Process for the preparation of weakly colored alkylpolyglycosides with pre-neutralization of the reaction medium

Abstract

Process for the preparation of alkylpolyglycosides with a color less than or equal to 1.5 vcs comprising successively: A step a) of glycosylation, 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 (CA), at a temperature greater than or equal to 100°C and less than or equal to 120°C, A step b) of pre-neutralization of the reaction medium resulting from step a), A step c) of elimination of the reducing sugar of formula (III), which has not reacted in step a), from the pre-neutralized reaction medium obtained in step b), A step d) of neutralization of the reaction medium resulting from step c) with an aqueous solution comprising a basic agent (Ab), and A step e) of recovery of at least one composition (C) with a color less than or equal to 1.5 vcs.

Description

Title of the invention: Process for the preparation of weakly colored alkylpolyglycosides with pre-neutralization of the reaction medium

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

[0002] AlkylPolyGlycosides or APGs are probably the best examples of bio-sourced 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).

[0004] Their industrial scale manufacturing process is relatively simple and uses as raw materials i) crystallized glucose or xylose or rhamnose 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 sector (hydrogenation of methyl esters from the transesterification of plant 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.

[0005] R-OH (II)

[0006] To carry out this glycolyzation reaction, an acid catalyst of mineral origin or organic is necessary and an excess of alcohols is systematically introduced thus playing the role of reagent and solvent. At the end of the reaction, the APGs are found dispersed or solubilized in the excess alcohol which has not reacted. The APGs are distinguished by the nature and length of the hydrocarbon alkyl chain R, as well as by their average Degree of Polymerization DP, greater than 1 but less than or equal to 2.5.

[0007] At the end of the glycolysation reaction phase, a neutralization step is carried out in order to deactivate the catalyst and stop the reaction.

[0008] Depending on the length of the alkyl chain of the alcohol and the associated use, said alcohol is either removed or retained.

[0009] The neutralization step differs depending on the length of the hydrocarbon alkyl chain. In the case where the latter has a number of carbon atoms less than 12, the neutralization is carried out by an aqueous solution of sodium hydroxide. The excess fatty alcohols present at the end of 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, and the collected APG concentrate is finally solubilized in water. The commercial products thus obtained are therefore in the form of aqueous APG solutions with a mass concentration of between 40 and 80%.

[0010] In the case where the hydrocarbon alkyl chain R has a number of carbon atoms greater than or equal to 12, the neutralization is generally carried out by sodium hydroxide or by potassium hydroxide, alone or in combination with a reducing agent as described in the European patent published under number EP0077167, in the European patent application published under number EP0338151A1, in the European patent EP0388857B1, such as for example sodium borohydride (NaBH4) or sodium hypophosphite (NaH2PO2). The mixture of APG and the excess fatty alcohols is isolated after neutralization and is marketed as such. The proportion of APG and fatty alcohols depends on the molar stoichiometry initially retained for the raw materials and their reactivity. However, proportions of 5 to 30% by mass of APG and 70 to 95% of fatty alcohols are generally observed.The compositions obtained may be in the form of a solid, such as for example in the form of scales or pearls, or in a liquid form, depending on the nature of the alkyl hydrocarbon chain R.

[0011] However, the step of neutralizing APGs whose hydrocarbon alkyl chain R comprises a number of carbon atoms greater than or equal to 12 by a base of the state of the art (example NaOH, KOH), to reach a pH value of a dispersion at 5% by mass in the water of the neutralized medium of between 5.5 and 7.5, causes significant coloring of the product.

[0012] By “measurement of the pH of a 5% mass dispersion in water” is meant in the sense of the present invention 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.

[0013] This coloration can alter the organoleptic qualities of the finished products into which the APG compositions are introduced. This is why solutions are provided to minimize the coloration of compositions containing APGs whose hydrocarbon alkyl chain R comprises a number of carbon atoms greater than or equal to 12. Two levers known from the state of the art are conventionally used to obtain such compositions based on APGs whose hydrocarbon alkyl chain R comprises a number of carbon atoms greater than or equal to 12 that are not very colored (< 1.5 vcs).

[0014] For the purposes of the present invention, the term “low-colored 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) which carries out measurements by light transmission on any medium. Such a colorimeter operates with a halogen lamp corresponding to the standardized illuminant C, defined by DIN 5033 and with a standardized observer having a field of vision of 2°. During the measurement, a reference radiation beam compensates for variations in the recorded values due to differences in lamp and temperature.

[0015] The first lever consists of associating a reducing agent with the base used. Among these reducing agents, we can cite sodium borohydride (NaBH4) or sodium hypophosphite (NaH2PO2). This solution is not entirely satisfactory. Indeed, although very effective in minimizing the coloring of the treated composition, NaBH4 is a reducing agent that is dangerous to handle and implement (corrosive product, release of hydrogen). NaH2PO2 is very ineffective even if it is introduced at a high concentration.

[0016] The second lever commonly used and described in the state of the art, to minimize the color of APG-based compositions, whose hydrocarbon alkyl chain R comprises a number of carbon atoms greater than or equal to 12, is the performance of a bleaching with hydrogen peroxide (H2O2) during the finishing step. Although effective, this step is nevertheless tedious because it requires adjusting the pH value of a 5% mass dispersion in water between 7.0 and 7.5 while maintaining the oxidizing power of the medium by adding H2O2. This delicate step to perform can last several hours and therefore significantly increase the production time, by reducing productivity.

[0017] The technical problem to be solved is therefore to find an alternative to the neutral lization 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.

[0018] A solution of the present invention is a process for preparing a composition (C) of color less than or equal to 1.5 vcs comprising for 100% of its mass:

[0019] 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):

[0020] R-OH (I),

[0021] in which R represents a hydrocarbon radical, linear or branched, saturated or unsaturated, which may comprise at least one hydroxyl function, and comprising from twelve to twenty-two carbon atoms, or a mixture of alcohols of formula (I);

[0022] i. 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% and less than or equal to 30% by mass of a composition (Cl) represented by the formula (II):

[0023] RO-(G)xH (II),

[0024] 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 1.05 and less than or equal to 2.5, or of a mixture of compositions (Cl) of formula (II);

[0025] it being understood that the sum of the mass proportions of the compounds of formulas (I) and (II) in composition (C) is equal to 100% by mass,

[0026] said method successively comprising:

[0027] 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): HO-(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, 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, b. A step b) of pre-neutralization of the reaction medium resulting from step a), c. A step c) of elimination of the reducing sugar of formula (III), which does not have reacted in step a), of the pre-neutralized reaction medium obtained in step b), d. A step d) of neutralization of the reaction medium from step c) with an aqueous solution comprising a basic agent (Ab), e. A step e) of recovery of at least one composition (C) of color less than or equal to 1.5 vcs.

[0028] The color index characterizing the composition (C) prepared according to the process which is the subject of the present invention is the Gardner color index, as defined by the DIN-ISO 463 standard. The Gardner color index is measured using a LICO 200 / Dr LANGE colorimeter (or equivalent) which carries out measurements by light transmission on any medium. Such a colorimeter operates with a halogen lamp corresponding to the standardized illuminant C, defined by the DIN 5033 standard and with a standardized observer with a field of vision of 2°. During the measurement, a reference radiation beam compensates for variations in the recorded values due to differences in lamp and temperature.

[0029] 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.

[0030] Depending on the case, the method according to the invention may have one or more of the following characteristics:

[0031] - said composition (Cl) consists of a mixture of compounds represented by the formulas (III), (112), (113), (114) and (115):

[0032] RO-(G)1-H(II1),

[0033] RO-(G)2-H (112),

[0034] RO-(G)3-H (113),

[0035] RO-(G)4-H (114),

[0036] RO-(G)5-H (115),

[0037] in the respective molar proportions a1, a2, a3, a4 and a5, such that:

[0038] • the sum: al+ a2 + a3 + a4 + a5 is equal to 1, and • the sum al + 2a2 + 3a3 + 4a4 + 5a5 is equal to x;

[0039] - 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):

[0040] HO-(G)-H (III);

[0041] 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;

[0042] - the basic agent (Ab) is chosen from the elements of the group consisting of:

[0043] • carbonates of formula (IVa):

[0044] XnCO3 (IVa),

[0045] in which X represents a sodium or potassium atom and n is a number integer equal to 2, or X represents a calcium atom or a magnesium atom and n is an integer equal to 1, or

[0046]

[0047] hydrogen carbonates of formula (IVb): Y(HC03)m (IVb),

[0048] in which 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;

[0049] the basic agent (Ab) included in the aqueous solution used in step d) neutralization agent is chosen from sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3); step b) of pre-neutralization is carried out so as to obtain a reaction medium of which a dispersion at 5% by mass of said reaction medium in water has a pH value of between 3.5 and 5.5; step b) of pre-neutralization 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; step b) of pre-neutralization is carried out with one of the following compounds: sodium carbonate (Na2CO3), sodium hydrogen carbonate (NaHCO3), and calcium carbonate (CaCO3); step d) is carried out so as to obtain a reaction medium of which a dispersion at 5% by mass of said reaction medium in water has a pH value of between 5.5 and 7.5; 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; 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 sub-steps:

[0050] 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;

[0051] ii) Heating the alcohol of formula (I) to a temperature between 80°C and 90°C with mechanical stirring;

[0052] iii) Loading the reducing sugar of formula (II) into the reactor (Re);

[0053] iv) Introduction of the acid catalyst (CA) into the reactor (Re),

[0054] v) Partial vacuum heating of the reaction medium from sub-step iv) and present in the reactor (Ré) at a temperature between 100°C and 110°C for the duration of the reaction, and

[0055] vi) Cooling the reaction medium from sub-step v) to a temperature between 70°C and 80°C;

[0056] - 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-hydroxy stearyl; - 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); - the acid catalyst (AC) is chosen from the elements of 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 sub-steps ii) to iv) the reactor (Ré) is inerted under nitrogen; - the method comprises between sub-steps ii) and iii) a step of putting under vacuum, preferably at a pressure less than or equal to 50 millibars; - sub-step vi) is carried out at atmospheric pressure.

[0057] The use of carbonates of formula (IVa) or hydrogen carbonates of formula (IVb) does not contribute to increasing the color of the composition (C) (the presence of a reducing agent then not being necessary) while neutralizing at the desired pH of a dispersion at 5% by mass of the composition (C) (the value of which is between 5.5 and 7.5). The use of a basic agent (Ab) makes it possible to avoid a bleaching step involving the use of a peroxide agent, or others, since it makes it possible to achieve a color less than or equal to 1.5 vcs.

[0058] 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 they are defined in the reference work: “Biochemistry”, Daniel Voet / Judith G. Voet, p. 250, John Wyley & Sons, 1990.

[0059] The oligomeric structure (G)x present in formula (II) can be present in all forms of isomerism, whether optical isomerism, geometric isomerism or positional isomerism; it can also represent a mixture of isomers.

[0060] In formula (II) as defined above, the radical R is linked to G by the anomeric carbon of the saccharide residue, so as to form an acetal function.

[0061] According to a particular aspect of the present invention, in the definition of the compounds of formulas (II) and (III), G represents the residue of a reducing sugar chosen from glucose, dextrose, sucrose, fructose, idose, gulose, galactose, maltose, isomaltose, maltotriose, lactose, cellobiose, mannose, ribose, xylose, arabinose, lyxose, allose, altrose, rhamnose, dextran or tallose.

[0062] According to a particular aspect of the present invention, in the definition of the compounds of formula (II), G represents the residue of a reducing sugar chosen from the residues 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.

[0063] According to an even more particular aspect of the present invention, in the definition of the compounds of formula (II), G represents the residue of a reducing sugar chosen from the residues 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.

[0064] According to another particular aspect of the present invention, the reducing sugar of formula (III) is chosen 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.

[0065] According to a more particular aspect of the present invention, the reducing sugar of formula (III) is chosen from glucose, xylose, arabinose or rhamnose.

[0066] The method according to the invention consists in carrying out a pre-neutralization of the medium at the end of the glycosylation reaction to achieve a pH value of a 5% mass dispersion of said medium in water of between 3.5 and 5.5. This pre-neutralization can be carried out by an alkali metal or alkaline earth metal carbonate, an alkali metal or alkaline earth metal hydrogen carbonate or any other bases known to those skilled in the art. The residual reducing sugar of formula (II) is then removed by filtration and an aqueous solution of a basic agent (Ab) is added to achieve a pH value of the 5% mass dispersion in water of composition (C) of between 5.5 and 7.5.

[0067] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0068] - from 45% to 55% by mass of a mixture (Ml) of alcohols of formula (I) comprising for 100% of the mass of said mixture (Ml), 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 - from 45% to 54% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0069] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0070] - from 45% to 55% 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 - from 45% to 54% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0071] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0072] - from 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 - from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0073] According to a particular aspect, the method relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0074] - from 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'”l), 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 - from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0075] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0076] - from 75% to 90% by mass of an alcohol of formula (I) in which R represents the n-tetradecyl radical - from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0077] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0078] - from 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 - from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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 radical 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.

[0079] According to a particular aspect, the method relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0080] from 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 from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0081] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0082] from 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 from 10% to 24% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the glucosyl or a,[3-D-glucopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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.

[0083] According to a particular aspect, the process relates to the preparation of a composition (C) of color less than or equal to 1.5 VCS, comprising for 100% of its mass:

[0084] from 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 from 10% to 29% by mass of at least one composition (Cl) represented by the formula (II) in which G represents the xylosyl or a,[3-D-xylopyranosyl radical, obtained from the removal of the hemiacetal hydroxyl group of a,[3-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-octyl dodecyl radical less than 1% by mass of xylose.

[0085] According to a 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.

[0086] According to a 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.

[0087] According to a particular aspect, the acid catalyst (CA) is chosen from the elements of the group consisting of sulfuric acid, phosphoric acid, hypophosphorous acid, methanesulfonic acid, p-toluenesulfonic acid. EXAMPLES

[0088] Comparison of the effect of the neutralizing agent on the color of a composition of fatty alcohols and alkylpolyglucosides when the basic neutralizing agent used is a carbonate according to the invention or soda (comparative neutralizing agent).

[0089] Comparisons between a carbonate and sodium hydroxide as a neutralizing agent were made. For this, glycosylation reactions were carried out from crystallized glucose and different fatty alcohols in the form of cuts or pure: C-16 / 18 cetearyl cut, C-20 / 22 arachidyl / behenyl cut, 1-tetradecanol (C-14 alcohol) and 1-dodecanol (C-12 alcohol).

[0090] 1. Examples according to the invention

[0091] Example 1.1 (Cut of alcohols 16 / 18 and Na2CO3 as pre-neutralizing agent and neutralizing agent) according to the invention

[0092] STEP 1: Glycosylation reaction:

[0093] 967.4 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with a mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torr. A quantity of anhydrous glucose in powder form is added so that the molar ratio between fatty alcohols and glucose is 6 / 1. The medium is inerted under nitrogen. To start the etherification reaction, 0.9 g of a 50% aqueous solution of H3PO2 and then 1.1 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for a period of 5 hours 45 minutes.

[0094] STEP 2: Neutralization of the reaction medium:

[0095] The medium is then cooled to 80°C at atmospheric pressure and then pre-neutralized by introducing 2.21 g of a 25% aqueous Na2CO3 solution. The product is then introduced into a glass bottle and placed in an oven at 80°C for 5 hours in order to decant the residual glucose. The product (upper phase) is then filtered through filter paper (approximately 10 μm). A 5% mass dispersion in water shows a pH value of 4.7 and the product a color of 0.6 VCS. The product is then neutralized by introducing 4.61 g of a 25% aqueous Na2CO3 solution. The product is then introduced into a glass bottle and placed in an oven at 80°C for 24 hours in order to decant the residual glucose. The product (upper phase) is recovered and referenced (Composition 1).

[0096] Analyses:

[0097] - 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.

[0098] Example 1.2 (16 / 18 alcohol cut and NaOH as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention

[0099] STEP 1: Glycosylation reaction:

[0100] 1364.8 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with a mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torrs. 179.2 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 1.2 g of a 50% aqueous solution of H3PO2 and then 1.6 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5 hours 45 minutes.

[0101] STEP 2: Neutralization of the reaction medium:

[0102] 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 introduced into a glass bottle and placed in an oven at 80°C for 5 hours in order to decant the residual glucose. The product (upper phase) is then filtered through filter paper (~ 10 qm).

[0103] A 5% mass dispersion in water shows a pH value of 4.5 and the product a color of 1.0 VCS. The product (880 g) is then neutralized at 85°C in a stirred reactor, by introducing 3.57 g of a 10% aqueous Na2CO3 solution. The product is recovered and referenced (Composition 2).

[0104] Analyses:

[0105] - 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.

[0106] Example L3 (16 / 18 alcohol cut and NaOH as pre-neutralizing agent and NaHCO3 as neutralizing agent) according to the invention

[0107] STEP 1: Glycosylation reaction:

[0108] 271.1 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with a mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torr. 35.7 g of anhydrous glucose in powder form is added. The medium is inerted under nitrogen. To start the etherification reaction 0.2 g of a 50% aqueous solution of H3PO2 then 0.3 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5h45.

[0109] STEP 2: Neutralization of the reaction medium:

[0110] The medium is cooled to 85°C at atmospheric pressure and then pre-neutralized by introducing 0.4 g of a 25% aqueous NaOH solution with stirring. The product is then introduced into a glass bottle and placed in an oven at 80°C for 24 hours in order to decant the residual glucose. A 5% mass dispersion in water shows a pH value of 3.5 and the product a color of 0.5 VCS. The product (173.8 g) is then neutralized in a reactor at 85°C with stirring by introducing 1.9 g of an 8% aqueous NaHCO3 solution. The product is recovered and referenced (Composition 3). [YES] Analyses:

[0112] - 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.

[0113] Example 1.4 f Alcohol cut 20 / 22 and NaOH as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention

[0114] STEP 1: Glycosylation reaction:

[0115] 284.7 g of beneethyl / arachidyl alcohols (C-20 / 22) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torr. 29.2 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 0.3 g of a 50% aqueous solution of H3PO2 and then 0.4 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 4.5 hours.

[0116] STEP 2: Neutralization of the reaction medium:

[0117] The medium is cooled to 90°C at atmospheric pressure and then pre-neutralized by introducing 0.89 g of a 25% aqueous NaOH solution with stirring. The product is then introduced into a glass bottle and placed in an oven at 80°C for 24 hours in order to decant the residual glucose. A 5% mass dispersion in water shows a pH value of 5.1 and the product has a color of 0.3 VCS.

[0118] 175.4 g of product (upper phase) is then neutralized at 90°C in a reactor under stirring, introducing 0.61 g of a 10% aqueous solution of Na2CO3.

[0119] The product is recovered and referenced (Composition 4).

[0120] Analyses:

[0121] - 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.

[0122] Example 1.5 (Alcohol cut 20 / 22 and Na2CO3 as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention

[0123] STEP 1: Glycosylation reaction:

[0124] 391.9 g of beneethyl / arachidyl alcohol (C-20 / 22) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torr. 40.1 g of anhydrous glucose in powder form is added. The medium is inerted under nitrogen. To start the etherification reaction, 0.4 g of a 50% aqueous solution of H3PO2 and then 0.6 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 4.5 hours.

[0125] STEP 2: Neutralization of the reaction medium:

[0126] The medium 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 introduced into a glass bottle and placed in an oven at 105°C for 24 hours in order to decant the residual glucose. A 5% mass dispersion in water shows a pH value of 5.2 and the product 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.

[0127] The product is recovered and referenced (Composition 5).

[0128] Analyses:

[0129] - 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.

[0130] Example L6 (tetradecanol-1 and Na2CO3 as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention

[0131] STEP 1: Glycosylation reaction:

[0132] 428.7 g of C-14 myristyl alcohol (or tetradecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation setup. The alcohol is melted at 80°C and stirred and bubbling with nitrogen. The medium is evacuated to 35 Torr. 59.9 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 1.0 g of a 50% aqueous solution of H3PO2 and then 0.7 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5 hours.

[0133] STEP 2: Neutralization of the reaction medium:

[0134] The medium is cooled to 70°C at atmospheric pressure and then pre-neutralized in introducing 1.6 g of a 25% aqueous NaOH solution with stirring. The product is then introduced into a glass bottle and placed in an oven at 80°C for 24 hours to decant the residual glucose. A 5% mass dispersion in water shows a pH value of 5.2 and the product a color of 0.6 VCS. The product (337 g) is then neutralized at 70°C in a reactor with stirring, by introducing 0.7 g of a 10% aqueous Na2CO3 solution. The product is recovered and referenced (Composition 6).

[0135] Analyses:

[0136] - 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.

[0137] Example 1.7 (dodecanol-1 and Na2CO3 as pre-neutralizing agent and Na2CO3 as neutralizing agent) according to the invention

[0138] STEP 1: Glycosylation reaction:

[0139] 414.5 g of lauryl alcohol (C-12) (or dodecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbled with nitrogen. The medium is evacuated to 30 Torr. 57.9 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 0.4 g of a 50% aqueous solution of H3PO2 and then 0.7 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5 hours.

[0140] STEP 2: Neutralization of the reaction medium:

[0141] The medium is then cooled to 67°C at atmospheric pressure and then pre-neutralized by introducing 3.55 g of a 10% aqueous Na2CO3 solution. The product is filtered on a plate filter (~ 100 qm) in order to remove the residual glucose. A 5% mass dispersion in water shows a pH value of 3.7 and the product 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.

[0142] The product is recovered and referenced (Composition 7).

[0143] Analyses:

[0144] - 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. Comparative examples

[0145] Example 2.1: comparative example f Cut of alcohols 16 / 18 and NaOH as pre-neutralizing agent and NaOH as neutralizing agent)

[0146] STEP 1: Glycosylation reaction:

[0147] 778.1 g of cetearyl alcohol (C-16 / 18) are loaded into a reactor equipped with a mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to pressures below 50 Torr. 102.2 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 0.7 g of a 50% aqueous solution of H3PO2 and then 0.9 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5 hours 45 minutes.

[0148] STEP 2: Neutralization of the reaction medium:

[0149] The medium is then cooled to 80°C at atmospheric pressure and then pre-neutralized by introducing 1.86 g of a 25% aqueous NaOH solution. The product is then introduced into a glass bottle and placed in an oven at 80°C for 3 hours in order to decant the residual glucose. A 5% mass dispersion in water shows a pH value of 3.3 and the product has a color of 0.6 VCS.

[0150] The product is then neutralized at 80°C by introducing 0.28 g of a 25% aqueous NaOH solution. The product is recovered and referenced (Composition 1').

[0151] Analyses:

[0152] - 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.

[0153] Example 2.2: comparative example (C-12 alcohol and NaOH as pre-neutralizing agent and NaOH as neutralizing agent)

[0154] STEP 1: Glycosylation reaction:

[0155] 190.6 g of lauryl alcohol (C-12) (or dodecanol-1) are loaded into a reactor equipped with mechanical stirring and a vacuum distillation setup. The alcohol is melted at 85°C and stirred and bubbling with nitrogen. The medium is evacuated to 30 Torr. 26.6 g of anhydrous glucose in powder form are added. The medium is inerted under nitrogen. To start the etherification reaction, 0.2 g of a 50% aqueous solution of H3PO2 and then 0.3 g of a 98% aqueous solution of H2SO4 are added and the temperature is increased and maintained at 105°C. The reaction is continued for 5 hours.

[0156] STEP 2: Neutralization of the reaction medium:

[0157] The medium is then cooled to 75°C at atmospheric pressure and then pre-neutralized by introducing 0.70 g of a 25% aqueous NaOH solution with stirring. A 5% mass dispersion in water shows a pH value of 5.6 and the product has a color of 2.0 VCS. The product is filtered through a K200 filter (~ 3-6 qm) 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.

[0158] The product is recovered and referenced (Composition 2').

[0159] Analyses:

[0160] - 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. Observation and analysis of the results

[0161] The following Table 1 brings together the results of the process for preparing compositions (C) obtained by the reaction between glucose and C-16 / 18 alcohols (mixture of 1-hexadecanol and 1-octadecanioIol). The different parameters studied are: i) the nature of the pre-neutralization agent (Na2CO3 or NaOH) and / / ) the nature of the final neutralization agent (Na2CO3, NaHCO3 or NaOH).

[0162] 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 state of the art.

[0163] [Tables 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

[0164] These tests highlight that the presence of a pre-neutralization step using an aqueous NaOH solution and a neutralization step using an aqueous NaOH solution results in excessively high coloration of the composition obtained (up to 3.8 VCS for Composition 1'). In comparison, when the pre-neutralization step is carried out with a NaOH solution (Composition 2) or Na2CO3 (Composition 1) and the neutralization step is carried out with an aqueous Na2CO3 solution, the colors of the compositions obtained are very low (< 1 vcs).

[0165] For the preparation of Composition 3, the process according to the invention was implemented by carrying out a pre-neutralization step with an aqueous NaOH solution (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).

[0166] This test shows that it is possible to use hydrogen carbonate of sodium 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).

[0167] Table 2 brings together 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.

[0168] [Tables2] Reference Composition n4 Composition n 5 Composition n 6 Composition n 2' Composition n7 AlkylPoly-Glucoside 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

[0169] The process according to the invention makes it possible to obtain a composition (C), with low coloration (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.

[0170] 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, i.e. significantly higher than 1.5 VCS.

[0171] In conclusion, the process according to the invention makes it possible to obtain compositions comprising fatty alcohols and alkylpolyglycosides with little color (color 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

Claims

1. Process for preparing a composition (C) of color less 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, which may contain at least one hydroxyl function, and containing from twelve to twenty-two carbon atoms, or 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 of a composition (Cl) represented by formula (II) RO-(G)xH (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 1.05 and less than or equal to 2.5, or of a mixture of compositions (Cl) of formula (II); it being understood that the sum of the mass proportions of the compounds of formulae (I) and (II) in 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): HO-(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, b. A step b) of pre-neutralization of the reaction medium resulting from step a), c. A step c) of removing 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 step d) of neutralization of the reaction medium resulting from step c) with an aqueous solution comprising a basic agent (Ab), e. A step e) of recovering at least one composition (C) of color less than or equal to 1.5 vcs.

2. Method according to claim 1, characterized in that said composition (Cl) consists of a mixture of compounds represented by the formulae (III), (112), (113), (114) and (115): RO-(G)1-H (III), R-0-(G)2-H (112), R-0-(G)3-H (113), R-0-(G)4-H (114), R-0-(G)5-H (115), in the respective molar proportions al, a2, a3, a4 and a5, such that: • the sum: al+ a2 + a3 + a4 + a5 is equal to 1, and • the sum al + 2a2 + 3a3 + 4a4 + 5a5 is equal to x.

3. Method according to 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): HO-(G)-H (III); it being understood that the sum of the mass proportions of the compounds of formulas (I), (II) and (III) in the composition (C) is equal to 100% by mass.

4. Method according to one of claims 1 to 3, characterized in that the basic agent (Ab) is 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 atom or a magnesium atom and n is an integer equal to 1, or - hydrogen carbonates of formula (IVb): Y(HC03)m (IVb), in which Y represents a sodium or potassium atom and m is an integer equal to 1, or Y represents a calcium atom or a magnesium atony and m is an integer equal to 2.

5. Method according to claim 4, characterized in that the basic agent (Ab) included in the aqueous solution used in neutralization step d) is chosen from sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3).

6. Method according to one of claims 1 to 5, characterized in that step b) of pre-neutralization is carried out so as to obtain a reaction medium of which a dispersion at 5% by mass of said reaction medium in water has a pH value of between 3.5 and 5.

5.

7. Method according to one of claims 1 to 6, characterized in that step b) of pre-neutralization 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.

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

9. Method according to one of claims 1 to 8, characterized in that step d) is carried out so as to obtain a reaction medium of which a dispersion at 5% by mass of said reaction medium in water has a pH value of between 5.5 and 7.

5.

10. Process according to one of claims 1 to 9, 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.

11. Method according to one of claims 1 to 10, characterized in that step c) of removing the reducing sugar of formula (III) is carried out by filtration, centrifugation or decantation.

12. Method according to one of claims 1 to 11, 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).

13. Process according to one of claims 1 to 12, 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 (Re) equipped with mechanical stirring and a vacuum device; ii) Heating of the alcohol of formula (I) to a temperature between between 80°C and 90°C with mechanical stirring; iii) Loading the reducing sugar of formula (II) into the reactor (Re); iv) Introduction of the acid catalyst (CA) into the reactor (Re), v) Heating under partial vacuum the reaction medium from sub-step iv) and present in the reactor (Re) to a temperature between 100°C and 110°C for the duration of the reaction, and vi) Cooling the reaction medium from sub-step v) to a temperature between 70°C and 80°C.

14. Method according to claim 13, 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), pahnitoleyl (or 9-hexadecenyl), oleyl (or 9-octadecenyl), linoleyl (9,12-octadecadienyl), linolenyl (or 6,9,12-octadecatrienyl) no-nadecyl, arachidyl (or n-eicosyl), behenyl (or n-docosyl), erucyl (13-docosenyl), or 12-hydroxystearyl.

15. Method according to claim 13, 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).

16. Method according to one of claims 13 to 15, characterized in that the acid catalyst (CA) is chosen from the elements of 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.

17. Method according to one of claims 13 to 16, characterized in that during sub-steps ii) to iv) the reactor (Ré) is inerted under nitrogen.

18. Method according to one of claims 13 to 17, characterized in that it comprises between sub-steps ii) and iii) a vacuum step, preferably at a pressure less than or equal to 50 millibars.

19. Method according to one of claims 13 to 18, characterized in that sub-step vi) is carried out at atmospheric pressure.