PROCESS FOR PREPARATION OF 2,5-DISUBSTITUTED FURANES, PRODUCT OBTAINED AND ITS USES

Abstract

The present invention relates to a process for preparing 2,5-disubstituted furans possessing aldehyde and / or ester and / or carboxylic acid and / or acetal functional groups, which are oxidizable, hydrolyzable, or saponifiable. The present invention also relates to 5-(dihydroxymethyl)furan-2-carboxylic acid and its use in the preparation of biopolymers, particularly 2,5-furandicarboxylic acid (FDCA).

Description

Title of the invention: METHOD FOR PREPARING 2,5-DISUBSTITUTED FURANES, PRODUCT OBTAINED AND ITS USES technical field

[0001] The present invention relates to a process for preparing 2,5-disubstituted furans having aldehyde and / or ester and / or carboxylic acid and / or acetal functions, oxidizable, hydrolyzable or saponifiable, as well as to 5-(dihydroxymethyl)furan-2-carboxylic acid and its use in the preparation of biopolymers, in particular 2,5-furandicarboxylic acid (FDCA).

[0002] The present invention finds applications particularly in the field of industrial chemistry, especially in the field of polymers.

[0003] In the description below, references in brackets ([ ]) refer to the list of references presented at the end of the text. State of the art

[0004] Bio-based 2,5-disubstituted furan derivatives are now emerging as key molecules for the production of innovative biopolymers as biodegradable alternatives to petroleum-based polymers. In particular, polyethylene 2,5-furandicarboxylate, or PEF for short, is a new bio-based polymer whose chemical structure bears a strong resemblance to that of petrochemical-derived polyethylene terephthalate (PET). It is produced by polycondensation of the monomers FDCA (2,5-furandicarboxylic acid) and MEG (mono-ethylene glycol), in a manner analogous to the polycondensation of the raw materials used to produce PET. Most of the processes for the synthesis of 2,5-furandicarboxylic acid (FDCA) are based on the transformation of fructose or glucose into HMF (hydroxymethylfurfural) or MMF (methoxymethylfurfural) followed by 3 oxidation reactions.Developing new FDCA production routes remains an important challenge, particularly in order to bypass the chemically unstable HMF step and / or improve the oxidation step (searching for milder conditions) leading to the formation of the two carboxylic acid functions.

[0005] In the literature, several potential furanic precursors of FDCA, other than HMF, have been reported, such as butyl 5-formyl-2-furoate (BFF), 5-formyl-2-furancarboxylic acid (FFA), and butyl 5-(dibutoxymethyl)-2-furoate (BDMF), which possess aldehyde and / or ester and / or carboxylic acid and / or acetal functional groups that are oxidizable, hydrolyzable, or saponifiable. The production of BFF described in document WO 2017 / 030668 ([1]) uses derivatives as raw materials. Gluconic acid (dehydrogluconic acid, DHG; 2-ketogluconic acid, 2KGA; 5-ketogluconic acid, 5KGA) is formed via an enzymatic transformation of gluconate. As described in WO 2013 / 049711 ([2]), FFA can be synthesized by a dehydration reaction followed by cyclization from 4-deoxy-L-erythro-5-hexosulose uronate (DEHU) or 4-deoxy-L-threo-5-hexosulose uronate (DTHU), obtained by chemical or biological transformation of polysaccharides such as alginates and pectins. Enzymatic digestion of algal biomass can also lead to FFA in mixtures with two other furanic derivatives, 5-hydroxymethylfurfural (HMF) and 2,5-dihydroxymethylfuran (DHMF).

[0006] More recently, a process for synthesizing BDMF was developed (document EP3560916A1 ([3]); L. Renault et al. ([4])) from mono-, oligo-, or polysaccharide hydrolysates for the production of bio-based surfactants. This strategy requires a preliminary step of extracting polysaccharides from biomass, followed by a depolymerization step in the case of using oligo- and monosaccharides. Thus, this process is not suitable for use with raw plant material. Indeed, applying the conditions of the process in this patent to algal biomass does not allow the formation of 2,5-disubstituted furanic derivatives such as BDMF, or only in trace amounts.

[0007] Thus, these strategies rely on generally costly processes related to the raw materials and / or chemical or biological reagents used, the need to isolate reaction intermediates or the purification methods implemented.

[0008] There is therefore a real need for a new process for preparing FDCA or its precursors which overcomes these defects, disadvantages and obstacles of the prior art, in particular a process which is simpler to implement and which reduces production costs.

[0009] Description of the invention

[0010] The present invention is specifically designed to address these needs and drawbacks of the prior art.

[0011] The inventors of the present have indeed developed a process for the synthesis of 2,5-disubstituted furans from raw plant materials, as precursors of 2,5-furandicarboxylic acid (FDCA).

[0012] The inventors have notably developed a direct process for transforming raw plant material, making it possible to isolate furanic derivatives consisting exclusively of ester, carboxylic acid, acetal or aldehyde functions, without resorting to biological processes, without going through isolation and / or steps. purification of reaction intermediates and using simple purification methods to implement.

[0013] Another advantage is that the polysaccharides contained in the raw plant material are depolymerized in situ to lead to alcoholyse and / or hydrolysis products without requiring a prior extraction step.

[0014] Advantageously, the furanic compounds obtained do not contain an alcohol-type substituent that would require harsher oxidation conditions to form the carboxylic acid functions of FDCA.

[0015] Particularly advantageously, the process of the invention is applicable to different sources of polysaccharides, including pectins which are abundant in many inexpensive plant materials, without significantly altering the efficiency of obtaining these compounds, even though it is well established that it is difficult to control the complete hydrolysis of pectins.

[0016] Thus, a first object of the invention relates to a process for preparing 2,5-disubstituted furans having aldehyde and / or ester and / or carboxylic acid and / or acetal functions, oxidizable, hydrolyzable or saponifiable, comprising the following steps: a. the reaction of a crude plant material with at least one alcohol of formula R-OH where R designates a linear or branched C1-C6 alkyl group in the presence of at least one acid catalyst and possibly water, under conditions allowing to obtain a first mixture containing polysaccharide depolymerization products, b. Filtration at a temperature between approximately 18 and approximately 25°C of the first mixture using an amount of alcohol of formula R'-OH, where R' denotes a linear or branched C1-C6 alkyl group, of no more than 10 times that used in step (a), to produce a second mixture free of insoluble residues, c. the dehydration of the polysaccharide depolymerization products of said second mixture after the addition of an additional quantity of acid catalyst, under conditions leading to a third mixture containing alkyl 5-dialkylacetal-2-furoates whose alkyl chains are derived from alcohol of formula R-OH and / or alcohol of formula R'-OH, d. Neutralization of the third mixture at a temperature between approximately 18 and approximately 25°C with a base to a pH between approximately 6 and approximately 7, followed by concentration under reduced pressure, to produce a residue, e. the recovery of said residue in a nonpolar solvent, followed by filtration and washing with the nonpolar solvent until total transfer of the compounds furanic compounds in the filtrate, allowing the removal of insoluble polar compounds. f. Concentration of the filtrate under pressure between approximately 15 and approximately 50 mbar followed by distillation under pressure between approximately 0.05 and approximately 0.5 mbar, allowing the removal of the solvent and volatile monosubstituted furanic co-products such as alkyl 2-furoates, to lead to a composition enriched in 5-dialkylacetal-2-alkyl furoates, g. the saponification of the composition containing alkyl 5-dialkylacetal-2 furoates, h. acidification of the saponified composition with an aqueous solution of acid followed by washing of the organic phase, leading to 5-dialkylacetal-2-carboxylic acids, or without washing of the organic phase, leading to 5-formylfuran-2-carboxylic acid (FFA) and 5-(dihydroxymethyl)furan-2-carboxylic acid.

[0017] A second object of the invention relates to a compound of formula (V):

[0018] 5-(dihydroxymethyl)furan-2-carboxylic acid

[0019] Another object of the invention relates to the use of the compound of formula (V) in the preparation of biopolymers, in particular 2,5-furandicarboxylic acid (FDCA).

[0020] For the purposes of this invention, "2,5-disubstituted furans" means any heterocyclic chemical compound with the molecular formula C4H4O, consisting of a five-atom aromatic ring, including one oxygen atom, and substituted at positions 2 and 5. The two substituents are selected from aldehyde, ester, carboxylic acid, and acetal functional groups. In other words, each of the two substituents is selected independently from among aldehyde, ester, carboxylic acid, and acetal functional groups. Thus, a 2,5-disubstituted furan as defined in this invention may include, for example: - two aldehyde functions, or two ester functions, or two carboxylic acid functions, or two acetal functions, different or identical, or - an aldehyde function and a function chosen from among an ester function, a carboxylic acid function and an acetal function, or - an ester function and a function chosen from a carboxylic acid function and an acetal function, or - a carboxylic acid function and an acetal function.

[0021] For the purposes of this invention, "ester function" means any carboxylic ester function in which the alkyl group from the alcohol can be selected from a linear or branched C1-C6 alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl or hexyl.

[0022] For the purposes of this invention, the term "acetal function" means any acetal function comprising two alkoxyl groups, each having a linear or branched, saturated or unsaturated C1-C6 alkyl group, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, or hexyl. The alkyl groups attached to the acetal function may be different if several alcohols are used in the process, or identical if only one alcohol is used.

[0023] For example, the 2,5-disubstituted furans that can be obtained by implementing the process of the invention can be at least the following: alkyl 5-dialkylacetal-2-furoate, 5-dialkylacetal-2-carboxylic acid, 5-formylfuran-2-carboxylic acid (FFA), 5-(dihydroxymethyl)furan-2-carboxylic acid and FDCA, the obtaining of the latter compound being subject to additional reaction steps.

[0024] For the purposes of this invention, "raw plant material" means any plant material that has not undergone any chemical transformation, in particular extraction using a solvent or by enzymatic means, from its natural state. At most, it may have undergone some mechanical and / or physical transformation, such as washing, grinding, and / or drying. Optionally, the raw material may be pre-dried and / or ground before step (a), particularly to facilitate its handling and / or storage. Advantageously, the raw plant material used may have a water content of less than 50% by weight, preferably less than 15% by weight, in order to promote the alcoholysis reaction rather than the hydrolysis reaction, and to facilitate the removal of this small amount of water in addition to that from the catalyst and that formed during steps a and c.Preferably, the raw plant material is chosen from those containing polysaccharides with glycosiduronic acid units, in particular from alginates, pectins and ulvans. Examples of glycosiduronic acid include guluronic acid, mannuronic acid, galacturonic acid, glucuronic acid, iduronic acid, glucurono-6,3-lactone, and mixtures thereof.

[0025] Thus, more specifically, the raw plant material can be chosen from: - Brown algae, which may be, for example, at least one alga chosen from Ascophyllum, Durvillaea, Ecklonia, Laminaria, Lessonia, Macrocystis, Sargassum and Turbinaria. Advantageously, these algae contain alginates that include blocks of 3-D-mannuronic acid and / or α-L-guluronic acid. - Green algae of the Ulva or Enteromorpha type, which may include, for example, at least one alga selected from the species Ulva armoricana, Ulva rigida, Ulva rotundata, Ulva lactica, Ulva linza, Enteromorpha intes tinalis, and Enteromorpha compressa. Advantageously, these algae contain ulvans that include D-glucuronic acid and L-iduronic acid units. - Beet pulp, as well as the skin, peel, and / or seeds of fruits such as citrus fruits and / or apples. Advantageously, these plant materials contain pectin, which includes acidic units for several reasons: α-galacturonic acid. - and mixtures thereof.

[0026] As indicated above, in the first step of the process of the invention, the raw plant material is reacted with at least one alcohol of formula R-OH, where R denotes a linear or branched C1-C6 alkyl group. As such, the at least one alcohol usable in this step of the process can be chosen from methanol, ethanol, propanol, isopropanol, butanol, pentanol, 3-methylbutanol (or isoamyl alcohol), hexanol, and mixtures thereof. In this description, "butanol" includes n-butanol, isobutanol, and .sec-butanol. Butanol, and more particularly n-butanol, is preferred for use in this invention for several reasons: it has a sufficiently high boiling point (118°C) to ensure high reactivity at this temperature; it can be easily removed by distillation at atmospheric pressure; It allows water to be easily removed via azeotropic distillation.In this step, if a mixture of alcohols is used, it may comprise 2, 3, 4, or more than 4 different alcohols. The quantity of at least one alcohol may be between approximately 5 and approximately 500% by weight, preferably between approximately 150 and approximately 250% by weight, relative to the mass of raw plant material used in step (a).

[0027] The at least one acid catalyst used in step (a) can be any acid catalyst known to those skilled in the art. For example, it could be at least one catalyst chosen from among homogeneous catalysts such as a Brønsted acid or a Lewis acid, and heterogeneous catalysts.

[0028] If it is a Brønsted acid, it can, for example, be chosen from inorganic acids such as hydrochloric acid, sulfuric acid, perhalohydrogen acids, such as perchloric acid, and mixtures thereof. Alternatively, the acid catalyst can be chosen from organic acids, such as alkyl sulfuric acids, for example decyl or lauryl sulfuric acid, arylsulfonic acids, such as benzenesulfonic acid and para-toluenesulfonic acid, alkylsulfonic acids, such as triflic acid, methanesulfonic acid, and so on. ethanesulfonic acid, decylsulfonic acid and laurylsulfonic acid, camphosulfonic acid, and mixtures thereof. Preferably, alkylsulfonic acid such as methanesulfonic acid, for several reasons: it is highly soluble in water, forming a homogeneous solution and miscible with most polar organic solvents (e.g., butanol); it is a weaker acid than sulfuric acid, which helps to limit unwanted reactions; and it is biodegradable.

[0029] Lewis acids can in particular be chosen from copper, silver, manganese, iron, magnesium or aluminum halides or compounds of formula ZnX2, SnX2, SnX4 and SiX4 where the X groups designate, independently of each other, a halogen atom or an alkyl, cycloalkyl, alkenyl, phenyl or benzyl group.

[0030] If it is a heterogeneous catalyst, it may be at least one catalyst selected from zeolites, ion-exchange resins, such as Amberlyst® (Thermo Scientific Chemicals) and Nafion® resins, functionalized mesoporous silicas, functionalized carbons, supported and functionalized metal oxides, heteropolyacids, and mixtures thereof. Particularly advantageously, it may be a cation-exchange resin with strong acid groups, especially sulfonic acid, grafted onto polystyrene or a styrene copolymer, possibly crosslinked with divinylbenzene, such as Amberlyst-15® resin (Thermo Scientific Chemicals).

[0031] In this step, if a mixture of acid catalysts is used, it may comprise 2, 3, 4, or more than 4 different catalysts. At least one catalyst may be used in an amount of between 5 and 50% by weight, preferably between 15 and 35% by weight, relative to the mass of the raw plant material used.

[0032] Preferably, this reaction is carried out in the absence of any solvent other than alcohol. In this embodiment, step (a) of the process is therefore conducted in the absence of water other than that supplied by the reactants, in particular the catalyst. Alternatively, if water is present, the amount of water present in this step is such that the weight ratio of water to plant matter is at most 1:1, advantageously at most 0.3:1.

[0033] The conditions for obtaining a first mixture containing polysaccharide depolymerization products can be selected by a person skilled in the art, based on their general knowledge. For example, this first step can be carried out at atmospheric pressure and at a temperature above the boiling point of the solvent. For instance, the solvent can be refluxed. Step (a) of the process can thus be conducted at a temperature ranging from 80 to 140°C, preferably from 100 to 140°C, more preferably from 120 to 140°C, for a duration, for example, of 3 to 24 hours, preferably from 12 to 18 hours. This step is to The mixture is preferably prepared under mechanical stirring. The resulting mixture contains depolymerization products, particularly from alcoholysis and / or hydrolysis, of polysaccharides. The polysaccharide depolymerization products may be, for example, monomers with a molar mass of 194.14 g / mol (hydrolysis product) or with a molar mass between 222 and 363 g / mol (alcoholy product with C1-C6 alcohols), or oligomers with molar masses less than 1600 g / mol. Any known method for detecting, identifying, and / or quantifying depolymerization products may be used, such as size-exclusion chromatography, mass spectrometry, spectroscopy, neutron scattering, or small-angle X-ray scattering.

[0034] In step (b), filtration can be any known type of filtration that removes the insoluble residues present in the first mixture obtained at the end of step (a). For the purposes of this invention, "free of insoluble residues" means a mixture containing less than 1% by mass of insoluble residues relative to the total mass of the second mixture. The insoluble residues can be, for example, salts and / or fibers contained in the raw plant material, although this list is not exhaustive. Any known method for detecting, identifying, and / or quantifying these insoluble residues can be used, such as thermogravimetric analysis (TGA) to determine the proportions of moisture, organic matter, and inorganic matter.The filtration process can be, for example, a selected filtration method, such as diatomaceous earth filtration, Buchner-type filtration, or sintered glass filtration, and an industrial liquid-solid separation device, such as centrifugation. Preferably, it is diatomaceous earth filtration. The conditions of the filtration step can be selected by a person skilled in the art based on their general knowledge.

[0035] In the alcohol of formula R'-OH used in step (b), R' designates a linear or branched C1-C6 alkyl group as defined above in the context of step (a). Accordingly, at least one alcohol usable in this step of the process may be selected from methanol, ethanol, propanol, isopropanol, butanol, pentanol, 3-methylbutanol (or isoamyl alcohol), hexanol, and mixtures thereof. "Butanol" in this description includes n-butanol, isobutanol, and sec-butanol. Butanol, and more particularly n-butanol, is preferred. In this step, if a mixture of alcohols is used, it may comprise two, three, four, or more than four different alcohols.

[0036] The at least one alcohol used in step (b) may be the same as that used in step (a), or it may be different. For example, the alcohol used in both step (a) and step (b) may be butanol. As stated above, the amount of alcohol R'-OH used in step (b) is at most 10 times greater, for example at most 9 times, or at most 8 times, or at most 7 times, or at most 6 times, or preferably at most 5 times greater, than that used in the first step.

[0037] The filtration step is essential because the mixture obtained after the first step is very viscous and the formation of furan derivatives in the next transformation step would not be possible without filtration, or only in trace amounts.

[0038] During the dehydration step (c), the additional amount of acid catalyst added can be determined by those skilled in the art to obtain a third mixture containing alkyl 5-dialkylacetal-2-furoates whose alkyl chains are derived from the alcohol of formula R-OH, using their general knowledge. The amount of acid catalyst added can, for example, be between 5 and 30% by weight, preferably between 5 and 10% by weight, relative to the mass of the raw plant material used. Similarly, the reaction conditions leading to the third mixture can be determined by those skilled in the art using their general knowledge. For example, step (c) can be carried out at a temperature between about 110 and 180°C, preferably between about 140 and about 160°C for a period of about 3 to 32 hours, preferably between 16 and 24 hours, or between 20 and 24 hours.Advantageously, the temperature of step (c) is higher than that of step (a), which favors the formation of furanic rings. The water initially present and / or formed during this step can be removed by any method known to those skilled in the art, such as azeotropic distillation using a Dean-Stark apparatus. The alkyl (I) 5-dialkylacetal-2-furoates of the third mixture have alkyl chains derived from or from alcohol(s) of formula R-OH present in steps (a) and (b), depending on whether the same alcohol of formula R-OH is used in steps (a) and (b) or a different alcohol of formula R-OH is used in steps (a) and (b). O (i) JD, 0-Rt v. r % # 5-Dialkylacetal-2-alkyl furoate

[0039] Thus, in alkyl(I) 5-dialkylacetal-2-furoates, Rb, R2, and R3 are, independently of each other, linear or branched, saturated or unsaturated alkyl chains, containing 1 to 6 carbon atoms, as described above with respect to the ester and acetal functional groups. In a particular embodiment, each of the RB groups R2 and R3 may be identical if an identical alcohol is used in steps (a) and (b) of the process. In this case, R=R'=Ri=R2=R3.

[0040] The neutralization step (d) can be carried out by adding a reaction base. Any base known to those skilled in the art can be used, such as sodium hydroxide, sodium bicarbonate, or calcium carbonate; this list is not exhaustive. The absence of this neutralization step may lead to degradation of the 2,5-disubstituted furan derivative of interest. The concentration of the reaction mixture following neutralization is carried out under reduced pressure, i.e., at a pressure between 15 and 50 mbar.

[0041] In step (e), the nonpolar solvent used can be any nonpolar solvent known to those skilled in the art, such as cyclohexane, pentane, or hexane. The amount of nonpolar solvent added can be determined by those skilled in the art based on their general knowledge. The filtration in step (e) can be of the type described above for step (b). The total transfer of furanic compounds into the nonpolar solvent can be determined by any analytical method known to those skilled in the art, such as gas chromatography coupled with mass spectrometry, high-performance liquid chromatography, UV-visible spectroscopy, or nuclear magnetic resonance (NMR), this list being non-exhaustive.

[0042] In step (f), the concentration of the filtrate under reduced pressure, between approximately 15 and approximately 50 mbar, allows the nonpolar solvent to be eliminated, meaning that it is present in the subsequent stages of the process at a concentration of no more than 5% by mass relative to the total mass of the concentrated filtra. The pressure can be, for example, approximately 15 mbar, or approximately 20 mbar, or approximately 30 mbar, or approximately 40 mbar, or approximately 50 mbar.

[0043] Distillation under a higher vacuum, corresponding to a pressure between approximately 0.05 and approximately 0.5 mbar, makes it possible to eliminate volatile compounds, and in particular volatile monosubstituted furanic co-products such as alkyl(II) 2-furoates, as well as residual solvents, leading to a composition enriched in alkyl 5-dialkylacetal-2-furoates. The pressure can be, for example, approximately 0.05 mbar, or approximately 0.07 mbar, or approximately 0.09 mbar, or approximately 1.0 mbar, or approximately 1.2 mbar, or approximately 1.5 mbar. alkyl 2-furoate

[0044] Step (f) can be carried out at any temperature allowing the concentration and distillation described above, and preferably at room temperature, i.e. between about 18 and about 25°C, because using a higher temperature, for example 40°C, results in a decrease in the amount of the isolated 2,5-disubstituted furan derivative of interest.

[0045] At the end of this step, we obtain a composition enriched in alkyl 5-dialkylacetal-2-furoates of formula (I) as defined above, i.e. comprising a concentration of alkyl 5-dialkylacetal-2-furoates greater than that of the mixture from step (e).

[0046] Of course, if the desired compound is an alkyl 5-dialkylacetal-2-furoate, it is not necessary to carry out the following steps, namely (g) and (h).

[0047] Step (g) of saponification of the composition containing the alkyl 5-dialkylacetal-2-furoates can be carried out by any method known to those skilled in the art, for example by introducing into the composition an alcohol of formula R”-OH where R” denotes a linear or branched C1-C6 alkyl group, as described above with respect to R or R'. Examples of alcohols that can be used in this step of the process are methanol, ethanol, propanol, isopropanol, butanol, pentanol, 3-methylbutan-l-ol (or isoamyl alcohol), hexanol, and mixtures thereof. For the purposes of this description, “butanol” includes n-butanol, isobutanol, and sec-butanol. Preferably, the alcohol used in this step is methanol. This saponification step can be carried out by adding 2 to 50 equivalents and preferably 20 to 30 equivalents of a base such as sodium hydroxide, potassium hydroxide, ammonia or an alkyl (hydroxyalkyl) ammonium hydroxide.The saponification reaction of esters is preferably carried out at a temperature between 0 °C and 150 °C, and preferably between 100 and 120 °C, for a duration of 15 minutes to 24 hours, and preferably for 30 minutes to 5 hours.

[0048] Advantageously, the composition enriched in alkyl 5-dialkylacetal-2-furoates can be subjected to liquid-liquid extraction with a medium-polarity organic solvent, such as alkyl acetates, particularly methyl, ethyl, isopropyl, butyl, and preferably ethyl acetate, and alkyl lactates such as ethyl lactate. The aqueous phase resulting from this extraction may contain salts of 5-dialkylacetal-2-furoic acid.

[0049] The step (h) of acidifying the saponified composition, or the aqueous phase containing the salts of 5-dialkylacetal-2-furoic acid, with an aqueous solution of acid, can be carried out under conditions which a person skilled in the art can determine according to their general knowledge, in order to obtain furanic derivatives with carboxylic acid and acetal or aldehyde functions.

[0050] For example, the acidification of the aqueous phase can be carried out with an aqueous solution of acid up to a pH value of 2. Among the acids used will be Brønsted acids selected from inorganic acids such as hydrochloric acid,

[0051]

[0052]

[0053]

[0054]

[0055]

[0056] sulfuric acid, perhalohydrogen acids, such as perchloric acid, and mixtures thereof. Alternatively, when acidification is followed by washing, the acid can be chosen from among organic acids, such as oxalic acid, maleic acid, and fumaric acid. Preferably, acids with a pKa between 1 and 4, preferably between 1 and 2, such as oxalic acid, maleic acid, and preferably oxalic acid, should be chosen in order to avoid hydrolyzing the acetal function while ensuring the protonation of the carboxylate groups. In another variant, when acidification is not followed by washing, the acid may be chosen from among organic acids, such as alkyl sulfuric acids, for example decyl or lauryl sulfuric acid; arylsulfonic acids, such as benzenesulfonic acid and para-toluenesulfonic acid; alkylsulfonic acids, such as triflic acid, methanesulfonic acid, ethanesulfonic acid, decylsulfonic acid, laurylsulfonic acid; camphosulfonic acid and mixtures thereof. Preferably, in this embodiment, a strong inorganic acid (pKa less than 1) such as hydrochloric acid is chosen to facilitate the hydrolysis of the acetal group. Whether or not a washing step is carried out, the aqueous phase resulting from acidification can be extracted with a medium polarity organic solvent, such as alkyl acetates, including methyl, ethyl, isopropyl, butyl, and preferably ethyl acetate and alkyl lactates such as ethyl lactate. In the embodiment including washing, this can be carried out with water. For example, the organic phase resulting from acidification can be washed with water until neutralization (pH close to 7) then dried and concentrated under reduced pressure at ambient temperature, namely between approximately 18 and 25 °C. In the embodiment not including washing, the organic phase can then be dried and concentrated under reduced pressure at 40°C. In the embodiment in which a washing step is present, a composition comprising at least one 5-dialkylacetal-2-carboxylic acid of formula (III) is thus isolated, where Ri and R2 are linear or branched, saturated or unsaturated alkyl chains, containing 1 to 6 derived carbon atoms, as defined above. However, it is possible that each of the Ri and R2 groups may be replaced by the same R group if a Only alcohol is used in the process, as explained above. (III) 5-Dialkylacetal-2-carboxylic acid

[0057] In the embodiment in which the organic phase is not washed, 5-formylfuran-2-carboxylic acid or FFA (IV) and 5-(dihydroxymethyl)furan-2-carboxylic acid (V) are obtained. 5-Formylfuran-2-Carboxylic acid or FFA 5-(dihydroxymethyl)furan-2-carboxylic acid

[0058] Thus, at the end of its implementation, the preparation process according to the invention makes it possible to obtain compositions comprising at least one 5-dialkylacetal-2-furoate, and / or one 5-dialkylacetal-2-carboxylic acid and / or one 5-formylfuran-2-carboxylic acid and / or one 5-(dihydroxymethyl)furan-2-carboxylic acid.

[0059] These disubstituted 2,5-furan compounds, and in particular FFA, can be transformed into biopolymers, notably FDCA, by means of a process known to those skilled in the art. This may be, for example, the process and oxidation conditions described in document WO 2013 / 049711 ([2]).

[0060] Other advantages may also become apparent to a person skilled in the art upon reading the examples below, illustrated by the attached figures, given for illustrative purposes.

[0061] Examples

[0062] Example 1: Synthesis of butyl(I) 5-dibutylacetal-2-furoate from crude algae and butanol

[0063] Dried and ground raw seaweed Ascophyllum nodosum (Thorverk's Asco T30) (5.0 g, 1.0 eq.) was dispersed in butanol (14 mL, 2.8 v / w eq.) and a 70% methanesulfonic acid solution (1.15 mL, 0.23 v / w eq.) was added. The mixture was heated to 135 °C with vigorous stirring. After 16 hours of reaction, the solution was filtered through Celite. Butanol (70 mL, 14 v / w eq.) and 70% methanesulfonic acid (0.3 mL, 0.06 v / w eq.) were added and the mixture was heated to 155 °C. The water present in the medium was gradually removed by azeotropic distillation using a Dean-Stark apparatus. After an additional 24 hours of reaction, the mixture was allowed to return to room temperature. The reaction medium was then neutralized with a 0.5 M aqueous NaOH solution (6.5 mL, pH 6–7) and subsequently concentrated and The product was dried under reduced pressure. The residue was resuspended in cyclohexane and filtered through Celite, then washed with cyclohexane until the desired product disappeared from the filtrate (1.4 g of insoluble compounds were removed). The filtrate was concentrated under reduced pressure and dried on a vacuum manifold (0.062 bar). A product mixture (1.2 g) was obtained, containing butyl 5-dibutylacetal-2-furoate (133.6 mg, 12% by mass of the mixture) and residual sugars.

[0064] 1 H NMR (400 MHz, CDC13) ô 7.19 (d, J = 3.5 Hz, 1H), 6.52 (d, J = 3.4 Hz, 1H), 5.54 (s, 1H), 4.29 (t, J= 6.7 Hz, 2H), 3.60-3.50 (m, 4H), 1.79-1.71 (m, 2H), 1.64-1.57 (m, 4H), 1.49-1.33 (m, 6H), 0.98 (t, J = 7.2 Hz, 3H), 0.94 (t, J= 7.2 Hz, 6H).

[0065] Example 2: Synthesis of 5-dibutylacetal-2-carboxylic acid (III) from a mixture containing butyl 5-dibutylacetal-2-furoate obtained from the processing of crude algae

[0066] A mixture (1.2 g) containing butyl 5-dibutylacetal-2-furoate (126.4 mg, 11% by mass of the mixture) along with butanol and residual sugars (as obtained from the process of Example 1) was dispersed in methanol (38 mL, c=0.01 M) and an aqueous solution of IM NaOH (12 mL, 30 eq.) was added. The mixture was heated to 110 °C with vigorous stirring. After 1 hour of reaction, the reaction was extracted with a water / ethyl acetate mixture at room temperature. The aqueous phase was acidified with a 0.5 M aqueous oxalic acid solution (18 mL, pH 2). The aqueous phase was extracted with ethyl acetate and then the organic phase was washed with water to pH 7. The organic phase was dried with MgSO4, filtered and concentrated under reduced pressure at room temperature and dried on the vacuum ramp (0.062 bar).A mixture of products (317mg) was obtained containing 5-dibutylacetal-2-carboxylic acid (64.9mg, 20% by mass of the mixture, 62% yield compared to butyl 5-dibutylacetal-2-furoate).

[0067] 1 H NMR (400 MHz, CDC13) ô 7.12 (d, J = 3.4 Hz, 1H), 6.56 (d, J = 3.5 Hz, 1H), 5.57 (s, 1H), 3.60-3.56 (m, 4H), 1.63-1.54 (m, 4H), 1.47-1.38 (m, 4H), 0.94 (t, J= 7.2 Hz, 6H).

[0068] Example 3: Synthesis of 5-formylfuran-2-carboxylic acid (V) from a mixture containing butyl 5-dibutylacetal-2-furoate obtained from the processing of crude algae

[0069] A mixture (0.700 g) containing butyl 5-dibutylacetal-2-furoate (77.0 mg, 11% by mass of the mixture) as well as butanol and residual sugars (as obtained from the process of Example 1) was dispersed in methanol (23 mL, c = 0.01 M) and an aqueous solution of IM NaOH (7 mL, 30 eq.) was added. The mixture was heated to 110 °C with vigorous stirring. After 1 hour of reaction, the reaction was extracted with a water / ethyl acetate mixture at room temperature. The aqueous phase was acidified with a 2M aqueous hydrochloric acid solution (6 mL, pH 2). The aqueous phase was extracted with ethyl acetate. The organic phase was dried with MgSO4, filtered, and concentrated under reduced pressure at 40 °C and dried on a vacuum ramp (0.062 bar). A mixture of products (431 mg) was obtained containing 5-formylfuran-2-carboxylic acid (11.4 mg, 3% by mass of the mixture, 34% yield compared to butyl 5-dibutylacetal-2-furoate) and 5-(dihydroxymethyl)furan-2-carboxylic acid (16.3 mg, 4% by mass of the mixture, 44% yield compared to butyl 5-dibutylacetal-2-furoate).

[0070] 1 H NMR (400 MHz, CDC13) ô 9.74 (s, 1H), 7.45 (d, J = 3.7 Hz, 1H), 7.34 (d, J = 3.5 Hz, 1H).

[0071] Example 4: Synthesis of butyl(I) 5-dibutylacetal-2-furoate from beet pulp and butanol

[0072] Beet pulp (5.0 g, 1.0 eq.) was dispersed in butanol (14 mL, 2.8 v / w eq.) and a 70% methanesulfonic acid solution (1.15 mL, 0.23 v / w eq.) was added. The mixture was heated to 135 °C with vigorous stirring. After 16 hours of reaction, the solution was filtered through Celite. Butanol (80 mL, 16 v / w eq.) and 70% methanesulfonic acid (0.3 mL, 0.06 v / w eq.) were added and the mixture was heated to 150 °C. The water present in the mixture was gradually removed by azeotropic distillation using a Dean-Stark apparatus. After a further 24 hours of reaction, the mixture was allowed to cool to room temperature. The reaction mixture was then neutralized with a 2M aqueous NaOH solution (9 mL, pH 6-7), concentrated, and dried under reduced pressure. The residue was resuspended in diethyl ether and filtered through Celite, then washed with diethyl ether until the desired product disappeared from the filtrate.The filtrate is concentrated under reduced pressure. After filtration through a silica column, a mixture of products (629 mg) was obtained containing butyl 5-dibutylacetal-2-furoate (80.7 mg, 13% by mass of the mixture) as well as residual sugars. Bibliographical references

[0073] - Reference 1: WO 2017 / 030668.

[0074] - Reference 2: WO 2013 / 049711.

[0075] - Reference 3: EP3560916

[0076] - Reference 4: L. Renault, R. Marchai, B. Le Guennic, X. Roussel, P.-Y. Divet, T. Benvegnu. Direct Conversion of Alginate Oligo- and Polysaccharides into Biodegradable and Non-Ecotoxic Anionic Furanic Surfactants-An Experimental and Mechanistic Study. Advanced Sustainable Systems, 2021, 2100108.

Claims

1. Demands A process for preparing 2,5-disubstituted furans having aldehyde and / or ester and / or carboxylic acid and / or acetal functions, oxidizable, hydrolyzable or saponifiable, comprising the following steps: a. the reaction of a crude plant material with at least one alcohol of formula R-OH where R designates a linear or branched C1-C6 alkyl group in the presence of at least one acid catalyst and possibly water, under conditions allowing to obtain a first mixture containing polysaccharide depolymerization products, b. Filtration at a temperature between approximately 18 and approximately 25 °C of the first mixture using an amount of alcohol of formula R'-OH, where R' denotes a linear or branched C1-C6 alkyl group, of no more than 10 times that used in step (a), to produce a second mixture free of insoluble residues, c. the dehydration of the polysaccharide depolymerization products of said second mixture after the addition of an additional quantity of acid catalyst, under conditions leading to a third mixture containing alkyl 5-dialkylacetal-2-furoates whose alkyl chains are derived from alcohol of formula R-OH and / or alcohol of formula R'-OH, d. Neutralization of the third mixture at a temperature between approximately 18 and approximately 25°C with a base to a pH between approximately 6 and approximately 7, followed by concentration under reduced pressure, to produce a residue, e. the recovery of said residue in a non-polar solvent, followed by filtration and washing with the non-polar solvent until total transfer of furanic compounds into the filtrate, allowing the elimination of insoluble polar compounds, f. Concentration of the filtrate under pressure between approximately 15 and approximately 50 mbar followed by distillation under pressure between about 0.05 and about 0.5 mbar, allowing the removal of the solvent and volatile monosubstituted furanic co-products such as alkyl 2-furoates, to lead to a composition enriched in alkyl 5-dialkylacetal-2-furoates, g. saponification of the composition containing alkyl 5-dialkylacetal-2-furoates, h. acidification of the saponified composition with an aqueous solution of acid followed by washing, leading to 5-dialkylacetal-2-carboxylic acids, or without washing of the organic phase, leading to 5-formylfuran-2-carboxylic acid (FFA) and 5-(dihydroxymethyl)furan-2-carboxylic acid.

2. A method according to claim 1, wherein step a) is carried out in the presence of water, in particular with a water-to-plant matter weight ratio of at most 1:

1.

3. A method according to claim 1 or 2, wherein step a) is carried out at a temperature of 80 to 140°C, for a period of 3 to 24 hours.

4. A method according to any one of the preceding claims, wherein the filtration of step b) and / or e) is selected from diatomaceous earth filtration, Buchner type filter filtration or sintered glass filtration, and an industrial liquid-solid separation device, for example centrifugation.

5. A method according to any one of the preceding claims, wherein step c) is carried out at a temperature of 110 to 180 °C, for a period of 3 to 32 hours.

6. A method according to any one of the preceding claims, wherein the washing in step h) is carried out with water.

7. A process according to any one of the preceding claims, wherein the plant material contains polysaccharides containing glycosiduronic acid units, in particular among alginates, pectins and ulvans.

8. A method according to any one of the preceding claims, wherein the plant material is at least one material selected from the group comprising brown algae, by Ascophyllum, Durvillaea, Ecklonia, Laminaria, Lessonia, Macrocystis, Sargassum and Turbinaria, green algae of the ulva or enteromorph type, for example Ulva armoricana, Ulva rigida, Ulva rotundata, Ulva lactica, Ulva linza, Enteromorpha intes tinalis and / or Enteromorpha compressa, beet pulp and the skin, peel and / or seeds of fruit such as citrus fruits and / or apples.

9. Compound of formula (V) obtained according to the process of claim 1: G (V) / JT ''GH

10. Use of the compound of formula (V) according to claim 9 in the preparation of biopolymers, in particular 2,5-furandicarboxylic acid (FDCA).