METHOD FOR THE PRODUCTION OF LOW-COLOR ALKYLPOLYGLYCOSIDES WITH PRE-NEUTRALIZATION OF THE REACTION MEDIUM

Description

[0001] The present invention relates to a process for preparing lightly coloured Alkyl Polyglycosides (colour less than 1.5 vcs) involving carbonate-type neutralizing agents.

[0002] Alkylpolyglycosides, or APGs, are probably the best examples of bio-based surfactants available on the market today. Their molecular structures are characterized by the simultaneous presence of a hydrophilic head derived from reducing sugars (D-glucose, D-xylose, or D-rhamnose are the reducing sugars mainly available on an industrial scale) and a more or less long lipophilic hydrocarbon chain (see formula I: simplified structure of an APG).

[0003] Their industrial-scale manufacturing process is relatively simple and uses as raw materials i) crystallized glucose, xylose, or rhamnose obtained respectively from the total hydrolysis of wheat, corn, or potato starch, or from the hydrolysis of wood hemicelluloses, and ii) fatty alcohols from the oleochemical process (hydrogenation of methyl esters resulting from the transesterification of vegetable triglycerides). Fischer glycosylation reactions then consist of linking these two raw materials together by creating a covalent chemical bond, as for example in reaction (II) between glucose and an alcohol.

[0004] To carry out this glycolyzation reaction, an acid catalyst of mineral or organic origin is required, and an excess of alcohols is systematically introduced, acting as both reactant and solvent. At the end of the reaction, the PGAs are dispersed or solubilized in the excess alcohol that did not react. PGAs are distinguished by the nature and length of their alkyl hydrocarbon chain R, as well as by their average Degree of Polymerization (DP), which is greater than 1 but less than or equal to 2.5.

[0005] Following the glycolysation reaction phase, a neutralization step is carried out in order to deactivate the catalyst and stop the reaction.

[0006] Depending on the length of the alkyl chain of the alcohol and the associated use, said alcohol is either removed or retained.

[0007] The neutralization step varies depending on the length of the alkyl hydrocarbon chain. If the chain has fewer than 12 carbon atoms, neutralization is carried out with an aqueous solution of sodium hydroxide. The excess fatty alcohols remaining after glycosylation are then removed by high-vacuum distillation or molecular distillation, or by evaporation, generally using a falling-film thin-film evaporator or a short-path thin-film evaporator. The resulting PGA concentrate is then dissolved in water. The commercial products obtained are therefore aqueous PGA solutions with a mass concentration between 40 and 80%.

[0008] In cases where the hydrocarbon alkyl chain R has 12 or more carbon atoms, neutralization is generally carried out with sodium hydroxide or potassium hydroxide, alone or in combination with a reducing agent as described in European patent EP0077167, European patent application EP0338151A1, and European patent EP0388857B1, such as sodium borohydride (NaBH4) or sodium hypophosphite (NaH2PO2). The mixture of PGA and excess fatty alcohols is isolated after neutralization and sold as is. The proportion of PGA and fatty alcohols depends on the initial molar stoichiometry of the raw materials and their reactivity. However, proportions of 5 to 30% by mass of PGA and 70 to 95% of fatty alcohols are generally observed.The resulting compositions can be in solid form, such as scales or beads, or in liquid form, depending on the nature of the alkyl hydrocarbon chain R.

[0009] However, the neutralization step of PGAs whose hydrocarbon alkyl chain R has a number of carbon atoms greater than or equal to 12 by a state-of-the-art base (e.g. NaOH, KOH), to achieve a pH value of a 5% mass dispersion in water of the neutralized medium of between 5.5 and 7.5, causes significant coloring of the product.

[0010] For the purposes of this invention, "measurement of the pH of a 5% mass dispersion in water" refers to the analytical method for measuring the pH of a dispersion of a composition based on APG according to the provisions of standard NF EN 1262, said measurement is carried out by potentiometric measurement using a combined pH electrode (aqueous media) and a pH meter.

[0011] This coloration can alter the organoleptic qualities of the finished products in which the APG compositions are introduced. Therefore, solutions are being developed to minimize the coloration of compositions containing APGs whose alkyl hydrocarbon chain R has 12 or more carbon atoms. Two known prior art techniques are commonly used to obtain such lightly colored (< 1.5 vcs) APG-based compositions with an alkyl hydrocarbon chain R having 12 or more carbon atoms.

[0012] For the purposes of this invention, "low-color composition" means a composition whose Gardner color index, as defined by DIN-ISO 4630, is less than or equal to 1.5 VCS. The Gardner color index is measured using a LICO 200 / Dr. LANGE colorimeter (or equivalent) that performs measurements by light transmission on any medium. Such a colorimeter operates with a halogen lamp corresponding to the standard illuminant C, as defined by DIN 5033, and with a standard observer having a 2° field of view. During the measurement, a reference beam compensates for variations in the recorded values ​​due to differences in lamp and temperature.

[0013] The first approach involves adding a reducing agent to the base being used. Examples of such reducing agents include sodium borohydride (NaBH4) and sodium hypophosphite (NaH2PO2). This solution is not entirely satisfactory. While very effective at minimizing discoloration of the treated composition, NaBH4 is a dangerous reducing agent to handle and use (corrosive product, releases hydrogen). NaH2PO2, on the other hand, is very ineffective even at high concentrations.

[0014] The second commonly used and previously described method for minimizing the color of APG-based compositions, whose alkyl hydrocarbon chain R has 12 or more carbon atoms, is decolorization with hydrogen peroxide (H₂O₂) during the finishing step. While effective, this step is nonetheless time-consuming because it requires adjusting the pH of a 5% wt% dispersion in water to between 7.0 and 7.5 while maintaining the oxidizing power of the medium through the addition of H₂O₂. This delicate step can take several hours and thus significantly increase production time, thereby reducing productivity.

[0015] Other prior art documents disclose additional preparation methods. For example, EP0092876A1 describes a transglycosylation preparation including a neutralization step carried out with Na2CO3. US5681938A describes a process for preparing APG including a realization step carried out with a tertiary amine. US5576425A discloses a neutralization step including carbonates with MgO as the preferred base. Finally, WO98 / 35975A1 describes an APG preparation including the use of a binary sulfate catalyst, itself a mixture of H2SO4 and an inorganic base including carbonates.

[0016] The technical problem to be solved is therefore to find an alternative to the neutralization of APG compositions whose hydrocarbon alkyl chain R has a number of carbon atoms greater than or equal to 12. This alternative must be effective and easy to implement, while guaranteeing a color less than or equal to 1.5 vcs without implementing a bleaching step.

[0017] A solution of the present invention is a process for preparing a color composition (C) of less than or equal to 1.5 cvs comprising, by 100% of its mass: (i) an amount greater than or equal to 40% by mass and less than or equal to 95% by mass, preferably greater than or equal to 50% by mass and less than or equal to 95% by mass, even more preferably greater than or equal to 70% by mass and less than or equal to 90% by mass of an alcohol of formula (I): R-OH (I), in which R represents a hydrocarbon radical, linear or branched, saturated or unsaturated, which may include at least one hydroxy function, and which comprises from twelve to twenty-two carbon atoms, or of a mixture of alcohols of formula (I);(ii) an amount greater than or equal to 5% by mass and less than or equal to 60% by mass, preferably greater than or equal to 5% by mass and less than or equal to 50% by mass, and even more preferably greater than or equal to 10% by mass and less than or equal to 30% by mass of a composition (C1) represented by the formula (II): RO-(G)xH (II), in which the remainder G represents the remainder of a reducing sugar, R represents a radical as defined in formula (I) and x, which indicates the average degree of polymerization of the remainder G, represents a decimal number greater than 1.05 and less than or equal to 2.5, or of a mixture of compositions (C1) of formula (II); it being understood that the sum of the mass proportions of compounds of formulas (I) and (II) in composition (C) is equal to 100% by mass, said process comprising successively: a) A glycosylation step, consisting of a reaction between at least one alcohol of formula (I) and at least one reducing sugar of formula (III): HO-(G)-H (III), in the presence of at least one acid catalyst (AC), at a temperature greater than or equal to 100°C and less than or equal to 120°C, preferably greater than or equal to 100°C and less than or equal to 115°C, even more preferably greater than or equal to 100°C and less than or equal to 110°C, the acid catalyst (AC) being selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, hypophosphorous acid, methanesulfonic acid, para-toluenesulfonic acid, trifluoromethanesulfonic acid, and acid ion-exchange resins; b) A pre-neutralization step of the reaction medium obtained from step a),Pre-neutralization being carried out so as to obtain a reaction medium of which a 5% mass dispersion of said reaction medium in water has a pH value between 3.5 and 5.5, c) A step c) of removing the reducing sugar of formula (III), which did not react in step a), from the pre-neutralized reaction medium obtained in step b), d) A step d) of neutralizing the reaction medium from step c) with an aqueous solution comprising a basic agent (Ab) chosen from the elements of the group consisting of: ▪ carbonates of formula (IVa): XnCO3 (IVa), in which X represents a sodium or potassium atom and n is an integer equal to 2, or X represents a calcium or magnesium atom and n is an integer equal to 1, or ▪ hydrogen carbonates of formula (IVb): Y(HCO3)m (IVb), in which Y represents an atom of sodium or potassium and m is an integer equal to 1,or Y represents a calcium atom or a magnesium atom and m is an integer equal to 2, the naturalization being carried out in such a way as to obtain a reaction medium of which a 5% mass dispersion of said reaction medium in water has a pH value between 5.5 and 7.5, and e) A step e) of recovery of at least one color composition (C) less than or equal to 1.5 vcs. ,

[0018] The color index characterizing the composition (C) prepared according to the process of the present invention is the Gardner color index, as defined by DIN-ISO 463. The Gardner color index is measured using a LICO 200 / Dr. LANGE colorimeter (or equivalent) that performs measurements by light transmission on any medium. Such a colorimeter operates with a halogen lamp corresponding to the standard illuminant C, defined by DIN 5033, and with a standard observer having a 2° field of view. During the measurement, a reference beam compensates for variations in the recorded values ​​due to differences in lamp and temperature.

[0019] The unit of expression of the Gardner color index, characterizing the composition (C) prepared according to the process which is the subject of the present invention, is the VCS.

[0020] Depending on the case, the process according to the invention may have one or more of the following characteristics: said composition (C1) consists of a mixture of compounds represented by the formulas (II1), (II2), (II3), (II4) and (II5): RO-(G)1-H (II1), RO-(G)2-H (II2), RO-(G)3-H (II3), RO-(G)4-H (II4), RO-(G)5-H (II5), in the respective molar proportions a1, a2, a3, a4 and a5, such that: ▪ the sum: a1+ a2 + a3 + a4 + a5 is equal to 1, and ▪ the sum a1 + 2a2 + 3a3 + 4a4 + 5a5 is equal to x; composition (C) comprises an amount less than or equal to 2% by mass, more particularly less than or equal to 1% by mass of the reducing sugar of formula (III): HO-(G)-H (III); it being understood that the sum of the mass proportions of the compounds of formulas (I), (II) and (III) in composition (C) is equal to 100% by mass;the basic agent (Ab) included in the aqueous solution used in step d) of neutralization is chosen from sodium carbonate (Na 2 CO 3 ) or sodium hydrogen carbonate (NaHCO 3 ); step b) of pre-neutralization is carried out with at least one of the following compounds: sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH 4 OH), monoethanolamine, diethanolamine, triethanolamine and triethylamine; step b) of pre-neutralization is carried out with one of the following compounds: sodium carbonate (Na 2 CO 3 ), sodium hydrogen carbonate (NaHCO 3 ), and calcium carbonate (CaCO 3 ); the reducing sugar of formula (III) chosen for the glycolysation of step a) is chosen from the elements of the group consisting of glucose, xylose, arabinose, rhamnose; step c) of removing the reducing sugar of formula (III) is carried out by filtration, centrifugation or decantation;in step d) the aqueous solution of basic agent (Ab) comprises between 10% and 25% by mass of said basic agent (Ab); step a) comprises the following successive substeps: i) Introduction of an alcohol of formula (I) or a mixture of alcohols of formula (I), into a reactor (Re) equipped with mechanical stirring and a vacuum device; ii) Heating of the alcohol of formula (I) to a temperature between 80°C and 90°C under mechanical stirring; iii) Loading of the reducing sugar of formula (III) into the reactor (Re); iv) Introduction of the acid catalyst (CA) into the reactor (Re), v) Heating under partial vacuum of the reaction medium from substep iv) and present in the reactor (Re) to a temperature between 100°C and 110°C during the duration of the reaction, and vi) Cooling of the reaction medium from substep v) to a temperature between 70°C and 80°C;the radical R is chosen from the following radicals: lauryl (or n-dodecyl), myristyle (or n-tetradecyl), n-pentadecyl, cetyl (or n-hexadecyl), n-heptadecyl, stearyl (or n-octadecyl), palmitoleyl (or 9-hexadecenyl), oleyl (or 9-octadecenyl), linoleyl (9,12-octadecadienyl), linolenyl (or 6,9,12-octadecatrienyl), nonadecyl, arachidyl (or n-eicosyl), behenyl (or n-docosyl), erucyl (13-docosenyl), or 12-hydroxystearyl; the radical R is chosen from the following radicals: 2-hexyl octyl, 2-hexyl decyl, 2-hexyl dodecyl, 2-octyl decyl, 2-octyl dodecyl, 2-decyl tetradecyl, isostearyl (or 16-methyl heptadecyl) or isomyristyle (or 13-methyl tridecyl);The acid catalyst (AC) is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, hypophosphorous acid, methanesulfonic acid, para-toluenesulfonic acid, trifluoromethanesulfonic acid, and acid ion exchange resins; during substeps ii) to iv) the reactor (Re) is inert under nitrogen; the process includes, between substeps ii) and iii) a vacuum step, preferably at a pressure less than or equal to 50 millibars; substep vi) is carried out at atmospheric pressure.

[0021] The use of carbonates of formula (IVa) or hydrogen carbonates of formula (IVb) does not increase the color of composition (C) (the presence of a reducing agent is therefore unnecessary) while neutralizing a 5% wt% dispersion of composition (C) (with a pH between 5.5 and 7.5) to the desired pH. The use of a basic agent (Ab) avoids a decolorization step involving a peroxide or other agent, as it allows a color of 1.5 vcs or less to be achieved.

[0022] By reducing sugar, we mean in the definition of formula (II) and in the definition of formula (III), the saccharide derivatives which do not have in their structures a glycosidic bond established between an anomeric carbon and the oxygen of an acetal group as defined in the reference work: "Biochemistry", Daniel Voet / Judith G. Voet, p. 250, John Wyley & Sons, 1990.

[0023] The oligomeric structure (G)x present in formula (II) can appear in all forms of isomerism, whether optical isomerism, geometric isomerism or positional isomerism; it can also represent a mixture of isomers.

[0024] In formula (II) as defined above, the radical R is linked to G by the anomeric carbon of the saccharide remainder, so as to form an acetal function.

[0025] According to a particular aspect of the present invention, in the definition of compounds of formula (II) and formula (III), G represents the remainder of a reducing sugar selected from glucose, dextrose, sucrose, fructose, idose, gulose, galactose, maltose, isomaltose, maltotriose, lactose, cellobiose, mannose, ribose, xylose, arabinose, lyxose, allose, altrose, rhamnose, dextran or tallose.

[0026] According to a particular aspect of the present invention, in the definition of compounds of formula (II), G represents the remainder of a reducing sugar selected from the remainders of glucose, xylose, arabinose or rhamnose, and x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.5.

[0027] According to a further particular aspect of the present invention, in the definition of compounds of formula (II), G represents the remainder of a reducing sugar chosen from the remainders of glucose, xylose, arabinose or rhamnose, and x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, and even more particularly greater than or equal to 1.25 and less than or equal to 2.0.

[0028] According to another particular aspect of the present invention, the reducing sugar of formula (III) is selected from the elements of the group consisting of glucose, dextrose, sucrose, fructose, idose, gulose, galactose, maltose, isomaltose, maltotriose, lactose, cellobiose, mannose, ribose, xylose, arabinose, lyxose, allose, altrose, rhamnose, dextran or tallose.

[0029] According to a more particular aspect of the present invention, the reducing sugar of formula (III) is chosen from glucose, xylose, arabinose or rhamnose.

[0030] The process according to the invention consists of pre-neutralizing the medium at the end of the glycosylation reaction to achieve a pH value of between 3.5 and 5.5 for a 5% mass dispersion of said medium in water. This pre-neutralization can be achieved with an alkali metal or alkaline earth metal carbonate, an alkali metal or alkaline earth metal hydrogen carbonate, or any other base known to those skilled in the art. The residual reducing sugar of formula (III) is then removed by filtration, and an aqueous solution of a basic agent (Ab) is added to achieve a pH value of between 5.5 and 7.5 for the 5% mass dispersion of composition (C) in water.

[0031] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 45% to 55% mass of a mixture (M1) of alcohols of formula (I) comprising, for 100% of the mass of said mixture (M1), 50% mass of an alcohol of formula (I) in which R represents the n-hexadecyl radical and 50% mass of an alcohol of formula (I) in which R represents the n-octadecyl radical of 45% to 54% mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-hexadecyl radical and the n-octadecyl radical less than 1% mass of glucose.

[0032] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 45% to 55% mass of a mixture (M'1) of alcohols of formula (I) comprising, for 100% of the mass of said mixture (M'1), 70% mass of an alcohol of formula (I) in which R represents the n-hexadecyl radical and 30% mass of an alcohol of formula (I) in which R represents the n-octadecyl radical, 45% to 54% mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the suppression of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-hexadecyl radical and the n-octadecyl radical less than 1% mass of glucose.

[0033] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: of 75% to 90% by mass of a mixture (M"1) of alcohols of formula (I) comprising for 100% of the mass of said mixture (M"1), 50% by mass of an alcohol of formula (I) in which R represents the n-hexadecyl radical and 50% by mass of an alcohol of formula (I) in which R represents the n-octadecyl radical of 10% to 24% by mass of at least one composition (C1) represented by the formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the suppression of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-hexadecyl radical and the n-octadecyl radical less than 1% by mass of glucose.

[0034] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: of 75% to 90% by mass of a mixture (M'"1) of alcohols of formula (I) comprising for 100% of the mass of said mixture (M‴1), 70% by mass of an alcohol of formula (I) in which R represents the n-hexadecyl radical and 30% by mass of an alcohol of formula (I) in which R represents the n-octadecyl radical of 10% to 24% by mass of at least one composition (C1) represented by the formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the suppression of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-hexadecyl radical and the n-octadecyl radical less than 1% by mass of glucose.

[0035] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 75% to 90% by mass of an alcohol of formula (I) in which R represents the n-tetradecyl radical; 10% to 24% by mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-tetradecyl radical; less than 1% by mass of glucose.

[0036] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 75% to 90% by mass of a mixture of alcohols of formula (I) in which R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical and the n-octadecyl radical; 10% to 24% by mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical, and the n-octadecyl radical; less than 1% by mass of glucose.

[0037] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 75% to 90% by mass of a mixture of alcohols of formula (I) in which R represents the n-eicosyl radical and the n-docosyl radical; 10% to 24% by mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-eicosyl radical and the n-docosyl radical; less than 1% by mass of glucose.

[0038] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 75% to 90% by mass of a mixture of alcohols of formula (I) in which R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical, the n-eicosyl radical and the n-docosyl radical; 10% to 24% by mass of at least one composition (C1) represented by formula (II) in which G represents the glucosyl or α,β-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-glucopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical, the n-eicosyl radical and the n-docosyl radical; less than 1% by mass of glucose.

[0039] According to one particular aspect, the process is for the preparation of a color composition (C) of less than or equal to 1.5 VCS, comprising 100% of its mass: 70% to 90% by mass of a mixture of alcohols of formula (I) in which R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical, the n-eicosyl radical and the n-docosyl radical; 10% to 29% by mass of at least one composition (C1) represented by formula (II) in which G represents the xylosyl or α,β-D-xylopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of α,β-D-xylopyranose, x represents a decimal number greater than or equal to 1.05 and less than or equal to 2.0, R represents the 2-octyldodecyl radical; less than 1% by mass of xylose.

[0040] According to one particular aspect, the basic agent (Ab) present in the aqueous solution is potassium carbonate of formula (IVa) in which X represents the potassium atom and n is equal to 2.

[0041] According to one particular aspect, the basic agent (Ab) present in the aqueous solution is sodium hydrogen carbonate of formula (IVb) in which Y represents a sodium atom and m is equal to 1.

[0042] According to a particular aspect, the acid catalyst (AC) is chosen from the elements of the group consisting of sulfuric acid, phosphoric acid, hypophosphorous acid, methanesulfonic acid, p-toluenesulfonic acid. EXAMPLES

[0043] Comparison of the effect of the neutralizing agent on the color of a composition of fatty alcohols and alkyl polyglucosides when the basic neutralizing agent used is a carbonate according to the invention or sodium hydroxide (comparative neutralizing agent).

[0044] Comparisons between a carbonate and soda as a neutralizing agent were carried out. For this, glycosylation reactions were carried out from crystallized glucose and various fatty alcohols in the form of cuts or pure: cetearyl C-16 / 18 cut, arachidyl / behenic C-20 / 22 cut, tetradecanol-1 (C-14 alcohol) and dodecanol-1 (C-12 alcohol). 1. Examples according to the invention Example 1.1 (Alcohol blend 16 / 18 and Na₂CO₃ as pre-neutralizing and neutralizing agents) according to the invention STEP 1: Glycosylation Reaction:

[0045] 967.4 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then placed under vacuum at pressures below 50 Torrs. Anhydrous glucose powder is added to achieve a molar ratio of 6:1 between fatty alcohols and glucose. The mixture is then inert with nitrogen. To initiate the etherification reaction, 0.9 g of a 50% aqueous H₃PO₂ solution is added, followed by 1.1 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours and 45 minutes. STEP 2: Neutralization of the reaction medium:

[0046] The medium is then cooled to 80°C at atmospheric pressure and pre-neutralized by adding 2.21 g of a 25% aqueous Na₂CO₃ solution. The product is then transferred to a glass flask and incubated at 80°C for 5 hours to allow residual glucose to settle. The product (upper phase) is then filtered through filter paper (approximately 10 µm). A 5% wt. dispersion in water shows a pH of 4.7 and a color of 0.6 VCS. The product is then neutralized by adding 4.61 g of a 25% aqueous Na₂CO₃ solution. The product is then transferred to a glass flask and incubated at 80°C for 24 hours to allow residual glucose to settle. The product (upper phase) is collected and labeled (Composition 1). Analysis:

[0047] The pH value of a 5% mass dispersion in water of Composition 1 is 6.8, and the color measurement of Composition 1 is 0.5 VCS. Example 1.2 (Alcohol blend 16 / 18 and NaOH as a pre-neutralizing agent and Na2CO3 as a neutralizing agent) according to the invention STEP 1: Glycosylation Reaction:

[0048] 1364.8 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then evacuated to pressures below 50 Torrs. 179.2 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 1.2 g of a 50% aqueous H₃PO₂ solution are added, followed by 1.6 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours and 45 minutes. STEP 2: Neutralization of the reaction medium:

[0049] The medium is cooled to 80°C at atmospheric pressure and then pre-neutralized by introducing 3.4 g of a 25% aqueous NaOH solution with stirring. The product is then transferred to a glass flask and placed in an oven at 80°C for 5 hours to allow residual glucose to settle. The product (upper phase) is then filtered through filter paper (~< 10 µm). A 5% wt. dispersion in water shows a pH of 4.5 and a color of 1.0 VCS. The product (880 g) is then neutralized at 85°C in a reactor with stirring by introducing 3.57 g of a 10% aqueous Na₂CO₃ solution. The product is collected and labeled (Composition 2). Analysis:

[0050] The pH value of a 5% mass dispersion in water of Composition 2 is 7.2, and the color measurement of Composition 2 is 0.9 VCS. Example 1.3 (Alcohol blend 16 / 18 and NaOH as a pre-neutralizing agent and NaHCO3 as a neutralizing agent) according to the invention STEP 1: Glycosylation Reaction:

[0051] 271.1 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then evacuated to pressures below 50 Torrs. 35.7 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.2 g of a 50% aqueous H₃PO₂ solution are added, followed by 0.3 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours and 45 minutes. STEP 2: Neutralization of the reaction medium:

[0052] The mixture is cooled to 85°C at atmospheric pressure and then pre-neutralized by adding 0.4 g of a 25% aqueous NaOH solution with stirring. The product is then transferred to a glass flask and placed in an oven at 80°C for 24 hours to allow residual glucose to settle. A 5% wt. dispersion in water shows a pH of 3.5 and a color of 0.5 VCS. The product (173.8 g) is then neutralized in a reactor at 85°C with stirring by adding 1.9 g of an 8% aqueous NaHCO3 solution. The product is collected and labeled (Composition 3). Analysis:

[0053] The pH value of a 5% mass dispersion in water of Composition 3 is 6.3, and the color measurement of Composition 3 is 0.4 VCS. Example 1.4 (Alcohol blend 20 / 22 and NaOH as a pre-neutralizing agent and Na2CO3 as a neutralizing agent) according to the invention STEP 1: Glycosylation Reaction:

[0054] 284.7 g of benethyl / arachidyl alcohols (C-20 / 22) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then evacuated to pressures below 50 Torrs. 29.2 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.3 g of a 50% aqueous H₃PO₂ solution is added, followed by 0.4 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 4.5 hours. STEP 2: Neutralization of the reaction medium:

[0055] The medium is cooled to 90°C at atmospheric pressure and then pre-neutralized by adding 0.89 g of a 25% aqueous NaOH solution while stirring. The product is then transferred to a glass flask and placed in an oven at 80°C for 24 hours to allow residual glucose to settle. A 5% wt. dispersion in water shows a pH of 5.1 and a color of 0.3 VCS.

[0056] 175.4 g of product (upper phase) is then neutralized at 90°C in a stirred reactor, by introducing 0.61 g of a 10% aqueous Na2CO3 solution.

[0057] The product is recovered and referenced (Composition 4). Analysis:

[0058] The pH value of a 5% mass dispersion in water of Composition 4 is 6.8, and the color measurement of Composition 4 is 0.5 VCS. Example 1.5 (Alcohol blend 20 / 22 and Na2CO3 as a pre-neutralizing agent and Na2CO3 as a neutralizing agent) according to the invention STEP 1: Glycosylation Reaction:

[0059] 391.9 g of benethyl / arachidyl alcohol (C-20 / 22) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then evacuated to pressures below 50 Torrs. 40.1 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.4 g of a 50% aqueous H₃PO₂ solution is added, followed by 0.6 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 4.5 hours. STEP 2: Neutralization of the reaction medium:

[0060] The mixture is cooled to 90°C at atmospheric pressure and then pre-neutralized by introducing 2.1 g of a 25% aqueous Na₂CO₃ solution with stirring. The product is then transferred to a glass flask and placed in an oven at 105°C for 24 hours to allow residual glucose to settle. A 5% wt. dispersion in water shows a pH of 5.2 and a color of 0.7 VCS. The product (266 g) is then neutralized at 90°C in a reactor with stirring by introducing 0.1 g of a 25% aqueous Na₂CO₃ solution.

[0061] The product is recovered and referenced (Composition 5). Analysis:

[0062] The pH value of a 5% mass dispersion in water of Composition 5 is 6.5, and the color measurement of Composition 5 is 0.7 VCS. Example 1.6 (tetradecanol-1 and Na₂CO₃ as pre-neutralizing agents and Na₂CO₃ as neutralizing agents) according to the invention STEP 1: Glycosylation Reaction:

[0063] 428.7 g of C-14 myristyl alcohol (or tetradecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 80°C and stirred and bubbling with nitrogen. The mixture is then placed under vacuum at 35 Torrs. 59.9 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 1.0 g of a 50% aqueous H₃PO₂ solution is added, followed by 0.7 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours. STEP 2: Neutralization of the reaction medium:

[0064] The mixture is cooled to 70°C at atmospheric pressure and then pre-neutralized by adding 1.6 g of a 25% aqueous NaOH solution with stirring. The product is then transferred to a glass flask and placed in an oven at 80°C for 24 hours to allow residual glucose to settle. A 5% wt. dispersion in water shows a pH of 5.2 and a color of 0.6 VCS. The product (337 g) is then neutralized at 70°C in a reactor with stirring by adding 0.7 g of a 10% aqueous Na₂CO₃ solution. The product is collected and labeled (Composition 6). Analysis:

[0065] The pH value of a 5% mass dispersion in water of Composition 6 is 7.3, and the color measurement of Composition 6 is 0.7 VCS. Example 1.7 (dodecanol-1 and Na2CO3 as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention STEP 1: Glycosylation Reaction:

[0066] 414.5 g of lauryl alcohol (C-12) (or dodecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then placed under vacuum at 30 Torrs. 57.9 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.4 g of a 50% aqueous H3PO2 solution followed by 0.7 g of a 98% aqueous H2SO4 solution are added, and the temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours. STEP 2: Neutralization of the reaction medium:

[0067] The mixture is then cooled to 67°C at atmospheric pressure and pre-neutralized by introducing 3.55 g of a 10% aqueous Na₂CO₃ solution. The product is filtered through a plate filter (~< 100 µm) to remove residual glucose. A 5% wt. dispersion in water shows a pH of 3.7 and a color of 1.1 VCS. The product (197 g) is then neutralized in a reactor at 67°C by introducing 2.97 g of a 10% aqueous Na₂CO₃ solution with stirring.

[0068] The product is recovered and referenced (Composition 7). Analysis:

[0069] The pH value of a 5% mass dispersion in water of Composition 7 is 6.1, and the color measurement of Composition 6 is 1.5 VCS. 2. Comparative examples Example 2.1: Comparative example (16 / 18 alcohol blend and NaOH as pre-neutralizing agent and NaOH as neutralizing agent) STEP 1: Glycosylation Reaction:

[0070] 778.1 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then evacuated to pressures below 50 Torrs. 102.2 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.7 g of a 50% aqueous H₃PO₂ solution is added, followed by 0.9 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours and 45 minutes. STEP 2: Neutralization of the reaction medium:

[0071] The mixture is then cooled to 80°C at atmospheric pressure and pre-neutralized by adding 1.86 g of a 25% aqueous NaOH solution. The product is then transferred to a glass flask and incubated at 80°C for 3 hours to allow residual glucose to settle. A 5% wt. dispersion in water yields a pH of 3.3 and a color of 0.6 VCS.

[0072] The product is then neutralized at 80°C by introducing 0.28 g of a 25% aqueous NaOH solution. The product is recovered and recorded (Composition 1'). Analysis:

[0073] The pH value of a 5% mass dispersion in water of Composition 1' is 6.2, and the color measurement of Composition 1' is 3.8 VCS. Example 2.2: comparative example (C-12 alcohol and NaOH as pre-neutralizing agent and NaOH as neutralizing agent) STEP 1: Glycosylation Reaction:

[0074] 190.6 g of lauryl alcohol (C-12) (or dodecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation apparatus. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The mixture is then placed under vacuum at 30 Torrs. 26.6 g of anhydrous glucose powder are added. The mixture is inert under nitrogen. To initiate the etherification reaction, 0.2 g of a 50% aqueous H₃PO₂ solution are added, followed by 0.3 g of a 98% aqueous H₂SO₄ solution. The temperature is increased and maintained at 105°C. The reaction is carried out for 5 hours. STEP 2: Neutralization of the reaction medium:

[0075] The mixture is then cooled to 75°C at atmospheric pressure and pre-neutralized by introducing 0.70 g of a 25% aqueous NaOH solution with stirring. A 5% wt. dispersion in water shows a pH of 5.6 and a color of 2.0 VCS. The product is filtered through a K200 filter (~< 3-6 µm) to remove residual glucose. The product (78 g) is then neutralized in a reactor at 80°C by introducing 0.08 g of a 25% aqueous NaOH solution with stirring.

[0076] The product is retrieved and referenced (Composition 2'). Analysis:

[0077] The pH value of a 5% mass dispersion in water of Composition 2' is 6.5, and the color measurement of Composition 2' is 4.5 VCS. 3. Observation and analysis of results

[0078] Table 1 below summarizes the results of the process for preparing compositions (C) obtained by the reaction between glucose and C-16 / 18 alcohols (a mixture of 1-hexadecanol and 1-octadecanol). The different parameters studied are: i) the nature of the pre-neutralizing agent (Na2CO3 or NaOH) and ii) the nature of the final neutralizing agent (Na2CO3, NaHCO3 or NaOH).

[0079] The compositions referenced "Composition 1", "Composition 2" and "Composition 3" are obtained by implementing a process according to the invention, and the composition referenced "Composition 1" is obtained by implementing a comparative process of the prior art. Table 1 Reference Composition 1' Composition 1 Composition 2 Composition 3 Pre-neutralizing agent NaOH Na2CO3 NaOH NaOH Neutralizing Agent NaOH Na2CO3 Na2CO3 NaHCO3 pH dispersion 5% in water 6,2 6,8 7,2 6,3 Color (vcs) 3,8 0,5 0,9 0,4

[0080] These tests demonstrate that the presence of a pre-neutralization step with an aqueous NaOH solution and a neutralization step with an aqueous NaOH solution results in an excessively high color intensity in the resulting composition (up to 3.8 VCS for Composition 1'). In comparison, when the pre-neutralization step is performed with a NaOH solution (Composition 2) or a Na₂CO₃ solution (Composition 1), and the neutralization step is performed with an aqueous Na₂CO₃ solution, the colors of the resulting compositions are very low (< 1 VCS).

[0081] For the preparation of Composition 3, the process according to the invention was implemented by carrying out a pre-neutralization step with an aqueous solution of NaOH (to reach a pH between 3.5 and 5.5), then a neutralization step with a NaHCO3 solution after filtration (to reach a pH between 5.5 and 7.5).

[0082] This test highlights that it is possible to use sodium hydrogen carbonate during the neutralization step of the process according to the invention to guarantee a low color of the desired compositions (since the final color obtained is 0.4 vcs for Composition 3).

[0083] Table 2 presents results of the process for preparing compositions (C) obtained by the reaction between glucose and C-20 / 22 alcohols (mixture of 1-eicosanol and 1-docosanol), between glucose and C14 alcohol (or 1-tetradecanol), between glucose and C12 alcohol (or 1-dodecanol), by studying the same parameters as those involved in the study above. Table 2 Reference Composition 4 Composition 5 Composition 6 Composition 2' Composition 7 Alkyl Polyglucoside Chain C-20 / 22 C-14 C-12 Pre-neutralizer NaOH Na2CO3 NaOH NaOH Na2CO3 Neutralizer Na2CO3 Na2CO3 Na2CO3 NaOH Na2CO3 pH dispersion 5% in water 6,8 6,5 7,3 6,5 6,1 Color (vcs) 0,5 0,7 0,7 4,5 1,5

[0084] The process according to the invention makes it possible to obtain a composition (C), with low colour (less than or equal to 1.5 VCS), prepared by the reaction of glucose and fatty alcohols comprising 12, 14, 20 and 22 carbon atoms.

[0085] On the other hand, by implementing a process for preparing Composition 2' (reaction between glucose and 1-dodecanol) using sodium hydroxide for both the pre-neutralization and neutralization steps, the analytical results obtained show that the color value of the final mixture is 4.5 VCS, which is significantly higher than 1.5 VCS.

[0086] In conclusion, the process according to the invention makes it possible to obtain compositions comprising fatty alcohols and alkylpolyglycosides with low colour (colour less than or equal to 1.5 VCS), from the reaction of at least one reducing sugar with a fatty alcohol comprising 12 to 22 carbon atoms.

Claims

1. A Process for the preparation of a composition (C) having a colour lower than or equal to 1.5 vcs, comprising, for 100% of its mass: i) a quantity greater than or equal to 40% by mass and less than or equal to 95% by mass of an alcohol of formula (I):         R-OH     (I), in which R represents a hydrocarbon radical, linear or branched, saturated or unsaturated, possibly comprising at least one hydroxyl function, and comprising twelve to twenty-two carbon atoms, or a mixture of alcohols of formula (I); ii) a quantity greater than or equal to 5% by mass and less than or equal to 60% by mass of a composition (C1) represented by formula (II):         R-O-(G)x-H     (II), in which the residue G represents the residue of a reducing sugar, R represents a radical as defined in formula (I) and x, which indicates the average degree of polymerization of the residue G, represents a decimal number greater than or equal to 1.05 and less than or equal to 2.5, or a mixture of compositions (C1) of formula (II); it being understood that the sum of the mass proportions of the compounds of formulae (I) and (II) in the composition (C) is equal to 100% by mass, said process successively comprising: a) A glycosylation step a), consisting of a reaction between at least one alcohol of formula (I) and at least one reducing sugar of formula (III): H-O-(G)-H (III), in the presence of at least one acid catalyst (CA), at a temperature greater than or equal to 100°C and less than or equal to 120°C, the at least one acid catalyst (CA) being chosen from the elements of the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, hypophosphorous acid, methane-sulfonic acid, para-toluene sulfonic acid, trifluoromethane sulfonic acid and ion exchange resins, b) A pre-neutralization step b) of the reaction medium resulting from step a), the pre-neutralization being carried out so as to obtain a reaction medium, a 5% by mass dispersion of which in water exhibits a pH value comprised between 3.5 and 5.5, c) A step c) of eliminating the reducing sugar of formula (III), which has not reacted in step a), from the pre-neutralized reaction medium obtained in step b), d) A neutralization step d) of the reaction medium resulting from step c) with an aqueous solution comprising a basic agent (Ab) chosen from the elements of the group consisting of: - carbonates of formula (IVa):         XnCO3     (IVa), wherein X represents a sodium or potassium atom and n is an integer equal to 2, or X represents a calcium atom or a magnesium atom and n is an integer equal to 1, or - hydrogencarbonates of formula (IVb):         Y(HCO3)m     (IVb), wherein Y represents a sodium or potassium atom and m is an integer equal to 1, or Y represents a calcium atom or a magnesium atom and m is an integer equal to 2, the neutralization being carried out so as to obtain a reaction medium, a 5% by mass dispersion of which in water exhibits a pH value comprised between 5.5 and 7.5, and e) A step e) of recovering at least one composition (C) having a colour lower than or equal to 1.5 vcs.

2. The Process according to claim 1, characterized in that said composition (C1) consists of a mixture of compounds represented by the formulae (III), (II2), (113), (II4) and (II5):         R-O-(G)1-H     (II1),         R-O-(G)2-H     (II2),         R-O-(G)3-H     (II3),         R-O-(G)4-H     (II4),         R-O-(G)5-H     (II5), in the respective molar proportions a1, a2, a3, a4 and a5, such that: - the sum: a1+ a2 + a3 + a4 + a5 is equal to 1, and - the sum a1 + 2a2 + 3a3 + 4a4 + 5a5 is equal to x.

3. The Process according to any one of claims 1 or 2, characterized in that the composition (C) comprises a quantity less than or equal to 2% by mass, more particularly less than or equal to 1% by mass of the reducing sugar of formula (III):         H-O-(G)-H     (III); it being understood that the sum of the mass proportions of the compounds of formulae (I), (II) and (III) in the composition (C) is equal to 100% by mass.

4. The Process according to any one of claims 1 to 3, characterized in that the basic agent (Ab) comprised in the aqueous solution used in neutralization step d) is chosen from sodium carbonate (Na2CO3) or sodium hydrogencarbonate (NaHCO3).

5. The Process according to any one of claims 1 to 4, characterized in that the pre-neutralization step b) is carried out with at least one of the following compounds: sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH), monoethanolamine, diethanolamine, triethanolamine and triethylamine.

6. The Process according to any one of claims 1 to 5, characterized in that the pre-neutralization step b) is carried out with one of the following compounds: sodium carbonate (Na2CO3), sodium hydrogencarbonate (NaHCO3), and calcium carbonate (CaCO3).

7. The Process according to any one of claims 1 to 6, characterized in that the reducing sugar of formula (III) chosen for the glycosylation of step a) is chosen from the elements of the group consisting of glucose, xylose, arabinose, rhamnose.

8. The Process according to any one of claims 1 to 7, characterized in that step c) of eliminating the reducing sugar of formula (III) is carried out by filtration, centrifugation or decantation.

9. The Process according to any one of claims 1 to 8, characterized in that in step d) the aqueous solution of basic agent (Ab) comprises between 10% and 25% by mass of said basic agent (Ab).

10. The Process according to any one of claims 1 to 9, characterized in that step a) comprises the following successive sub-steps: i) Introduction of an alcohol of formula (I) or a mixture of alcohols of formula (I), into a reactor (Ré) equipped with mechanical stirring and a vacuum distillation device; ii) Heating the alcohol of formula (I) to a temperature comprised between 80°C and 90°C under mechanical stirring; iii) Charging the reducing sugar of formula (III) into the reactor (Ré); iv) Introduction of the acid catalyst (CA) into the reactor (Ré), v) Heating under partial vacuum of the reaction medium resulting from sub-step iv) and present in the reactor (Ré) at a temperature comprised between 100°C and 110°C during the duration of the reaction, and vi) Cooling the reaction medium resulting from sub-step v) to a temperature comprised between 70°C and 80°C.

11. The Process according to claim 10, characterized in that the radical R is chosen from the following radicals: lauryl (or n-dodecyl), myristyl (or n-tetradecyl), n-pentadecyl, cetyl (or n-hexadecyl), n-heptadecyl, stearyl (or n-octadecyl), palmitoleyl (or 9-hexadecenyl), oleyl (or 9-octadecenyl), linoleyl (9,12-octadecadienyl), linolenyl (or 6,9,12-octadecatrienyl) nonadecyl, arachidyl (or n-eicosyl), behenyl (or n-docosyl), erucyl (13-docosenyl), or 12-hydroxystearyl.

12. The Process according to claim 10, characterized in that the radical R is chosen from the following radicals: 2-hexyl octyl, 2-hexyl decyl, 2-hexyl dodecyl, 2-octyl decyl, 2-octyl dodecyl, 2-decyl tetradecyl, isostearyl (or 16-methyl heptadecyl) or isomyristyl (or 13-methyl tridecyl).

13. The Process according to any one of claims 10 to 12, characterized in that during sub-steps ii) to iv) the reactor (Ré) is purged under nitrogen.

14. The Process according to any one of claims 10 to 13, characterized in that it comprises between sub-steps ii) and iii) a vacuum application step, preferably at a pressure less than or equal to 50 millibars.

15. The Process according to any one of claims 10 to 14, characterized in that sub-step vi) is carried out at atmospheric pressure.