PROCESS FOR THE PREPARATION OF LOW-COLOR ALKYL POLYGLYCOSIDES, INVOLVING PRE-NEUTRALIZATION OF THE REACTION MEDIUM

Abstract

Disclosed is a process for preparing alkyl polyglycosides having a color of less than or equal to 1.5 VCS, the method successively comprising: (a) a glycosylation step (a), consisting in 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 minimum temperature of 100° C. and a maximum temperature of 120° C.; (b) a step (b) of pre-neutralizing 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 neutralizing the reaction medium resulting from step (c) with an aqueous solution comprising a basic agent (Ab); and (e) a step (e) of recovering at least one composition (C) having a color less than or equal to 1.5 VCS.

Description

The present invention relates to a process for preparing low-color alkyl polyglycosides (color of less than 1.5 VCS) involving carbonate neutralizing agents.

Alkyl polyglycosides or APGs are probably the best examples of biobased 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 lipophilic hydrocarbon chain of varying length (cf. formula I: simplified structure of an APG).

The process for the industrial scale manufacture thereof is relatively simple and uses, as raw materials: i) crystalline glucose or xylose or rhamnose resulting respectively from the complete hydrolysis of wheat, corn or potato starch or from the hydrolysis of wood hemicelluloses; and ii) fatty alcohols from the oleochemical industry (hydrogenation of methyl esters resulting from the transesterification of plant triglycerides). Fischer glycosylation reactions then consist in linking these two raw materials together by creating a covalent chemical bond, like for example in reaction (II) between glucose and an alcohol.

To carry out this glycosylation reaction, an acid catalyst of mineral or organic origin is necessary and an excess of alcohols is systematically introduced, thus acting as reactant and solvent. At the end of the reaction, the APGs are dispersed or dissolved in the excess unreacted alcohol. APGs are distinguished by the nature and length of the hydrocarbon alkyl chain R and by their average degree of polymerization DP of greater than 1 but less than or equal to 2.5.

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

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

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 of 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-thin-film evaporator or a short-path thin-film evaporator, and the APG concentrate collected is finally dissolved in water. The commercial products thus obtained are therefore in the form of aqueous APG solutions with a weight concentration of between 40% and 80%.

In the case in which the hydrocarbon alkyl chain R has a number of carbon atoms of 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 such as described in the European patent published under number EP 0 077 167, in the European patent application published under number EP 0 338 151 A1, in the European patent EP 0 388 857 B1, for instance sodium borohydride (NaBH₄) or sodium hypophosphite (NaH₂PO₂). The mixture of APG and excess fatty alcohols is isolated after neutralization and is sold as is. The proportion of APGs and fatty alcohols depends on the molar stoichiometry adopted at the start for the raw materials and on their reactivity. However, proportions of from 5% to 30% by weight of APG and from 70% to 95% of fatty alcohols are generally observed. The compositions obtained may be in solid form, for instance in the form of flakes or beads, or in liquid form, depending on the nature of the hydrocarbon alkyl chain R.

However, the step of neutralizing APGs having a hydrocarbon alkyl chain R that contains a number of carbon atoms of greater than or equal to 12 with a base from the prior art (e.g. NaOH, KOH), in order to achieve a pH of a 5 wt % dispersion in water of the neutralized medium of between 5.5 and 7.5, gives rise to significant coloration of the product.

For the purposes of the present invention, “measurement of the pH of a 5 wt % dispersion in water” denotes the analytical method for measuring the pH of a dispersion of an APG-based composition according to the provisions of NF EN 1262; said measurement is carried out by potentiometric measurement using a combined pH electrode (aqueous media) and a pH meter.

This coloration may impair the organoleptic qualities of the finished products into which the APG compositions are introduced. For this reason, solutions are provided to minimize the coloration of compositions containing APGs having a hydrocarbon alkyl chain R that contains a number of carbon atoms of greater than or equal to 12. Two solutions known from the prior art are conventionally used to obtain such low-color (<1.5 VCS) compositions based on APGs having a hydrocarbon alkyl chain R that contains a number of carbon atoms of greater than or equal to 12.

For the purposes of the present invention, a “low-color composition” denotes a composition for which the Gardner color scale, as defined by DIN-ISO 4630, is less than or equal to 1.5 VCS. The Gardner color scale is measured using a LICO 200/Dr LANGE (or equivalent) colorimeter that performs light transmission measurements 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 with a 2° field of view. During the measurement, a reference radiation beam compensates for variations in the recorded values due to lamp and temperature differences.

The first solution consists in combining a reducing agent with the base used. Among these reducing agents, mention may be made of sodium borohydride (NaBH₄) or of sodium hypophosphite (NaH₂PO₂). This solution is not entirely satisfactory. Specifically, although very effective in minimizing the coloration of the treated composition, NaBH₄ is a reducing agent which is hazardous to handle and to use (corrosive product, release of hydrogen). NaH₂PO₂ is itself not very effective, even if it is introduced at high concentration.

The second solution commonly used and described in the prior art for minimizing the color of compositions based on APGs having a hydrocarbon alkyl chain R that contains a number of carbon atoms of greater than or equal to 12 is carrying out a decolorization with hydrogen peroxide (H₂O₂) during the finishing step. Although effective, this step is however tedious because it requires the pH value of a 5 wt % dispersion in water to be adjusted to between 7.0 and 7.5 while maintaining the oxidizing power of the medium by adding H₂O₂. This step, which is difficult to carry out, can last several hours and therefore significantly increase the production time, reducing productivity.

The technical problem to be solved is therefore that of finding an alternative to the neutralization of APG compositions having a hydrocarbon alkyl chain R that contains a number of carbon atoms of greater than or equal to 12. This alternative must be effective and easy to implement, while guaranteeing a color of less than or equal to 1.5 VCS without carrying out a decolorization step.

One solution of the present invention is a process for preparing a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • i) an amount of greater than or equal to 40% by weight and less than or equal to 95% by weight, preferably greater than or equal to 50% by weight and less than or equal to 95% by weight, even more preferentially greater than or equal to 70% by weight and less than or equal to 90% by weight of an alcohol of formula (I):

R—OH  (I),

• • • wherein R represents a linear or branched, saturated or unsaturated hydrocarbon radical, which may contain at least one hydroxyl function, and containing from 12 to 22 carbon atoms, or a mixture of alcohols of formula (I);
  • ii) an amount of greater than or equal to 5% by weight and less than or equal to 60% by weight, preferably greater than or equal to 5% by weight and less than or equal to 50% by weight, even more preferentially greater than or equal to 10% by weight and less than or equal to 30% by weight of a composition (C1) represented by formula (II):

R—O-(G)x-H  (II),

wherein 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 a mixture of compositions (C1) of formula (II);

• • it being understood that the sum of the weight proportions of the compounds of formulae (I) and (II) in composition (C) is equal to 100% by weight,
  • said process successively comprising:
  • a) 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): H—O-(G)-H (III), in the presence of at least one acid catalyst (CA), at a temperature of greater than or equal to 100° C. and less than or equal to 120° C., preferentially greater than or equal to 100° C. and less than or equal to 115° C., even more preferentially greater than or equal to 100° C. and less than or equal to 110° C., the acid catalyst (CA) being selected from members 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,
  • b) a step b) of pre-neutralizing the reaction medium from step a), the pre-neutralization being carried out so as to obtain a reaction medium for which the 5 wt % dispersion of said reaction medium in water has a pH of 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) selected from the members 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
    • hydrogen carbonates 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 for which the 5 wt % dispersion of said reaction medium in water has a pH of between 5.5 and 7.5, and
  • e) a step e) of recovering at least one composition (C) having a color of less than or equal to 1.5 VCS.

The color scale characterizing the composition (C) prepared according to the process which is the subject of the present invention is the Gardner color scale, as defined by DIN-ISO 463. The Gardner color scale is measured using a LICO 200/Dr LANGE (or equivalent) colorimeter that performs light transmission measurements 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 with a 2° field of view. During the measurement, a reference radiation beam compensates for variations in the recorded values due to lamp and temperature differences.

The unit for expressing the Gardner color scale, characterizing the composition (C) prepared according to the process which is the subject of the present invention, is VCS.

Depending on the case, the process according to the invention may have one or more of the following characteristics:

• • 1 said composition (C1) consists of a mixture of compounds represented by formulae (II1), (II2), (II3), (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;
  • the composition (C) comprises an amount of less than or equal to 2% by weight, more particularly less than or equal to 1% by weight, of the reducing sugar of formula (III):

H—O-(G)-H  (III);

• • it being understood that the sum of the weight proportions of the compounds of formulae (I), (II) and (III) in composition (C) is equal to 100% by weight;
  • the basic agent (Ab) contained in the aqueous solution used in the neutralization step d) is selected from sodium carbonate (Na₂CO₃) or sodium hydrogen carbonate (NaHCO₃);
  • 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;
  • the pre-neutralization step b) is carried out with one of the following compounds: sodium carbonate (Na₂CO₃), sodium hydrogen carbonate (NaHCO₃), and calcium carbonate (CaCO₃);
  • the reducing sugar of formula (III) chosen for the glycosylation of step a) is selected from the members of the group consisting of glucose, xylose, arabinose and rhamnose;
  • step c) of removing the reducing sugar of formula (III) is carried out by filtration, centrifugation or settling;
  • in step d), the aqueous solution of basic agent (Ab) comprises between 10% and 25% by weight of said basic agent (Ab);
  • step a) comprises the following successive substeps:
    • i) introducing an alcohol of formula (I) or a mixture of alcohols of formula (I) into a reactor (Re) equipped with a mechanical stirrer and a vacuum device;
    • ii) heating the alcohol of formula (I) to a temperature of between 80° C. and 90° C. under mechanical stirring;
    • iii) charging the reducing sugar of formula (III) to the reactor (Re);
    • iv) introducing the acid catalyst (CA) into the reactor (Re);
    • v) heating, under partial vacuum, the reaction medium from substep iv) present in the reactor (Re) to a temperature of between 100° C. and 110° C. for the duration of the reaction, and
    • vi) cooling the reaction medium from substep v) to a temperature of between 70° C. and 80° C.;
  • the radical R is selected 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.
  • the radical R is selected from the following radicals: 2-hexyloctyl, 2-hexyldecyl, 2-hexyldodecyl, 2-octyldecyl, 2-octyldodecyl, 2-decyltetradecyl, isostearyl (or 16-methylheptadecyl) or isomyristyl (or 13-methyltridecyl);
  • the acid catalyst (CA) is selected from the members 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 substeps ii) to iv), the reactor (Re) is inerted under nitrogen;
  • the process comprises, between substeps ii) and iii), a vacuum step, preferably at a pressure of less than or equal to 50 millibar;
  • substep vi) is carried out at atmospheric pressure.

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 a 5 wt % dispersion of the composition (C) to the desired pH (the value of which is between 5.5 and 7.5). The use of a basic agent (Ab) makes it possible to avoid a decolorization step involving the use of a peroxide agent, or the like, since it makes it possible to achieve a color less than or equal to 1.5 VCS.

The term “reducing sugar” in the definition of formula (II) and in the definition of formula (III) denotes saccharide derivatives that do not have in their structures any glycosidic bonds established between an anomeric carbon and the oxygen of an acetal group, as they are defined in the reference publication: “Biochemistry”, Daniel Voet/Judith G. Voet, page 250, John Wiley & Sons, 1990.

The oligomeric structure (G)x present in formula (II) may be in any isomeric form, whether this relates to optical isomerism, geometrical isomerism or regioisomerism; it may also represent a mixture of isomers.

In formula (II) as defined above, the radical R is bonded to G via the anomeric carbon of the saccharide residue, so as to form an acetal function.

According to a particular aspect of the present invention, in the definition of the compounds of formulae (II) and of formula (III), G represents the residue 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.

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 selected 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.

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 selected 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.

According to another particular aspect of the present invention, the reducing sugar of formula (III) is selected from the members 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.

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

The process according to the invention consists in pre-neutralizing the medium at the end of the glycosylation reaction in order to achieve a pH of a 5 wt % dispersion in water of said medium of between 3.5 and 5.5. This pre-neutralization can be carried out using 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 subsequently removed by filtration and an aqueous solution of a basic agent (Ab) is added to achieve a pH of the 5 wt % dispersion in water of the composition (C) of between 5.5 and 7.5.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 45% to 55% by weight of a mixture (M1) of alcohols of formula (I) comprising, for 100% of the weight of said mixture (M1), 50% by weight of an alcohol of formula (I) wherein R represents the n-hexadecyl radical and 50% by weight of an alcohol of formula (I) wherein R represents the n-octadecyl radical;
  • from 45% to 54% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 45% to 55% by weight of a mixture (M′1) of alcohols of formula (I) comprising, for 100% of the weight of said mixture (M′1), 70% by weight of an alcohol of formula (I) wherein R represents the n-hexadecyl radical and 30% by weight of an alcohol of formula (I) wherein R represents the n-octadecyl radical,
  • from 45% to 54% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of a mixture (M″1) of alcohols of formula (I) comprising, for 100% of the weight of said mixture (M″1), 50% by weight of an alcohol of formula (I) wherein R represents the n-hexadecyl radical and 50% by weight of an alcohol of formula (I) wherein R represents the n-octadecyl radical,
  • from 10% to 24% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of a mixture (M″′1) of alcohols of formula (I) comprising, for 100% of the weight of said mixture (M″′1), 70% by weight of an alcohol of formula (I) wherein R represents the n-hexadecyl radical and 30% by weight of an alcohol of formula (I) wherein R represents the n-octadecyl radical,
  • from 10% to 24% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of an alcohol of formula (I) wherein R represents the n-tetradecyl radical;
  • from 10% to 24% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of a mixture of alcohols of formula (I) wherein R represents the n-dodecyl radical, the n-tetradecyl radical, the n-hexadecyl radical and the n-octadecyl radical;
  • from 10% to 24% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of a mixture of alcohols of formula (I) wherein R represents the n-eicosyl radical and the n-docosyl radical;
  • from 10% to 24% by weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 75% to 90% by weight of a mixture of alcohols of formula (I) wherein 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 weight of at least one composition (C1) represented by formula (II) wherein 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 of 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 weight of glucose.

According to a particular aspect, one subject of the process is the preparation of a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight:

• • from 70% to 90% by weight of a mixture of alcohols of formula (I) wherein 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 weight of a composition (C1) represented by formula (II) wherein 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 of 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 weight of xylose.

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

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

According to a particular aspect, the acid catalyst (CA) is selected from the members of the group consisting of sulfuric acid, phosphoric acid, hypophosphorous acid, methanesulfonic acid and p-toluenesulfonic acid.

EXAMPLES

Comparison of the Effect of the Neutralizing Agent on the Color of a Composition of Fatty Alcohols and Alkyl Polyglucosides when the Neutralizing Basic Agent Used is a Carbonate According to the Invention or Sodium Hydroxide (Comparative Neutralizing Agent).

Comparisons were made between a carbonate and sodium hydroxide as neutralizing agent. To this end, glycosylation reactions were carried out proceeding from crystalline glucose and various fatty alcohols, either in the form of cuts or in pure form: C16/18 cetearyl cut, C20/22 arachidyl/behenyl cut, 1-tetradecanol (C14 alcohol) and 1-dodecanol (C12 alcohol).

1. Examples According to the Invention

Example 1.1 (Cut of 16/18 Alcohols and Na₂CO₃ as Pre-Neutralizing Agent and Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

967.4 g of cetearyl alcohol (C16/18) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 50 Torr. An amount of anhydrous glucose in powder form is added such that the molar ratio of fatty alcohols to 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 duration of 5 hours 45 minutes.

Step 2: Neutralization of the Reaction Medium:

The medium is subsequently cooled to 80° C. at atmospheric pressure, then pre-neutralized by introducing 2.21 g of a 25% aqueous solution of Na₂CO₃. The product is subsequently introduced into a glass vial and placed in an oven at 80° C. for 5 hours in order to settle out the residual glucose. The product (upper phase) is subsequently filtered on filter paper (approximately 10 μm). A 5 wt % dispersion in water has a pH of 4.7, and the product has a color of 0.6 VCS. The product is subsequently neutralized by introducing 4.61 g of a 25% aqueous solution of Na₂CO₃. The product is subsequently introduced into a glass vial and placed in an oven at 80° C. for 24 hours in order to settle out the residual glucose. The product (upper phase) is recovered and referenced (Composition 1).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 1 is 6.8, and
  • the color measurement of Composition 1 is 0.5 VCS.

Example 1.2 (Cut of 16/18 Alcohols and NaOH as Pre-Neutralizing Agent and Na₂CO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

1364.8 g of cetearyl alcohol (C16/18) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 50 Torr. 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.

Step 2: Neutralization of the Reaction Medium:

The medium is cooled to 80° C. at atmospheric pressure, then pre-neutralized by introducing 3.4 g of a 25% aqueous solution of NaOH with stirring. The product is subsequently introduced into a glass vial and placed in an oven at 80° C. for 5 hours in order to settle out the residual glucose. The product (upper phase) is subsequently filtered on filter paper (^˜10 μm).

A 5 wt % dispersion in water has a pH of 4.5, and the product has a color of 1.0 VCS. The product (880 g) is subsequently neutralized at 85° C. in a reactor with stirring, by introducing 3.57 g of a 10% aqueous solution of Na₂CO₃. The product is recovered and referenced (Composition 2).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 2 is 7.2, and
  • the color measurement of Composition 2 is 0.9 VCS.

Example 1.3 (Cut of 16/18 Alcohols and NaOH as Pre-Neutralizing Agent and NaHCO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

271.1 g of cetearyl alcohol (C16/18) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 50 Torr. 35.7 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 45 minutes.

Step 2: Neutralization of the Reaction Medium:

The medium is cooled to 85° C. at atmospheric pressure, then pre-neutralized by introducing 0.4 g of a 25% aqueous solution of NaOH with stirring. The product is subsequently introduced into a glass vial and placed in an oven at 80° C. for 24 hours in order to settle out the residual glucose. A 5 wt % dispersion in water has a pH of 3.5, and the product has a color of 0.5 VCS. The product (173.8 g) is subsequently neutralized in a reactor at 85° C. with stirring, by introducing 1.9 g of an 8% aqueous solution of NaHCO₃. The product is recovered and referenced (Composition 3).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 3 is 6.3, and
  • the color measurement of Composition 3 is 0.4 VCS.

Example 1.4 (Cut of 20/22 Alcohols and NaOH as Pre-Neutralizing Agent and Na₂CO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

284.7 g of behenyl/arachidyl alcohols (C20/22) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 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 hours 30 minutes.

Step 2: Neutralization of the Reaction Medium:

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

175.4 g of product (upper phase) is subsequently neutralized at 90° C. in a reactor with stirring, by introducing 0.61 g of a 10% aqueous solution of Na₂CO₃.

The product is recovered and referenced (Composition 4).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 4 is 6.8, and
  • the color measurement of Composition 4 is 0.5 VCS.

Example 1.5 (Cut of 20/22 Alcohols and Na₂CO₃ as Pre-Neutralizing Agent and Na₂CO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

391.9 g of behenyl/arachidyl alcohol (C20/22) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 50 Torr. 40.1 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 0.6 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 hours 30 minutes.

Step 2: Neutralization of the Reaction Medium:

The medium is cooled to 90° C. at atmospheric pressure, then pre-neutralized by introducing 2.1 g of a 25% aqueous solution of Na₂CO₃ with stirring. The product is subsequently introduced into a glass vial and placed in an oven at 105° C. for 24 hours in order to settle out the residual glucose. A 5 wt % dispersion in water has a pH of 5.2, and the product has a color of 0.7 VCS. The product (266 g) is subsequently neutralized at 90° C. in a reactor with stirring, by introducing 0.1 g of a 25% aqueous solution of Na₂CO₃.

The product is recovered and referenced (Composition 5).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 5 is 6.5, and
  • the color measurement of Composition 5 is 0.7 VCS.

Example 1.6 (1-Tetradecanol and Na₂CO₃ as Pre-Neutralizing Agent and Na₂CO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

428.7 g of myristyl C14 alcohol (or 1-tetradecanol) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 80° C., stirred and sparged with nitrogen. The medium is placed under vacuum at 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.

Step 2: Neutralization of the Reaction Medium:

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

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 6 is 7.3, and
  • the color measurement of Composition 6 is 0.7 VCS.

Example 1.7 (1-Dodecanol and Na₂CO₃ as Pre-Neutralizing Agent and Na₂CO₃ as Neutralizing Agent) According to the Invention

Step 1: Glycosylation Reaction:

414.5 g of lauryl alcohol (C12) (or 1-dodecanol) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at 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.

Step 2: Neutralization of the Reaction Medium:

The medium is subsequently cooled to 67° C. at atmospheric pressure, then pre-neutralized by introducing 3.55 g of a 10% aqueous solution of Na₂CO₃. The product is filtered on a filter plate (^˜100 μm) in order to remove the residual glucose. A 5 wt % dispersion in water has a pH of 3.7, and the product has a color of 1.1 VCS. The product (197 g) is subsequently neutralized in a reactor at 67° C., by introducing 2.97 g of a 10% aqueous solution of Na₂CO₃ with stirring. The product is recovered and referenced (Composition 7).

Analyses:

• • the pH of a 5 wt % 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 (Cut of 16/18 Alcohols and NaOH as Pre-Neutralizing Agent and NaOH as Neutralizing Agent)

Step 1: Glycosylation Reaction:

778.1 g of cetearyl alcohol (C16/18) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at pressures of less than 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.

Step 2: Neutralization of the Reaction Medium:

The medium is subsequently cooled to 80° C. at atmospheric pressure, then pre-neutralized by introducing 1.86 g of a 25% aqueous solution of NaOH. The product is subsequently introduced into a glass vial and placed in an oven at 80° C. for 3 hours in order to settle out the residual glucose. A 5 wt % dispersion in water has a pH of 3.3, and the product has a color of 0.6 VCS.

The product is subsequently neutralized at 80° C. by introducing 0.28 g of a 25% aqueous solution of NaOH. The product is recovered and referenced (Composition 1′).

Analyses:

• • the pH of a 5 wt % 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 (C12 Alcohol and NaOH as Pre-Neutralizing Agent and NaOH as Neutralizing Agent)

Step 1: Glycosylation Reaction:

190.6 g of lauryl alcohol (C12) (or 1-dodecanol) are charged to a reactor equipped with a mechanical stirrer and a vacuum distillation setup. The alcohol is melted at 85° C., stirred and sparged with nitrogen. The medium is placed under vacuum at 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.

Step 2: Neutralization of the Reaction Medium:

The medium is subsequently cooled to 75° C. at atmospheric pressure, then pre-neutralized by introducing 0.70 g of a 25% aqueous solution of NaOH with stirring. A 5 wt % dispersion in water has a pH of 5.6, and the product has a color of 2.0 VCS. The product is filtered on a K200 filter (^˜3-6 μm) in order to remove the residual glucose. The product (78 g) is subsequently neutralized in a reactor at 80° C., by introducing 0.08 g of a 25% aqueous solution of NaOH with stirring.

The product is recovered and referenced (Composition 2′).

Analyses:

• • the pH of a 5 wt % dispersion in water of Composition 2′ is 6.5, and
  • the color measurement of Composition 2′ is 4.5 VCS.

3. Observations and Analysis of the Results

Table 1 below collates the results of the process for preparing compositions (C) obtained by reaction between glucose and C16/18 alcohols (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).

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
		Com-	Com-	Com-	Com-
		position	position	position	position
	Reference	1′	1	2	3
	Pre-neutralizing	NaOH	Na2CO3	NaOH	NaOH
	agent
	Neutralizing	NaOH	Na2CO3	Na2CO3	NaHCO3
	agent
	pH of 5%	6.2	6.8	7.2	6.3
	dispersion in
	water
	Color (VCS)	3.8	0.5	0.9	0.4

These tests demonstrate that the presence of a step of pre-neutralization with an aqueous solution of NaOH and of a step of neutralization with an aqueous solution of NaOH leads to too great a 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 solution of NaOH (Composition 2) or Na₂CO₃ (Composition 1) and the neutralization step is carried out with an aqueous solution of Na₂CO₃, the colors of the products obtained are very low (<1 VCS).

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

This test demonstrates that it is possible to use sodium hydrogen carbonate during the neutralization step of the process according to the invention in order to guarantee low coloration of the desired Compositions (because the final color obtained is 0.4 VCS for Composition 3).

Table 2 collates the results of the process for preparing compositions (C) obtained by reaction between glucose and C20/22 alcohols (mixture of 1-eicosanol and 1-docosanol), between glucose and C14 alcohol (or 1-tetradecanol), between glucose and C12 alcohol (or 1-dodecanol), studying the same parameters as those involved in the above study.

TABLE 2
	Com-	Com-	Com-	Com-	Com-
	position	position	position	position	position
Reference	4	5	6	2′	7
Alkyl poly-	C20/22	C14	C12
glucoside chain
Pre-neutralizer	NaOH	Na2CO3	NaOH	NaOH	Na2CO3
Neutralizer	Na2CO3	Na2CO3	Na2CO3	NaOH	Na2CO3
pH of 5%	6.8	6.5	7.3	6.5	6.1
dispersion in
water
Color (VCS)	0.5	0.7	0.7	4.5	1.5

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

In contrast, 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.

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

Claims

1. A process for preparing a composition (C) having a color of less than or equal to 1.5 VCS, comprising, for 100% of its weight: i) an amount of greater than or equal to 40% by weight and less than or equal to 95% by weight of an alcohol of formula (I): R—OH  (I),wherein R represents a linear or branched, saturated or unsaturated hydrocarbon radical, which may contain at least one hydroxyl function, and containing from 12 to 22 carbon atoms, or a mixture of alcohols of formula (I);ii) an amount of greater than or equal to 5% by weight and less than or equal to 60% by weight of a composition (C1) represented by formula (II): R—O-(G)x-H  (II),wherein 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 a mixture of compositions (C1) of formula (II);it being understood that the sum of the weight proportions of the compounds of formulae (I) and (II) in composition (C) is equal to 100% by weight,said process successively comprising:a) 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): H—O-(G)-H (III), in the presence of at least one acid catalyst (CA), at a temperature of greater than or equal to 100° C. and less than or equal to 120° C., the at least one acid catalyst (CA) being selected from members 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,b) a step b) of pre-neutralizing the reaction medium from step a), the pre-neutralization being carried out so as to obtain a reaction medium for which the 5 wt % dispersion of said reaction medium in water has a pH of 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) selected from the members 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 hydrogen carbonates 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 for which the 5 wt % dispersion of said reaction medium in water has a pH of between 5.5 and 7.5, ande) a step e) of recovering at least one composition (C) having a color of less than or equal to 1.5 VCS.

2. The process as claimed in claim 1, characterized in that said composition (C1) consists of a mixture of compounds represented by formulae (III), (II2), (II3), (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, andthe sum a1+2a2+3a3+4a4+5a5 is equal to x.

3. The process as claimed in claim 1, characterized in that the composition (C) comprises an amount of less than or equal to 2% by weight, more particularly less than or equal to 1% by weight, of the reducing sugar of formula (III): H—O-(G)-H  (III);it being understood that the sum of the weight proportions of the compounds of formulae (I), (II) and (III) in composition (C) is equal to 100% by weight.

4. The process as claimed in claim 1, characterized in that the basic agent (Ab) contained in the aqueous solution used in the neutralization step d) is selected from sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3).

5. The process as claimed in claim 1, 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 as claimed in claim 1, characterized in that the pre-neutralization step b) is carried out with one of the following compounds: sodium carbonate (Na2CO3), sodium hydrogen carbonate (NaHCO3), and calcium carbonate (CaCO3).

7. The process as claimed in claim 1, characterized in that the reducing sugar of formula (III) selected for the glycosylation of step a) is selected from the members of the group consisting of glucose, xylose, arabinose and rhamnose.

8. The process as claimed in claim 1, characterized in that step c) of removing the reducing sugar of formula (III) is carried out by filtration, centrifugation or settling.

9. The process as claimed in claim 1, characterized in that, in step d), the aqueous solution of basic agent (Ab) comprises between 10% and 25% by weight of said basic agent (Ab).

10. The process as claimed in claim 1, characterized in that step a) comprises the following successive substeps: i) introducing an alcohol of formula (I) or a mixture of alcohols of formula (I) into a reactor (Re) equipped with a mechanical stirrer and a vacuum device;ii) heating the alcohol of formula (I) to a temperature of between 80° C. and 90° C. under mechanical stirring;iii) charging the reducing sugar of formula (III) to the reactor (Re);iv) introducing the acid catalyst (CA) into the reactor (Re);v) heating, under partial vacuum, the reaction medium from substep iv) present in the reactor (Re) to a temperature of between 100° C. and 110° C. for the duration of the reaction, andvi) cooling the reaction medium from substep v) to a temperature of between 70° C. and 80° C.

11. The process as claimed in claim 10, characterized in that the radical R is selected 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 as claimed in claim 10, characterized in that the radical R is selected from the following radicals: 2-hexyloctyl, 2-hexyldecyl, 2-hexyldodecyl, 2-octyldecyl, 2-octyldodecyl, 2-decyltetradecyl, isostearyl (or 16-methylheptadecyl) or isomyristyl (or 13-methyltridecyl).

13. The process as claimed in claim 10, characterized in that, during substeps ii) to iv), the reactor (Re) is inerted under nitrogen.

14. The process as claimed in claim 10, characterized in that it comprises, between substeps ii) and iii), a vacuum step, preferably at a pressure of less than or equal to 50 millibar.

15. The process as claimed in claim 10, characterized in that substep vi) is carried out at atmospheric pressure.