). The resulted solution was cooled to room temperature (~23-25°C). The yield was followed by GC-FID. After the trans-acetalization, the yield was 55%.

[0103] Example 5

[0104] D-xylose (1.9 g, 13 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (13.6 g, 80 mmol, 6 equiv.) and Amberlyst-15 (0.94 g) were added in a 50 mL round bottom flask. The mixture was heated to 90°C under reduced pressure (50 mbar) for 7h with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC-FID and reached 80%. After the trans- acetalization. From this reaction, further experiments were conducted to extract the catalyst by liquid-liquid extraction, then from theoretically non-consumed EDEA equivalents, 56% of EDEA was recovered by distillation with a purity >95% from quantitative NMR and the reaction resulted in DEGX isolated yields of 50%.

[0105] Example 6

[0106] D-xylose (1.3 g, 8.5 mmol, 1.0 equiv.), recycled ethyl diethoxyacetate - recycled-EDEA (8.7 g, 50 mmol, 6 equiv.) and Amberlyst-15 (0.67 g) were added in a 100 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 3h30 with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC-FID. After the trans-acetalization, the yield was 84%.

[0107] Example 7

[0108] D-xylose (1.9 g, 13 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (13.6 g, 80 mmol, 6 equiv.) and Iron(III) chloride (0.82g, 5.2 mmol, 0.4 equiv) were added in a 100 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 2h30 with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC-FID. After the trans-acetalization, the yield was 81%.

[0109] Example 8

[0110] D-xylose (1.9 g, 13 mmol, 1.0 equiv.), ethyl diethoxyacetate - EDEA (7.0 g, 40 mmol, 3 equiv.), gamma-Valerolactone - GVL (3.9 g, 40 mmol, 3 equiv.) and Iron(III) chloride (0.84g, 5.2 mmol, 0.4 equiv) were added in a 100 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 3h30 with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23- 25°C), The yield was followed by GC-FID. After the trans- acetalization, the yield was 78%.

[0111] Example 9

[0112] D-xylose (1.9 g, 13 mmol, 1.0 equiv.), methyl dimethoxyacetate -

[0113] MDMA (10.4 g, 78 mmol, 6 equiv.) and Iron(III) chloride (1.05g, 6.5 mmol, 0.5 equiv) were added in a 100 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 5h with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC-FID. After the trans-acetalization, the yield was 41%.

[0114] Example 10

[0115] D-xylose (1.9 g, 13 mmol, 1.0 equiv.), methyl dimethoxyacetate - MDMA (5.1 g, 38 mmol, 3 equiv.), gamma-Valerolactone - GVL (4 g, 40 mmol, 3 equiv.) and Iron(III) chloride (0.84g, 5.2 mmol, 0.4 equiv) were added in a 100 mL round bottom flask. The mixture was heated to 90 °C under reduced pressure (50 mbar) for 2h30 with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23- 25°C), The yield was followed by GC-FID. After the trans- acetalization, the yield was 40%.

[0116] Example 11

[0117] Glyoxylic acid 50% wt. solution in water was charged in a round bottom flask and dried under reduced pressure. Ethanol was added and the mixture was heated at 85°C for 4h. The resulted solution was fractionated distilled to obtain a mixture of ethyl glyoxylate, ethyl diethoxyacetate and ethyl ethoxyhydroxyacetate.

[0118] D-Xylose (16.87 g, 112 mmol, 1.0 equiv.), ethyl glyoxylate, ethyl diethoxyacetate, ethyl ethoxyhydroxyacetate mixture (59.22g, 4.7 g, 0.2 equiv.) and silica sulfuric acid were added in a 100 mL round bottom flask. The mixture was heated to 90°C under reduced pressure (100 mbar) for 8h. The resulting solution was cooled to room temperature (~23-25°C) and the catalyst was filtered, washed with ethanol and dried at 80°C to recovery 88% wt. of silica sulfuric acid as a white powder. Glyoxylate mixture (27.53 g) was recovered by distillation and the reaction resulted in DEGX isolated yield of 23%. Example 12

[0119] D-xylose (1.0 g, 1.0 equiv.), Chloroacetaldehyde dimethyl acetal (CADMA)(4.0 equiv.), Gamma-valerolacton (10 mL) and heteropolyacid (phosphotungstic acid, 2.0 molt) were added in a 50 mL round bottom flask. The mixture was heated to 50 °C under reduced pressure (500 mbar) for 5h with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC- FID. After the trans-acetalization, the yield was 19%.

[0120] Example 13

[0121] D-xylose (1.0 g, 1.0 equiv.), Bromooacetaldehyde dimethyl acetal (BADMA)(4.0 equiv.) ,Gamma-valerolacton (10 mL) and heteropolyacid (silicotungstic acid, 0.1 g) were added in a 50 mL round bottom flask. The mixture was heated to 75°C under reduced pressure (300 mbar) for Ih with a stirr bar (500rpm). The resulted solution was cooled to room temperature (~23-25°C), The yield was followed by GC- FID. After the trans-acetalization, the yield was 24%.

[0122] Example 14

[0123] D-xylose (300 mg, 2 mmoles, 1.0 equiv.), FeBr3 (11.8 mg, 40 pmol,4 mol%), 1,4-dioxane (5 mL), and acrolein dimethyl acetal (817 mg, 8 mmoles, 4 equiv.) were added in a 10 mL round bottom flask, which was sealed with a septum. The reaction was stirred at 70°C for 6 hours. After cooling down to room temperature, the mixture was filtered through a short pad of silica gel. Further purification with flash column chromatography (SiO2; ethyl acetate:hexane = 1:1) afforded 159 mg divinyl-xylose (DVX) as colorless oil (35% isolated yield).

[0124] Example 15 as part of the disclosure

[0125] 4.5 grams of the extracted and dried biomass (birch wood) was weighted and transferred into a 100-mL round-bottom flask, which contained an oval PTFE-coated stir bar. Into the flask, 4.8 mL of Chloroacetaldehyde dimethyl acetal (CADMA), 25 mL of 1,4-dioxane, and 0.85 mL of 37% (wt / wt) hydrochloric acid were sequentially added. A condenser was then attached to the flask, connected to a source of cooling water, and a gas bubbler was fitted at the top of the reflux condenser to create an air lock. The mixture was heated to 80 degrees Celsius with stirring for 3 hours and thereafter allowed to cool to room temperature. The cellulose was filtered and washed with dioxane and methanol. 1,4-Dioxane and CADMA were removed by distillation and lignin was solubilized in 1,4-dioxane and precipitated in hexane. Afterwards, a hydrogenolysis was performed on the precipitated lignin (lOOmg) at 250°C with Ru / C (5 wt%, lOOmg) during 3h in dioxane (20mL) under H2pressure (50bar). Monomer yield after the hydrogenolysis is 4.41 wt% biomass (by GC-FID) and the lignin extraction yield is 13.2 wt% biomass.

[0126] Example 16 as part of the disclosure

[0127] 3.5 grams of the extracted and dried biomass (birch wood) was weighted and transferred into a 100-mL round-bottom flask, which contained an oval PTFE-coated stir bar. Into the flask, 25 mL of ethyl diethoxyacetate - EDEA, and 0.54 mL of 98% (wt / wt) sulfuric acid were sequentially added. A condenser was then attached to the flask, connected to a source of cooling water, and a gas bubbler was fitted at the top of the reflux condenser to create an air lock. The mixture was heated to 85 degrees Celsius with stirring for 3 hours and thereafter allowed to cool to room temperature. The cellulose was filtered and washed with dioxane and methanol. 1,4- Dioxane and EDEA were removed by distillation and lignin was solubilized in ethyl acetate and precipitated in diethyl ether. Afterwards, a hydrogenolysis was performed on the precipitated lignin (100 mg) at 250°C with Ru / C (5 wt%, 100 mg) during 3h in dioxane (20 mL) under H2pressure (50 bar). Monomer yield after the hydrogenolysis is 0.3 wt% biomass (by GC-FID) and the lignin extraction yield is 5.9 wt% biomass. Example 17 as part of the disclosure

[0128] 3.5 grams of the extracted and dried biomass (birch wood) was weighted and transferred into a 100-mL round-bottom flask, which contained an oval PTFE-coated stir bar. Into the flask, 25 mL of ethyl diethoxyacetate - EDEA, and 0.79g of 37% (wt / wt) hydrochloric acid were sequentially added. A condenser was then attached to the flask, connected to a source of cooling water, and a gas bubbler was fitted at the top of the reflux condenser to create an air lock. The mixture was heated to 80 degrees Celsius with stirring for 3 hours and thereafter allowed to cool to room temperature. The cellulose was filtered and washed with dioxane and methanol. 1,4- Dioxane and CADMA were removed by distillation and lignin was solubilized in 1,4-dioxane and precipitated hexane. Afterwards, a hydrogenolysis was performed on the precipitated lignin (100 mg) at 250°C with Ru / C (5 wt%, lOOmg) during 3h in dioxane (20 mL) under H2pressure (50bar). Monomer yield after the hydrogenolysis is 1.2 wt% biomass (by GC-FID) and the lignin extraction yield is 6.1 wt% biomass.

[0129] Clauses:

[0130] Clause 1: Method for preparing an acetal-protected sugar involving the step of reacting a diol group of a lignocellulose-containing material with one or two compounds of formula (la) and / or (lb)

[0131] (la) (lb) in the presence of a homogenous or heterogenous catalyst to form an acetal protected fragment of lignin having one or more functional groups -Z-X wherein

[0132] Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 C4- C4-alkyl groups or 1 to 4 halogen atoms, or -B-D, wherein

[0133] B is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent,

[0134] D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 C1-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3groups or 1 to 4 halogen atoms and combinations thereof, and wherein

[0135] Z may be present or absent, and

[0136] X is -COOH, -CH(COOH)2, -COOR3, CHO, -C2H3, -C2H, -CHOR4OR5, - N3, -NHR6, -NR7R8, -F, -Cl, -Br, -I, or if Z is present, -OH, NH2, or -SH;

[0137] R3, R4and R5are independently selected from each other and are a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C4to C4alkyl groups and / or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo;

[0138] R6is a C4-C4-alkyl group;

[0139] R7,R8and Rgare independently selected from each other and are a C4-C4-alkyl group;

[0140] R30and R31are independently from each other selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30and R31cannot both be hydrogen.

[0141] Clause 2: Method according to claim 1, wherein compound (la and / or

[0142] (lb) are selected from the group consisting of:

[0143]

[0144] Clause 3: Method according to clause 1, wherein the reaction is carried out under neat conditions.

[0145] Clause 4: Method according to clause 1, wherein the reaction is carried out in a solvent, preferably in a solvent selected from the group consisting of dimethylisosorbide, cyclic ethers, in particular 1,4-dioxane or 2-methyltetrahydrofuran, sulfolane, sulfolene, aliphatic acids in particular acetic acid, alkylpyrrolidone, cyclic carbonates, cyclic esters, in particular y-valerolactone or y-gamma butyrolactone, acetonitrile and non-cyclic ethers, in particular diethyl ether, mono ethylene, diethylen, triethylene, triethylene glycol mono / di ethers.

[0146] Clause 5: Method according to any of the preceding clauses, wherein unreacted compound of formula (la) and / or (lb) is recycled by means of distillation.

[0147] Clause 6: Method according to any of the preceding clauses, wherein Z in compound (la) and (lb) is absent.

[0148] Clause 7: Method according to any of the preceding clauses, wherein R30and R31are the same.

[0149] Clause 8: Method according to any of the preceding clauses, wherein Z is -CH2or absent; X is Cl, Br or -COOR3; and R3is -CH3or -CH2CH3.

[0150] Clause 9: Method according to any of the preceding clauses, wherein

[0151] R30, R31and R3are the same. Clause 10: Method according to any of the preceding clauses for preparing an acetal protected fragment of lignin having one or more functional groups -Z-COOR3.

[0152] Clause 11: Method according to any of the preceding clauses, wherein the catalyst is a homogenous catalyst.

[0153] Clause 12: Method according to clause 11, wherein the homogenous catalyst is an organic or an inorganic acid, preferably selected from the group consisting of H2SO4, H3PO4, HBr, HC1, phosphotungstic acid, phosphomolybdic acid, tungstosilicic acid, methano sulfonic acid, and para-toluene sulfonic acid.

[0154] Clause 13: Method according to any of clauses 1 to 10, wherein the catalyst is a heterogeneous catalyst.

[0155] Clause 14: Method according to any of the preceding clauses, wherein the heterogeneous acidic catalyst is a Bronsted acidic catalyst, preferably selected from the group consisting of a. acidic zeolite, b. acidic doped zeolite, c. acid site-functionalized resin, d. acid site-functionalized oxide, e. acidic oxide, and f. Immobilized versions of the homogeneous acids specified in clause 11, preferably silica sulfuric acid.

Claims

Claims1. Method for preparing an acetal-protected sugar involving the step of reacting a diol group of a sugar selected from the group consisting of an aldopentose and an aldohexose with one or two compounds of formula (la) and / or (lb)in the presence of a homogenous or heterogenous catalyst to form an acetal-protected sugar selected from the group consisting of a compound of formula (II), (III) and (IV)(IDwherein R4and / or R2are independent from each other -Z-X, and wherein Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 C4- C4-alkyl groups or 1 to 4 halogen atoms, or -B-D, whereinB is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent, D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 Ci-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3groups or 1 to 4 halogen atoms and combinations thereof, and whereinZ may be present or absent, and X is -COOH, -CH(COOH)2, -COOR3, CHO, -C2H3, -C2H, -CHOR4OR5, -N3, -NHR6, -NR7R8, -F, -Cl, -Br, -I, or if Z is present, -OH, NH2, or -SH;R3, R4 and R5are independently selected from the group consisting of a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C3to C4alkyl groups and / or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo;R6is a Ci-C4-alkyl group;R7, R8and Rgare independently from each other a C!-C4-alkyl group;R30and R31are independently selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30and R31cannot both be hydrogen;Rio is independently selected from the group consisting of -H, -OH, -CH2OH, -OR13or -CH2OR15;Rn and R12are independently selected from the group consisting of -OH or -OR13;R13JR14and R15are independently selected from a hydrocarbon moiety with 1 to 10 carbon atoms; and n and p are independently from each other either 0 or 1.

2. Method according to claim 1, wherein compound (la) and / or (lb) are selected from the group consisting of:

3. Method according to claim 1, wherein the reaction is carried out under neat conditions.

4. Method according to claim 1, wherein the reaction is carried out in a solvent, preferably in a solvent selected from the group consisting of dimethylisosorbide, cyclic ethers, in particular 1,4-dioxane or 2-methyltetrahydrofuran, sulfolane, sulfolene, aliphatic acids in particular acetic acid, alkylpyrrolidone, cyclic carbonates, cyclic esters, in particular y-valerolactone or y-gamma butyrolactone, acetonitrile and non-cyclic ethers, in particular diethyl ether, mono ethylene, diethylen, triethylene, triethylene glycol mono / di ethers.

5. Method according to any of the preceding claims, wherein unreacted compound of formula (la) and / or (lb) is recycled by means of distillation.

6. Method according to any of the preceding claims, wherein Z in compound (la) and (lb) is absent.

7. Method according to any of the preceding claims, wherein R30and R31are the same.

8. Method according to any of the preceding claims, wherein Z is-CH2or absent; X is Cl, Br or -COOR3; and R3is -CH3or -CH2CH3.

9. Method according to any of the preceding claims, wherein R30,R3Iand R3are the same.

10. Method according to any of claims 1 to 9 for preparing compound(ID •11. Method according to any of claims 1 to 9 for preparing compounds(Ill) or (IV).

12. Method according to any of the preceding claims, wherein thecatalyst is a homogenous catalyst.

13. Method according to claim 12, wherein the homogenous catalyst is an organic or an inorganic acid, preferably selected from the group consisting of H2SO4, H3PO4, HBr, HC1, phosphotungstic acid, phosphomolybdic acid, tungstosilicic acid, methano sulfonic acid, and para-toluene sulfonic acid.

14. Method according to any of claims 1 to 11, wherein the catalyst is a heterogeneous catalyst.

15. Method according to any of the preceding claims, wherein the heterogeneous acidic catalyst is a Bronsted acidic catalyst, preferably selected from the group consisting of g. acidic zeolite, h. acidic doped zeolite, i. acid site-functionalized resin, j. acid site-functionalized oxide, k. acidic oxide, and l. Immobilized versions of the homogeneous acids specified in claim 12, preferably silica sulfuric acid.

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