METHOD FOR THE PREPARATION OF N-ACYLAMINOSIC ACID BY DIRECT AMIDIFICATION OF A FAT ACID AT HIGH TEMPERATURE

Description

[0001] The present invention relates to a method for preparing an N-acylated compound of amino acids.

[0002] N-acylated derivatives of amino acids, also called LipoAminoAcids (LAA), are anionic surfactants, which consist of a polar head derived from a residue of at least one amino acid, or from a residue of (oligo)-peptides or from residues of partial or total hydrolysates of proteins, and by a hydrocarbon chain of a lipophilic nature, derived from acid chlorides or methyl esters or fatty acids or even triglycerides, themselves derived from the oleochemical process.

[0003] These N-acylated derivatives of amino acids, (oligo)-peptides or partial or total hydrolysates of proteins, are commonly used first of all as ingredients providing foaming and cleansing properties for the preparation of cosmetic compositions, such as shower gels or shampoos, or as ingredients providing biological properties for the preparation of cosmetic compositions intended to prevent or correct unsightly effects of the skin; said biological properties are for example anti-aging, moisturizing, slimming, firming, brightening, depigmenting, pro-pigmenting properties.

[0004] The preparation process commonly used for the preparation of such N-acylated derivatives of amino acids, (oligo)-peptides or partial or total hydrolysates of proteins is known to those skilled in the art as the Schotten-Baumann reaction.

[0005] Such a process is disclosed for example in US patents US 2,463,779 and US 6,703,517, in the publication J. Am. Oil Chem. Soc. - 78 (1956) 172, and in the international applications published under numbers WO 92 / 21318 and WO 94 / 26694.

[0006] This acylation process includes a preliminary step of salification of the amino acid, followed by a step of acylation of the amino acid salt with an acid chloride, and then acidification of the resulting N-acylated salt.

[0007] The first step (see diagram (1)) consists of neutralizing the amino acid, previously dissolved in water or in a mixture of water and an organic co-solvent, with a mineral base, most often sodium hydroxide or aqueous potassium hydroxide. The carboxyl group is then in an ionized form, thus improving the solubility of the amino acid in water. The pH of this aqueous solution is between 9.0 and 12.0, which ensures that the amine group of the amino acid is not protonated.

[0008] The second step (see Diagram 2) is the actual acylation step. At this stage, the acid chloride is gradually added to the neutralized amino acid solution at room temperature. The nucleophilic amine group attacks the electrophilic carbon of the carbonyl group. This results in the formation of an amide bond between the two starting substrates and the formation of hydrochloric acid. This acid is directly neutralized in situ by progressive addition of a mineral base (regulation of pH around 10.0).

[0009] At this stage, the secondary reaction of hydrolysis of the acid chloride to soap (see Scheme 3) is also possible. However, it must be minimized to achieve satisfactory conversion of the amino acid to its N-acylated derivative and to isolate them effectively, as an excessively high soap content can induce phase separation of the reaction medium and / or odor or toxicity problems (e.g., C8 and C11' chains).

[0010] The two main reaction parameters that allow control of soap formation are: i) - The speed of stirring during the reaction phase, the optimization of which allows an improvement of the contact surface of the acid chloride with the medium, and ii) - the possible addition, during the step of solubilization of the amino acid, of an acylation co-solvent, such as acetone, methyl ethyl ketone, isopropanol, or glycols.

[0011] This addition of a co-solvent improves the affinity of the acid chloride with the reaction medium. In such a case, the acylation co-solvent must be carefully chosen to avoid or minimize the formation of new byproducts from the reaction between this same co-solvent and the acid chloride, such as byproducts from esterification side reactions.

[0012] The final step consists of a finishing step, shaping the N-acylated derivative formed, and three alternatives are possible: i) The first method involves adjusting the pH of the reaction mixture to around 7. The N-acylated derivative is isolated as is in solution, without any further purification, and includes the acylation salts, unreacted amino acids, and any co-solvent. It is thus in a salt form, specifically a carboxylate form, in aqueous solution with a purity generally less than 50%. ii) The second method involves precipitating the N-acylated derivative by acidifying the reaction mixture to a pH close to 2, followed by several filtration and washing operations of the organic phase, concluding with final drying of the resulting mixture. iii) The third method, generally used for low-melting-point N-acylated derivatives, is based on hot acidification (pH ~ 2) to separate the acidic N-acylated derivative from the aqueous phase (called the "mother liquor").After decanting this aqueous phase, several washes of the organic phase containing the N-acylated derivative can be carried out by liquid / liquid decantation. The N-acylated derivative is finally shaped by freezing and grinding.

[0013] These last two procedures thus allow for the elimination of all salts generated during the acylation reaction, any acylation co-solvent, and all unreacted amino acids. In this case, the N-acylated amino acid derivative is in a non-salted form, with a carboxylic acid functional group, and in a solid, more specifically powdery, form with a purity exceeding 80%.

[0014] The previously described Schotten-Baumann process has the advantage of carrying out N-acylation reactions of amino acids with rapid kinetics, due to the very high reactivity of acid chlorides towards nucleophilic compounds and functions (for example the amine function), without significant energy input such as thermal energy, in a solvent medium mainly composed of water, with high yields.

[0015] This process has the disadvantages of conducting reactions in dilute media, which reduces their productivity; using acid chlorides as raw materials, obtained previously by reactions involving thionyl chloride or phosphoric trichloride as reactants, known for their danger; using organic co-solvents that are difficult to recycle; and inducing large quantities of inorganic salts, thus requiring the treatment of wash water.

[0016] To overcome these drawbacks, there are alternatives to the Schotten-Baumann process which include direct amidation of an amino acid by a fatty acid.

[0017] Document FR3066195A describes a process for preparing N-acylated amino acid derivatives based on the reaction of a cyclic amino acid with a fatty carboxylic acid at a temperature between 135°C and 155°C for a duration of 4 to 10 hours. The amino acid can be added by successive additions or by progressive pouring of a solution of the amino acid diluted in water. This process concerns cyclic amino acids such as proline and hydroxyproline. Their cyclic structure enhances the nucleophilicity of the endocyclic amine group, which compensates for the loss of reactivity associated with the substitution of acid chlorides by fatty acids.

[0018] Document FR3066194A describes a process for preparing N-acylated amino acid derivatives by reacting a fatty acid and an amino acid in the presence of a "starter" at a temperature of approximately 150°C for a period of 8 to 20 hours. A "starter" is defined as the use of a portion of the product to be synthesized as a reaction solvent. In this process, the desired N-acylated amino acid derivative is used as the reaction solvent. This N-acylated amino acid derivative used as a "starter" can be obtained either via a process specified in the application or via a Schotten-Baumann process. The N-acylated amino acid derivative used as a "starter" is liquid at the intended reaction temperatures and thus allows the amino acid to be solubilized.The main drawback of this alternative is the required amount of N-acylated amino acid derivative foot, which can constitute up to 30% by mass of the reaction medium.

[0019] For both of these processes, the temperatures and reaction times lead to very colored end products (brown to black), which implies mandatory post-reaction treatments to obtain products intended for use in cosmetic or pharmaceutical applications.

[0020] US patent 2016 / 0052869 describes a method for preparing N-acylated amino acid derivatives from fatty acids and amino acids at a temperature between 115°C and 160°C, in the presence of a dehydrating salt (such as magnesium sulfate or magnesium carbonate). The process is applicable to fatty acids comprising 2 to 36 carbons, or to fatty acids containing rings, and to all amino acids.

[0021] From this, a problem arises: to provide an improved amidation process, valid for all combinations of amino acids and fatty acids and characterized by a high conversion rate without the use of a "reaction foot" or dehydrating salts. A solution of the present invention is a process for preparing an amino acid N-acyl comprising the reaction of a fatty acid and an amino acid at a temperature of 165°C or higher for at least 1 hour, preferably at a temperature of 180°C or higher for a duration of between 1 and 10 hours.

[0022] The successful execution of the process does not depend on the nature of the amino acids or the starting fatty acids, and does not require a "starter" or the addition of aqueous solution. Furthermore, this process reduces the color of the final products, which are cream to orange rather than brown to black as in previous processes.

[0023] Depending on the case, the process according to the invention may have one or more of the following characteristics: The amino acid N-acyl is an N-acylated derivative of amino acids of formula (I): R1-C(=O)-Y-OH (I), in which R1-C(=O) represents an acyl radical, linear or branched, saturated or unsaturated, comprising from 2 to 36 carbon atoms and Y represents either a radical of formula (la): N(R3)-CH(R2)-C(=O) (la), in which R3 represents the hydrogen atom or the methyl radical, and R2 represents a hydrogen atom or an alkyl radical, or a radical of formula (Ib): in which R4 represents the hydrogen atom or the hydroxyl radical. The fatty acid has the formula (III): R1-C(=O)-OH (III), in which R1-C(=O) represents an acyl radical, linear or branched, saturated or unsaturated, comprising from 2 to 36 carbon atoms with at least one amino acid of formula (IIa): in which R3 represents the hydrogen atom or the methyl radical, and R2 represents a hydrogen atom or an alkyl radical, or of formula (IIb): in which R4 represents a hydrogen atom or a hydroxyl radical. The radical R2 represents a hydrogen atom or a radical selected from among the following radicals: methyl, isopropyl, isobutyl, 1-methylpropyl, benzyl, 3-aminopropyl, hydroxymethyl, 1-hydroxyethyl, thiomethyl, (2-methylthio)ethyl, 4-aminobutyl, 3-guanidinopropyl, 3-ureidopropyl, (1-aminocarbonyl)methyl, carboxymethyl, 2-carboxyethyl, 2-(aminocarbonyl)ethyl, 4-hydroxybenzyl, 3,4-dihydroxybenzyl, [1H-indol-3-yl]methyl, (1H-imidazol-4-yl)methyl. The process includes a step of simultaneously introducing the fatty acid and the amino acid into a reactor.The process comprises: a step a) in which the fatty acid is heated to a temperature of 165°C or higher; a step b) in which the amino acid in solid form is added, in one or more additions, at a temperature of 150°C or higher, to the fatty acid from step a) to obtain a mixture M1; and a step c) in which said mixture M1 is kept under mechanical stirring for at least one hour at a temperature of 165°C or higher to obtain an aqueous mixture M2 comprising the amino acid N-acyl. The molar ratio of the amino acid to the fatty acid is between 0.5 and 1.0. During step c), the alkalinity index of mixture M1 is measured until it reaches a value less than or equal to 0.2 milliequivalents per gram of mixture M1.The process comprises: a step a) in which the fatty acid is heated to a temperature of 165°C or higher; a step b) in which the amino acid in solid form is added, in one or more portions, at a temperature between 80°C and 120°C, to the fatty acid from step a) to obtain a mixture M1; a step c) in which said mixture M1 is heated to a temperature of 165°C or higher; and a step d) in which said mixture M1 is maintained under mechanical stirring for at least one hour at a temperature of 165°C or higher to obtain an aqueous mixture M2 comprising the amino acid N-acyl. During step d), the alkalinity index of mixture M1 is measured until it reaches a value less than or equal to 0.2 milliequivalents / gram of mixture M1.In the context of this invention, the term "alkalinity index" refers to the value resulting from a potentiometric titration of the anhydrous portion of the reaction medium. During this titration, the residual amine groups of the amino acid are titrated with a strong acid (perchloric acid), using an electrode adapted to determine the equivalence potential of the acid / base titration and the volume of acid present at the equivalence point. The "alkalinity index" is expressed as milliequivalents of acid added at the equivalence point per gram of sample titrated. In this case, it represents the molar equivalent of unreacted amine groups in the reaction medium. This measurement of the "alkalinity index" is a means of monitoring the progress of the reaction and the conversion of the amine groups of the amino acid.Step a) comprises a first substep of melting the fatty acid and a second substep of homogenizing the fatty acid. The process includes an additional step of isolating the amino acid N-acyl group from mixture M2. The process is carried out under a nitrogen atmosphere. The fatty acid is such that the linear or branched, saturated or unsaturated acyl radical R1-C(=O)-, constituting the fatty acid of formula (III), has from 6 to 36 carbons, preferably from 10 to 18 carbons, and even more preferably from 12 to 18 carbons.The amino acid is chosen from amino acids of formula (IIa) in which R3 represents the hydrogen atom and in which the radical R2 represents the hydrogen atom or a radical chosen from the radicals methyl, isopropyl, isobutyl, 1-methylpropyl, benzyl, 3-guanidinopropyl, [1H-indol-3-yl]methyl, (1H-imidazol-4-yl)methyl, 2-carboxyethyl, or from amino acids of formula (IIb) in which R3 represents the hydrogen atom and in which the radical R4 represents the hydrogen atom or the hydroxy radical.

[0024] The present invention also relates to a method for manufacturing a cosmetic composition comprising the preparation of an amino acid N-acyl as defined above.

[0025] An example of such a cosmetic composition is a topical cosmetic composition (C) comprising, by mass, 100% of: from 0.1% to 40% by mass, more particularly from 0.1% to 20% by mass, and even more particularly from 0.1% to 5% by mass of the mixture (M2) as defined above, and from 60% to 99.9% by mass, more particularly from 80% to 99.9%, and even more particularly from 95% to 99.9% by mass of a cosmetically acceptable medium.

[0026] The expression "for topical use" used in the definition of cosmetic composition for topical use (C) as defined above means that said composition is implemented by application to the skin, hair, scalp, lips or mucous membranes, whether by direct application in the case of a cosmetic or pharmaceutical composition or by indirect application, for example in the case of a personal hygiene product in the form of a textile or paper wipe or sanitary products intended to be in contact with the skin or mucous membranes.

[0027] The term "cosmetically acceptable," used in the definition of a cosmetic composition for topical use (C), means, according to Council Directive 76 / 768 / EEC of 27 July 1976, as amended by Directive 93 / 35 / EEC of 14 June 1993, any substance or preparation intended to be placed in contact with the various parts of the human body (epidermis, hair and scalp, nails, lips, and genital organs) or with the teeth and the mucous membranes of the mouth with a view exclusively and primarily to cleaning them, perfuming them, changing their appearance and / or correcting body odors and / or protecting them or keeping them in good condition. A cosmetically acceptable medium for these compositions may typically contain water, one or more cosmetically acceptable organic solvents, or a mixture of water and one or more organic solvents.Cosmetically acceptable solvents can be chosen in particular from polyhydric alcohols such as glycerol, diglycerol, glycerol oligomers, ethylene glycol, propylene glycol, hexylene glycol, diethylene glycol, xylitol, erythritol, sorbitol, or water-soluble alcohols.

[0028] The topical cosmetic composition (C) may be packaged in pressurized form in an aerosol device or a pump bottle, in a device with a perforated wall, such as a grid, or in a device with a rollerball applicator (known as a "roll-on"). When packaged in bottles, the composition (C) as defined above may be applied as a fine mist using mechanical or propellant pressurization devices. Propellants that may be used with composition (C) include hydrofluorinated compounds such as dichlorodifluoromethane, trichlorofluoromethane, difluorethane, isobutane, butane, and propane.

[0029] The topical cosmetic composition (C) as defined above may further include excipients and / or active ingredients commonly used in topical formulations, particularly cosmetic or pharmaceutical. The topical cosmetic composition (C) as defined above may further include one or more auxiliary compounds selected from among foaming and / or detergent surfactants, thickening and / or gelling surfactants, thickening and / or gelling agents, stabilizing agents, film-forming compounds, solvents and co-solvents, hydrotropic agents, plasticizers, opacifying agents, pearlescent agents, sequestering agents, chelating agents, antioxidants, perfumes, essential oils, preservatives, conditioning agents, deodorizing agents, and bleaching agents for hair and skin lightening.Active ingredients intended to provide a treatment and / or protective action on the skin or hair, sunscreens, mineral fillers or pigments, particles providing a visual effect or intended for the encapsulation of active ingredients, exfoliating particles, texturizing agents, optical brighteners, insect repellents.

[0030] Among the antioxidant agents that can be associated with the topical cosmetic composition (C) are ascorbic acid, glutathione, tartaric acid, oxalic acid, tetrasodium glutamate diacetate, vitamin E and its derivatives.

[0031] Among the water-soluble sequestering agents that can be associated with the topical cosmetic composition (C) are the salts of ethylenediamine tetraacetic acid (EDTA), such as the sodium salt of EDTA, the salts of diethylenetriamine pentacetic acid (DTPA), such as the sodium salts of DTPA, and acetyl glutamic acid (Dissolvine range).

[0032] Among the water-soluble colorants that can be associated with the topical cosmetic composition (C) are caramel, Yellow 5, Acid Blue 9 / Blue 1, Green 5, Green 3 / Fast Green FCF 3, Orange 4, Red 4 / Food Red 1, Yellow 6, Acid Red 33 / Food Red 12, Red 40, cochineal carmine (CI 15850, CI 75470), Ext. Violet 2, Red 6-7, Ferric Ferrocyanide, Ultramarines, Acid Yellow 3 / Yellow 10, Acid Blue 3, Yellow 10.

[0033] Among the water-soluble color-stabilizing agents that can be associated with the topical cosmetic composition (C) are Tris(tetramethyl hydroxypiperidinol) citrate, sodium benzotriazolyl butylphenol sulfonate, and benzotriazolyl dodecyl p-cresol.

[0034] Examples of foaming surfactants and / or detergents, possibly present in the topical cosmetic composition (C), include topically acceptable anionic, cationic, amphoteric or non-ionic foaming surfactants and / or detergents commonly used in this field of activity.

[0035] Among the anionic foaming and / or detergent surfactants that can be associated with the topical cosmetic composition (C), we can mention alkali metal salts, alkaline earth metal salts, ammonium salts, amine salts, amino alcohol salts of alkyl ether sulfates, alkyl sulfates, alkylamidoether sulfates, alkylarylpolyether sulfates, monoglyceride sulfates, alpha-olefin sulfonates, paraffin sulfonates, alkyl phosphates, alkyl ether phosphates, alkyl sulfonates, alkylamide sulfonates, alkylaryl sulfonates, alkyl carboxylates, alkylsulfosuccinates, alkyl ether sulfosuccinates, alkylamide sulfosuccinates, alkyl sulfoacetates, alkyl sarcosinates, acylisethionates, N-acyl taurates, acyl lactylates, N-acylated derivatives of amino acids, N-acylated derivatives of peptides, N-acylated derivatives of proteins, fatty acids.

[0036] Among the amphoteric foaming and / or detergent surfactants possibly present in the topical cosmetic composition (C), we can mention alkylbetaines, alkylamidobétaines, sultaines, alkylamidoalkylsulfobetaines, imidazoline derivatives, phosphobetaines, amphopolyacetates and amphopropionates.

[0037] Among the cationic foaming surfactants and / or detergents possibly present in the cosmetic composition for topical use (C), quaternary ammonium derivatives can be particularly mentioned.

[0038] Among the non-ionic foaming and / or detergent surfactants possibly present in the topical cosmetic composition (C), we can mention in particular alkylpolyglycosides having an aliphatic radical, linear or branched, saturated or unsaturated, and having 8 to 12 carbon atoms; castor oil derivatives, polysorbates, coconut amides, N-alkylamines. Examples of texturizing agents that may be present in the topical cosmetic composition (C) include N-acylated derivatives of amino acids, for example lauroyl lysine marketed under the name AMINOHOPE™ LL, octenyl starch succinate marketed under the name DRYFLO™, myristyl polyglucoside marketed under the name MONTANOV 14, cellulose fibers, cotton fibers, chitosan fibers, talc, sericite, mica, perlite.Examples of active ingredients that may be present in the topical cosmetic composition (C) include: Vitamins and their derivatives, for example, retinol (vitamin A) and its esters (retinyl palmitate for example), ascorbic acid (vitamin C) in salt form and its esters, sugar derivatives of ascorbic acid (for example ascorbyl glucoside), tocopherol (vitamin E) and its esters (for example tocopherol acetate), vitamins B3 or B10 (niacinamide and its derivatives); Compounds having a skin-lightening or depigmenting action, for example SEPIWHITE™< MSH, arbutin, kojic acid, hydroquinone, VEGEWHITE™< , GATULINE™< , SYNERLIGHT™< , BIOWHITE™< , PHYTOLIGHT™< , DERMALIGHT™< , CLARISKIN™< , MELASLOW™< , DERMAWHITE™< , ETHIOLINE, MELAREST™< , GIGAWHITE™< , ALBATINE™< , LUMISKIN™< ; Compounds with a soothing action such as SEPICALM™< S, allantoin, umbelliferous plant seed oil such as SEPIBLISS™<, and bisabolol;Anti-inflammatory agents such as Diclofenac™; Compounds with a moisturizing effect such as diglycerol, triglycerol, urea, hydroxyureas, glycerol glucoside, diglycerol glucoside, polyglyceryl glucosides, erythrityl glucoside, sorbityl glucoside, xylityl glucoside, the composition marketed under the brand name AQUAXYL™ containing xylityl glucoside, anhydroxylitol and xylitol; Compounds with a slimming or lipolytic effect such as caffeine or its derivatives, ADIPOSLIM™, ADIPOLESS™; Plant extracts rich in tannins, polyphenols and / or isoflavones, such as grape extracts, pine extracts, wine extracts, olive extracts; soy extracts, for example Raffermine™; wheat extracts, for example TENSINE™ or GLIADINE™; plant extracts rich in terpenes; freshwater or marine algae extracts;Marine extracts in general, such as corals; Compounds with antimicrobial or purifying action, for example LIPACIDE™< C8G, LIPACIDE™< UG, SEPICONTROL™< A5; OCTOPIROX™< or SENSIVA™< SC50; Compounds with energizing or stimulating properties, such as Physiogenyl™<, panthenol and its derivatives, such as SEPICAP™< MP; Anti-aging active ingredients, such as SEPILIFT™< DPHP, LIPACIDE™< PVB, SEPIVINOL™<, SEPIVITAL™<, MANOLIVA™<, PHYTO-AGE™<, TIMECODE™<; SURVICODE™<; Anti-photoaging agents; Agents that increase the synthesis of extracellular matrix components, for example collagen, elastins, glycosaminoglycans; Agents that act favorably on chemical cell communication, such as cytokines, or physical cell communication, such as integrins;Active ingredients that create a "warming" sensation on the skin, such as activators of cutaneous microcirculation (e.g., nicotinic acid derivatives) or products that create a "cooling" sensation on the skin (e.g., menthol and derivatives); Active ingredients that improve cutaneous microcirculation, for example, venotonics; draining active ingredients; decongestant active ingredients, for example, extracts of ginkgo biloba, ivy, horse chestnut, bamboo, butcher's broom, centella asiatica, fucus, rosemary, willow;Active ingredients acting as skin-tightening agents, for example, plant protein hydrolysates, marine hydrolysates such as laminaria extract hydrolysates, fish cartilage hydrolysates, marine elastin, the product marketed by SEPPIC under the brand name SESAFLASH™, collagen solutions. Skin-tanning or browning agents, for example, dihydroxyacetone, isatin, alloxan, ninhydrin, glyceraldehyde, mesotartaric aldehyde, glutaraldehyde, erythrulose.

[0039] Examples of deodorant agents that may be present in the topical cosmetic composition (C) include alkali silicates, zinc salts such as zinc sulfate, zinc gluconate, zinc chloride, zinc lactate; quaternary ammonium salts such as cetyltrimethylammonium salts, cetylpyridinium salts; Glycerol derivatives such as glycerol caprate, glycerol caprylate, polyglycerol caprate, 1,2-decanediol, 1,3-propanediol, salicylic acid, sodium bicarbonate, cyclodextrins, metallic zeolites, Triclosan™, aluminum bromohydrate, aluminum chlorohydrates, aluminum chloride, aluminum sulfate, aluminum zirconium chlorohydrates, aluminum zirconium trichlorohydrate, aluminum zirconium tetrachlorohydrate, aluminum zirconium pentachlorohydrate, aluminum zirconium octochlorohydrate, aluminum sulfate,Sodium aluminum lactate, aluminum hydrochloride and glycol complexes, such as aluminum hydrochloride and propylene glycol complex, aluminum dihydrochloride and propylene glycol complex, aluminum sesquihydrochloride and propylene glycol complex, aluminum hydrochloride and polyethylene glycol complex, aluminum dihydrochloride and polyethylene glycol complex, aluminum sesquihydrochloride and polyethylene glycol complex.

[0040] Examples of thickening or gelling agents that may be present in topical cosmetic compositions (C) include linear, branched, or cross-linked polyelectrolyte polymers, such as partially or totally salified acrylic acid homopolymer, partially or totally salified methacrylic acid homopolymer, partially or totally salified 2-methyl-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid (AMPS) homopolymer, acrylic acid and AMPS copolymers, acrylamide and AMPS copolymers, vinylpyrolidone and AMPS copolymers, AMPS and (2-hydroxyethyl) acrylate copolymers, AMPS and (2-hydroxyethyl) methacrylate copolymers, and copolymers of AMPS and hydroxyethylacrylamide, copolymers of AMPS and N,N-dimethyl acrylamide, copolymers of AMPS and tris(hydroxy-methyl)acrylamidomethane (THAM),copolymers of acrylic or methacrylic acid and (2-hydroxyethyl) acrylate, copolymers of acrylic or methacrylic acid and (2-hydroxyethyl) methacrylate, copolymers of acrylic or methacrylic acid and hydroxyethylacrylamide, copolymers of acrylic or methacrylic acid and THAM, copolymers of acrylic or methacrylic acid and N,N-dimethyl acrylamide, terpolymers of acrylic or methacrylic acid, AMPS and (2-hydroxyethyl) acrylate, terpolymers of acrylic or methacrylic acid, AMPS and (2-hydroxyethyl) methacrylate, terpolymers of acrylic or methacrylic acid, AMPS and THAM, terpolymers of acrylic or methacrylic acid, AMPS and N,N-dimethyl acrylamide, terpolymers of acrylic or methacrylic acid, AMPS and acrylamide,copolymers of acrylic acid or methacrylic acid and alkyl acrylates having a carbon chain of between four and thirty carbon atoms and more particularly between ten and thirty carbon atoms, copolymers of AMPS and alkyl acrylates having a carbon chain of between four and thirty carbon atoms and more particularly between ten and thirty carbon atoms, linear, branched or crosslinked terpolymers of at least one monomer having a strong acid function, free, partially salified or totally salified, with at least one neutral monomer, and at least one monomer of formula (VIII): CH2=C(R'3)-C(=O)-[CH2-CH2-O]n-R'4 (VIII) in which R'3 represents a hydrogen atom or a methyl radical,R' 4 represents a linear or branched alkyl radical comprising eight to thirty carbon atoms and n represents a number greater than or equal to one and less than or equal to fifty; Polyelectrolyte-type polymers, linear, branched, or cross-linked, which can be combined with topical cosmetic compositions (C), may be in the form of a solution, an aqueous suspension, a water-in-oil emulsion, an oil-in-water emulsion, or a powder, for example, products marketed under the names SIMULGEL™ EG, SIMULGEL™ EPG, SEPIGEL™ 305, SIMULGEL™ 600, SIMULGEL™ NS, SIMULGEL™ INS 100, SIMULGEL™ FL, SIMULGEL™ A, SIMULGEL™ SMS 88, SEPINOV™ EMT 10, SEPIPLUS™ 400, SEPIPLUS™ 265, SEPIPLUS ™< S, SEPIMAX ™< Zen, ARISTOFLEX ™< AVC, ARISTOFLEX ™< AVS, NOVEMER ™< EC-1, NOVEMER ™< EC 2, ARISTOFLEX ™< HMB, COSMEDIA ™< SP, FLOCARE ™< ET 25, FLOCARE ™< ET 75, FLOCARE ™< ET 26, FLOCARE ™< ET 30, FLOCARE ™< ET 58, FLOCARE ™< PSD 30,VISCOLAM ™< AT 64, VISCOLAM ™< AT 100; polysaccharides consisting solely of sugars, such as glucans or glucose homopolymers, glucomannoglucans, xyloglycans, galactomannans whose degree of substitution (DS) of the D-galactose units on the main D-mannose chain is between 0 and 1, and more particularly between 1 and 0.25, such as galactomannans from cassia gum (DS = 1 / 5), carob gum (DS = 1 / 4), tara gum (DS = 1 / 3), guar gum (DS = 1 / 2), fenugreek gum (DS = 1); polysaccharides composed of sugar derivatives, such as sulfated galactans, particularly carrageenans and agar; uronans, particularly algins, alginates, and pectins; heteropolymers of sugars and uronic acids, particularly xanthan gum, gellan gum, exudates of gum arabic and karaya gum; glucosaminoglycans; cellulose,Cellulose derivatives such as methylcellulose, ethylcellulose, hydroxypropyl cellulose, silicates, starch, hydrophilic starch derivatives, polyurethanes.

[0041] Examples of oils that may be present in the topical cosmetic composition (C) include mineral oils such as paraffin oil, petroleum jelly, isoparaffins or white mineral oils; oils of animal origin, such as squalene or squalane;vegetable oils, such as phytosqualane, sweet almond oil, coconut oil, castor oil, jojoba oil, olive oil, rapeseed oil, peanut oil, sunflower oil, wheat germ oil, corn germ oil, soybean oil, cottonseed oil, alfalfa oil, poppy oil, pumpkin seed oil, evening primrose oil, millet oil, barley oil, rye oil, safflower oil, candlenut oil, passionflower oil, hazelnut oil, palm oil, shea butter, apricot kernel oil, coriander seed oil, beechnut oil, tamanu oil, and sysymbrium oil, avocado oil, calendula oil, oils derived from flowers or vegetables, ethoxylated vegetable oils;synthetic oils such as fatty acid esters like butyl myristate, propyl myristate, isopropyl myristate, cetyl myristate, isopropyl palmitate, octyl palmitate, butyl stearate, hexadecyl stearate, isopropyl stearate, octyl stearate, isocetyl stearate, dodecyl oleate, hexyl laurate, propylene glycol dicaprylate, lanolic acid esters such as isopropyl lanolate, isocetyl lanolate, fatty acid monoglycerides, diglycerides and triglycerides such as glyceryl triheptanoate, alkylbenzoates, hydrogenated oils, poly(alpha-olefins), polyolefins such as poly(isobutane), synthetic isoalkanes such as isohexadecane, isododecane, perfluorinated oils;silicone oils such as dimethylpolysiloxanes, methylphenyl-polysiloxanes, amine-modified silicones, fatty acid-modified silicones, alcohol-modified silicones, alcohol and fatty acid-modified silicones, polyether-modified silicones, epoxy-modified silicones, fluorinated-modified silicones, cyclic silicones, and alkyl-modified silicones. For the purposes of this application, "oils" means compounds and / or mixtures of compounds that are insoluble in water and are liquid at a temperature of 25°C.

[0042] Examples of waxes that may be present in the topical cosmetic composition (C) include beeswax, carnauba wax, candelilla wax, ouricoury wax, Japanese wax, cork fiber wax, sugar cane wax, paraffin waxes, lignite waxes, microcrystalline waxes, lanolin wax; ozokerite; polyethylene wax; silicone waxes; vegetable waxes; fatty alcohols and fatty acids that are solid at room temperature; and glycerides that are solid at room temperature. For the purposes of this application, "waxes" means compounds and / or mixtures of compounds that are insoluble in water and are solid at a temperature of 45°C or higher.

[0043] Examples of non-ionic emulsifying surfactants that can be associated with topical cosmetic compositions (C) include fatty acid and sorbitol esters, such as products marketed under the names MONTANE™< 40, MONTANE™< 60, MONTANE™< 70, MONTANE™< 80 and MONTANE™< 85; compositions comprising glyceryl stearate and ethoxylated stearic acid with between five and one hundred and fifty moles of ethylene oxide, such as the composition comprising ethoxylated stearic acid with one hundred and thirty-five moles of ethylene oxide and glyceryl stearate marketed under the name SIMULSOL™< 165; mannitan esters; ethoxylated mannitan esters; sucrose esters; methyl glucoside esters;alkyl polyglycosides having an aliphatic radical, linear or branched, saturated or unsaturated, and having from fourteen to thirty-six carbon atoms, such as tetradecyl polyglucoside, hexadecyl polyglucoside, octadecyl polyglucoside, hexadecyl polyxyloside, octadecyl polyxyloside, eicosyl polyglucoside, dodecosyl polyglucoside, (2-octyl dodecyl) polyxyloside, (12-hydroxy stearyl) polyglucoside; compositions of linear or branched fatty alcohols, saturated or unsaturated, and comprising fourteen to thirty-six carbon atoms, and of alkyl polyglycosides as described above, for example compositions marketed under the brand names MONTANOV™< 68, MONTANOV™< 14, MONTANOV™< 82, MONTANOV™< 202, MONTANOV™< S, MONTANOV™< WO18, MONTANOV™< L, FLUIDANOV™< 20X and EASYNOV™< .;

[0044] Examples of agents protecting against ultraviolet radiation from the sun that may be present in the topical cosmetic composition (C) include pigments, organic sunscreens and inorganic sunscreens.

[0045] Examples of pigments used as a protective agent against ultraviolet radiation from the sun that may be present in the topical cosmetic composition (C) include titanium dioxide, brown iron oxides, yellow iron oxides, black iron oxides, or red iron oxides, or even pearlescent white or colored pigments such as Mica-Titanium.

[0046] Examples of organic sunscreens used as protective agents against ultraviolet radiation from the sun that may be present in topical cosmetic compositions (C) include: Those in the benzoic acid derivative family such as para-aminobenzoic acids (PABA), including monoglycerol esters of PABA, N,N-propoxy PABA ethyl esters, N,N-diethoxy PABA ethyl esters, N,N-dimethyl PABA ethyl esters, N,N-dimethyl PABA methyl esters, N,N-dimethyl PABA butyl esters; Those in the anthranilic acid derivative family such as homomenthyl-N-acetyl anthranilate; Those in the salicylic acid derivative family such as amyl salicylate, homomenthyl salicylate, ethylhexyl salicylate, phenyl salicylate, benzyl salicylate, p-isopropanolphenyl salicylate;Those in the cinnamic acid derivative family such as ethylhexyl cinnamate, ethyl-4-isopropyl cinnamate, methyl-2,5-diisopropyl cinnamate, p-methoxypropyl cinnamate, p-methoxyisopropyl cinnamate, p-methoxyisoamyl cinnamate, p-methoxyoctyl cinnamate (p-methoxy 2-ethylhexyl cinnamate), p-methoxy 2-ethoxyethyl cinnamate, p-methoxycyclohexyl cinnamate, ethyl-α-cyano-β-phenyl cinnamate, 2-ethylhexyl-α-cyano-β-phenyl cinnamate, glyceryl mono-2-ethylhexanoyl diparamethoxy cinnamate;Those in the benzophenone derivative family such as 2,4-dihydroxy benzophenone, 2,2'-dihydroxy 4-methoxy benzophenone, 2,2',4,4'-tetrahydroxy benzophenone, 2-hydroxy 4-methoxy benzophenone, 2-hydroxy 4-methoxy 4'-methyl benzophenone, 2-hydroxy 4-methoxy benzophenone-5-sulfonate, 4-phenyl benzophenone, 2-ethylhexyl 4'-phenyl benzophenone-2-carboxylate, 2-hydroxy 4-n-octyloxy benzophenone, 4-hydroxy 3-carboxy benzophenone; 3-(4'-methylbenzylidene) d,l-camphor, 3-(benzylidene)-d,l-camphor, benzalkonium methosulfate camphor; urocanic acid, ethyl urocanate; Those of the sulfonic acid derivative family such as 2-phenylbenzimidazole-5-sulfonic acid and its salts;the family of triazine derivatives such as hydroxyphenyl triazine, ethylhexyloxyhydroxyphenyl-4-methoxyphenyltriazine, 2,4,6-trianillino-(p-carbo-2'-ethylhexyl-1'-oxy) 1,3,5-triazine, 4,4-((6-(((1,1-dimethylethyl)amino)carbonypagel)phenyl)amino)-1,3,5-triazine-2,4-diyldiimino)bis-(2-ethylhexyl) benzoic acid ester, 2-phenyl-5-methylbenzoxazole, 2,2'-hydroxy-5-methylphenyl benzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl) benzotriazole, 2-(2'-hydroxy-5'-methylphenyl) benzotriazole; dibenzazine; dianisoylmethane, 4-methoxy-4"-t-butylbenzoylmethane; 5-(3,3-dimethyl-2-norbornylidene)-3-pentan-2-one;2-(4-diethylamino 2-hydroxy benzoyl) benzoic acid hexyl ester, 2,4-bis{[4-(2-ethylhexyloxy)-2-hydroxy] phenyl}-6-(4-methoxy phenyl) 1,3,5-triazine, 2,4,6-tris[4-(2-ethylhexyloxycarbonyl) anilino]-1,3,5-triazine, 2-ethylhexyl dimethoxybenzylidene dioxoimidazolidine propionate, the family of diphenyl acrylate derivatives such as 2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate, ethyl-2-cyano-3,3-diphenyl-2-propenoate; Those of the polysiloxane family such as benzylidene siloxane malonate.

[0047] Examples of inorganic sunscreens used as protective agents against the sun's ultraviolet radiation that may be present in topical cosmetic formulations (C) include: titanium dioxide, zinc oxide, cerium oxide, zirconium oxide, yellow, red, or black iron oxides, and chromium oxides. These mineral sunscreens may or may not be micronized, may or may not have undergone surface treatments, and may be presented as aqueous or oily pre-dispersions.

[0048] The following examples illustrate the invention without, however, limiting it.

[0049] Comparison between the process according to the invention (process 1) and the comparative processes, one of which is described in the document FR3066194 (process 2) and the other is a variant of process 2 distinguished by the absence of a reaction foot (process 3). As a reminder, process 2 described in document FR 3066194 is as follows: Loading the reactor with fatty acid of formula (III), melting and homogenizing under stirring at 80°C (clear medium). Addition of amino acid of formula (IIa) and / or formula (IIb) and the "starter of the reaction". Maintaining the temperature at 150°C with a nitrogen flow in the atmosphere. Shutdown and emptying under a nitrogen atmosphere.

[0050] The reaction foot is formed from the N-acyl of the amino acid that we want to synthesize and can come from the implementation of a Shotten Baumann process (involving a fatty acid chloride) or from a process resulting from direct amidation (involving a fatty acid of formula (III)). Process 3 is a variant of process 2, containing the same steps except for the addition of the "starter," which is not introduced into the reaction medium. Description of process 1 according to the invention: The quantity of fatty acid of formula (III), representing 0.5 to 1.0 molar equivalent, is introduced into a reactor equipped with a double jacket containing a heat transfer fluid, a mechanical stirrer fitted with an anchor or propeller-type stirring blade, and a water-cooled condenser. During the introduction of the fatty acid, the temperature is raised to 80°C to melt the fatty acid if necessary.

[0051] Subsequently, the temperature is raised to 150°C, and 1.0 molar equivalent of amino acid of formula (IIa) or formula (IIb), or a mixture of amino acids of formula (IIa) and / or formula (IIb), is introduced onto the stirred fatty acid as a solution or aqueous dispersion at 150°C. This introduction may be carried out all at once or in several fractions. The stirred reaction mixture is then heated to 180°C under a nitrogen atmosphere for a minimum of one hour. The progress of the reaction is monitored by measuring the "alkalinity index" of the reaction medium at regular intervals, and the reaction medium is gradually cooled when the alkalinity index of the reaction medium is less than or equal to 0.2 milliequivalents / gram of reaction medium.

[0052] The conversion rate is calculated as the ratio of the molar quantity of fatty acid that reacted to the molar quantity of fatty acid added, expressed as a percentage. The number of moles of fatty acid added is calculated based on the mass of fatty acids added. The number of moles of fatty acid that reacted is calculated based on the percentage of fatty acids remaining in the finished product. Taux de conversion = n moles acide gras réagi / n moles acide gras départ × 100 n moles of starting fatty acid = mass of fatty acid introduced / WW fatty acid % of fatty acid measured: Fatty acid determination is a quantitative determination measured against a standard solution, carried out by implementing a gas chromatography method.

[0053] The percentage areas of the peaks corresponding to the amino acid N-acyl were measured by implementing a qualitative method with a gas chromatography device, and were normalized to 100.

[0054] The following examples illustrate the invention without, however, limiting it. I- Examples of N-palmitoyl isoleucine preparation by the process according to the invention and comparative processes Example 1: Preparation of N-palmitoyl isoleucine by implementing process 1 according to the invention

[0055] 213.1 grams of palmitic acid (or hexadecanoic acid), equivalent to 0.6 molar units, are introduced into a two-liter reactor equipped with a double jacket containing a heat transfer fluid, a mechanical stirrer fitted with an anchor or propeller-type stirring blade, and a water-cooled condenser. During the introduction of the fatty acid, the temperature is raised to 80°C to melt the fatty acid if necessary.

[0056] Once the fatty acid is homogenized, the molten fatty acid is brought to a temperature of 150°C and then 181.7 grams of isoleucine, or 1 molar equivalent, are added.

[0057] The mixture is then heated to 180°C, with the alkalinity index of the reaction medium monitored by measuring it at regular intervals until it reaches or falls below 0.2 milliequivalents / gram of reaction medium. This threshold value was reached after three hours.

[0058] The reaction medium is gradually cooled and the reactor is then drained to obtain the LAA1 composition. Example 2: Preparation of N-palmitoyl isoleucine by implementing process 2

[0059] 213.1 grams of palmitic acid (or hexadecanoic acid), equivalent to 0.6 molar units, are introduced into a two-liter reactor equipped with a double jacket containing a heat transfer fluid, a mechanical stirrer fitted with an anchor or propeller-type stirring blade, and a water-cooled condenser. During the introduction of the fatty acid, the temperature is raised to 80°C to melt the fatty acid if necessary.

[0060] Once the fatty acid is homogenized, the molten fatty acid is brought to a temperature of 150°C and then an aqueous dispersion is added comprising 181.7 grams or 1 molar equivalent of isoleucine and an amount of 100.7 grams of N-palmitoyl isoleucine with 98% purity, previously obtained by a Schotten Bauman type process, i.e. a mass proportion of 25% ("reaction foot") of N-palmitoyl isoleucine in the reaction medium.

[0061] The mixture was then heated to 155°C, with the alkalinity index of the reaction medium monitored by measuring it at regular intervals until it was less than or equal to 0.2 milliequivalents / gram of reaction medium. This threshold value was reached after 12.5 hours.

[0062] The reaction medium is gradually cooled and the reactor is then drained to obtain the LAA11 composition. Example 3: Preparation of N-palmitoyl isoleucine by implementing process 3

[0063] The process described in example 2 is reproduced but without the addition of the quantity of "reaction foot" and the reaction temperature between the species is 150°C instead of 155°C, for a duration of 12h30, to obtain the composition LAA12. Example 4: Preparation of N-palmitoyl isoleucine by implementing process 3

[0064] The process described in example 3 is reproduced but with a reaction temperature between the species of 160°C instead of 150°C, for a duration of 3h00, to obtain the composition LAA13. Example 5: Preparation of N-palmitoyl isoleucine by implementing process 3

[0065] The process described in example 3 is reproduced but with a reaction temperature between the species of 160°C instead of 150°C, for a duration of 4h30, to obtain the composition LAA14. Example 6: Preparation of N-palmitoyl isoleucine by implementing process 3

[0066] The process described in Example 3 is reproduced but with a reaction temperature between the species of 160°C instead of 150°C, for a duration of 19.5 hours, to obtain the LAA15 composition. The operating conditions of the examples 1, 2, 3, 4, 5 and 6, and the analytical characteristics of the corresponding LAA1, LAA11, LAA12, LAA13, LAA14 and LAA15 compositions, are recorded in Table 1 below. [Table 1] Composition reference LAA11 LAA12 LAA1 LAA13 LAA14 LAA15 PROCESS 2 3 1 according to the invention 3 3 3 palmitic acid / isoleucine molar ratio 0,6 0,6 0,6 0,6 0,6 0,6 Reaction temperature 155°C 150°C 180°C 160°C 160°C 160°C Duration of maintenance at reaction temperature 12h30 18h30 3h00 3h00 4h30 19h30 Foot reaction 25% Without Without Without Without Without Analyses Appearance at 25°C Solid Brown Solid yellow Solid yellow Solid Cream Solid Beige Solid brown Alkalinity Index (milliequivalent / gram) 0,19 1,93 0,04 2,876 2,070 0,056 Residual palmitic acid content (% by mass) 11,1 28,5 10,5 40,2 36,6 9,6 Molar conversion rate Palmitic acid (%) 74 49,4 82 30,2 36,5 83,3 Residual isoleucine in % area / 34,3 / 40,1 37,0 / Di-isoleucine in % area / 0,2 3,9 / 0,2 2,7 Influence of the nature of the preparation process of compositions based on N-Palmitoyl Isoleucine.

[0067] Based on the fatty acid conversion rates, it is clear that using the foot at 150°C is necessary. Without it, the reaction occurs more rapidly and with a higher conversion rate, provided the temperature is increased to 180°C.

[0068] Process 1 according to the invention makes it possible to obtain a composition LAA1 comprising a low content of residual palmitic acid (10.5%), with a high rate of conversion of palmitic acid (82%), without introducing a "starter of reaction" and thus to improve the productivity of the process by limiting the cost of raw materials.

[0069] On the other hand, process 2 involving a "reaction foot" makes it possible to achieve a LAA11 composition comprising a low content of residual palmitic acid (10.5%) with a lower conversion rate (74%) than that measured in process 1 (82%), with a longer reaction time (12h30) than that of process 1 (3h00).

[0070] When process 3 is implemented to prepare compositions LAA13 and LAA14, with a reaction temperature of 160°C, the palmitic acid conversion rates are significantly lower (30.2% for LAA13 and 36.5% for LAA14) and the residual palmitic acid levels are significantly higher (40.2% for LAA13 and 36.6% for LAA14).

[0071] Process 3 allows obtaining a LAA15 composition with a high conversion rate (83.3%) and a low residual palmitic acid content (9.6%) when the holding time at 160°C is 19h30, which has the disadvantage of reducing productivity and obtaining a brown colour composition unsuitable for use in formulations intended for the cosmetic and pharmaceutical industries. II- Examples of the preparation of N-Undecylenoyl Phenylalanine by the process according to the invention and by the comparative process 2 Example 7: Preparation of N-undecylenoyl phenylalanine by implementing process 1 according to the invention

[0072] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 109.7 grams of undecylenoyl acid, the 181.7 grams of isoleucine with 121.7 grams of phenylalanine, to obtain the composition LAA2. Example 8: Preparation of N-undecylenoyl Phenylalanine by implementing comparative process 2

[0073] Example 2 is reproduced by replacing the 213.1 grams of palmitic acid with 40.5 grams of undecylenoyl acid, the 181.7 grams of isoleucine with 50.4 grams of phenylalanine, and the 100.7 grams of 98% purity N-palmitoyl isoleucine (reaction foot) with 27.0 grams of 98% purity N-undecylenoyl phenylalanine (reaction foot), to obtain the composition LAA21.

[0074] The operating conditions of examples 7 and 8, and the analytical characteristics of the corresponding LAA2 and LAA21 compositions, are recorded in Table 2 below. [Table 2] Composition reference LAA21 LAA2 PROCESS 2 1 according to the invention Undecylenoid Acid / Phenyl Alanine Molar Ratio 0,72 0,8 mass percentage of "reaction foot" 30% 0% Reaction temperature 155°C 180°C Duration of maintenance at reaction temperature 17h30 7h00 Analyses Appearance at 25°C Solid brown Solid Yellow Alkalinity Index (meq / g) 0,274 0,104 Residual undecylenoic acid content (mass %) 7,5 5,3 Molar conversion rate Undecylenic acid (%) 79 90 Phenylalanine in % area 5,7 nd Di-Phenylalanine in % area 6,9 4,4

[0075] Influence of the nature of the preparation process of compositions based on N-Undecenoyl Phenylalanine.

[0076] It is clear from examples 7 and 8 that process 1 according to the invention makes it possible to obtain a composition LAA2 with a low undecylenenoyl acid content (5.3%) and a high conversion rate of undecylenenoyl acid (90%). III- Examples of N-Palmitoyl Leucine preparation by the process according to the invention and by comparative process 3 Example 9: Preparation of N-palmitoyl leucine by implementing process 1 according to the invention

[0077] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 244.1 grams of palmitic acid, the 181.7 grams of isoleucine with 207.8 grams of leucine, to obtain the composition LAA3. Example 10: Preparation of N-palmitoyl Leucine by implementing comparative process 3

[0078] Example 9 is repeated with a reaction holding temperature of 150°C instead of 180°C, to obtain composition LAA31.

[0079] The operating conditions of examples 9 and 10, and the analytical characteristics of the corresponding LAA3 and LAA31 compositions, are recorded in Table 3 below. [Table 3] C16 Leucine Composition reference LAA31 LAA3 Process 3 1 according to the invention Palmitic acid / Leucine molar ratio 0,6 0,6 Reaction temperature 150°C 180°C Duration of maintenance at reaction temperature 25h00 10h00 Analyses Appearance at 25°C Solid brown Solid White Rosé Alkalinity Index (meq / g) 2,78 0,044 Residual Palmitic Acid Determination (% by mass) 34,5 7,7 Molar conversion rate of palmitic acid (%) 38,5 85,8 Residual leucine in % area 40,0 / % Fatty Acid Area 35,1 18,4 DI-Leucine % area 7,0 3,5 Influence of the nature of the preparation process of compositions based on N-Palmitoyl Leucine.

[0080] It is clear from examples 9 and 10 that process 1 according to the invention makes it possible to obtain a composition LAA3 with a low palmitic acid content (7.7%) and a high conversion rate of undecylenoyl acid (85.8%), and that the composition LAA21, obtained according to process 3, is characterized by a high residual palmitic acid content (34.5%) and a low conversion rate of palmitic acid (38.5%). IV- Examples of N-Palmitoyl PhenylAlanine preparation by the process according to the invention and by comparative process 3 Example 11: Preparation of N-palmitoyl PhenylAlanine by implementing process 1 according to the invention

[0081] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 142.0 grams of palmitic acid, the 181.7 grams of isoleucine with 184.6 grams of phenylalanine, to obtain the composition LAA4. Example 12: Preparation of N-palmitoyl PhenylAlanine by implementing comparative process 3

[0082] Example 11 is reproduced with a reaction holding temperature of 150°C instead of 180°C, to obtain composition LAA41.

[0083] The operating conditions of examples 11 and 12, and the analytical characteristics of the corresponding LAA4 and LAA41 compositions, are recorded in Table 4 below. [Table 4] Composition references LAA41 LAA4 Process 3 1 according to the invention Palmitic Acid / Phenylalanine molar ratio 0,7 0,5 Reaction temperature 150°C 180°C Duration of maintenance at reaction temperature 19h45 6h20 Analyses Appearance at 25°C Solid brown Solid, hard, yellow Alkalinity Index (milliequivalent / g) 1,902 0,02 Palmitic Acid Dosage (% by mass) 31,6 16,3 Molar conversion rate of palmitic acid (%) 41,4 64,8 Phenyl Alanine (as a percentage of area) 34,4 / % Fatty Acid Area 36,0 34,6 Di-Phenyl Alanine (as a percentage of area) 7,9 8,0 Influence of the nature of the process of preparing compositions based on Palmitoyl PhenylAlanine.

[0084] It is clear from examples 11 and 12 that process 1 according to the invention makes it possible to obtain a composition LAA4 with a lower palmitic acid content (16.3%) and a high palmitic acid conversion rate (64.8%), and that the composition LAA41, obtained according to process 3, is characterized by a higher residual palmitic acid content (31.6%) and a lower palmitic acid conversion rate (41.4%). V- Examples of N-Lauroyl Isoleucine preparation by the process according to the invention and by comparative process 3 Example 13: Preparation of N-lauroyl isoleucine by implementing process 1 according to the invention

[0085] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 140.0 grams of lauric acid, the 181.7 grams of isoleucine with 152.0 grams of isoleucine, to obtain the composition LAA5. Example 14: Preparation of N-lauroyl isoleucine by implementing comparative process 3

[0086] Example 13 is reproduced with a reaction holding temperature of 150 °C instead of 180 °C, to obtain composition LAA51.

[0087] The operating conditions of examples 13 and 14, and the analytical characteristics of the corresponding LAA5 and LAA51 compositions, are recorded in Table 5 below. [Table 5] Composition reference LAA51 LAA5 Process 3 1 according to the invention Fatty Acid / Isoleucine Equivalent 0,6 0,6 Reaction temperature 150°C 180°C Duration of maintaining the reaction temperature 15h00 4h30 Analyses Appearance at 25°C Brown paste Brown paste Alkalinity Index (meq / g) 1,356 0,017 Lauric acid dosage (%) 22,2 10,1 Molar conversion rate of lauric acid (%) 55,6 80,4 Residual isoleucine (as a percentage of area) 40,5 / % Fatty Acid Area 24,9 20,4 Di-Isoleucine (as a percentage of area) 3,4 2,3 Influence of the nature of the preparation process of N-Lauroyl Isoleucine-based compositions

[0088] It is clear from examples 13 and 14 that process 1 according to the invention makes it possible to obtain a composition LAA5 with a lower lauric acid content (10.1%) and a high lauric acid conversion rate (80.4%), and that the composition LAA51, obtained according to process 3, is characterized by a higher residual lauric acid content (22.2%) and a lower lauric acid conversion rate (55.6%). VI- Example of preparation of N-octanoyl leucine derivatives by the process according to the invention. Example 15: Preparation of N-octanoyl leucine by implementing process 1 according to the invention

[0089] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 214.7 grams of octanoic acid, the 181.7 grams of isoleucine with 244.5 grams of leucine, to obtain the composition LAA6.

[0090] The operating conditions of example 15, and the analytical characteristics of the corresponding LAA6 composition, are recorded in Table 6 below. [Table 6] Reference LAA6 Process 1 according to the invention Palmitic acid / Proline molar ratio 0,8 Reaction temperature 180°C Duration of maintaining the reaction temperature 4h45 Appearance at 25°C Yellow paste Alkalinity Index (meq / g) 0,026 Residual octanoic acid content (%) 20,3 Molar conversion rate of octanoic acid (%) 59,8 Residual leucine (as a percentage of area) / Di-Leucine (as a percentage of area) 11,9 Composition and analytical characteristics of the LAA6 composition obtained by process 1 according to the invention.

[0091] Example 15, by implementing process 1 according to the invention, makes it possible to obtain a LAA6 composition with a low octanoic acid content (20.1%) and a high octanoic acid conversion rate (59.8%). VII- Examples of preparation of N-acylated derivatives of proline by the process according to the invention. Example 16: Preparation of N-palmitoyl Proline by implementing process 1 according to the invention

[0092] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 95.8... grams of palmitic acid, the 181.7 grams of isoleucine with 71.6 grams of proline, and by gradually introducing the proline onto the fatty acid, to obtain the composition LAA7. Example 17: Preparation of N-stearoyl Proline by implementing process 1 according to the invention

[0093] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 79.2 grams of stearic acid, the 181.7 grams of isoleucine with 53.5 grams of proline, and by gradually introducing the proline onto the fatty acid, to obtain the composition LAA8. Example 18: Preparation of N-Oleyl Proline by implementing process 1 according to the invention

[0094] We reproduce example 1 by replacing the 213.1 grams of palmitic acid with 102.4 grams of oleic acid, the 181.7 grams of isoleucine with 69.3 grams of proline, and by gradually introducing the proline onto the fatty acid, to obtain the composition LAA9.

[0095] The operating conditions of examples 16, 17 and 18, and the analytical characteristics of the corresponding compositions LAA7, LAA8 and LAA9, are recorded in Table 7 below. [Table 7] Reference LAA7 LAA8 LAA9 Process 1 according to the invention 1 according to the invention 1 according to the invention Palmitic acid / Proline molar ratio 0,6 - - Stearic acid / Proline molar ratio - 0,6 - Oleic acid / Proline molar ratio - - 0,6 Reaction temperature 180°C 180°C 180°C Duration of proline introduction 1h45 1h30 1h15 Duration of maintaining the reaction temperature 1h00 1h00 1h00 Appearance at 25°C Yellow paste Solid yellow Yellow liquid Alkalinity Index (meq / g) 0,015 0,011 0,015 Residual palmitic acid content (%) 16,9 - - Residual stearic acid content (%) - 18,3 - Residual oleic acid content (%) - - 13,5 Molar conversion rate Palmitic acid (%) 72,4 - - Molar conversion rate of stearic acid (%) - 71,3 - Molar conversion rate of oleic acid (%) - - 78,8 Residual proline (as a percentage of area) / - - Di-Proline (as a percentage of area) 13,7 12,9 13,0 Composition and analytical characteristics of compositions LAA7, LAA8 and LAA9 obtained by process 1 according to the invention.

[0096] In examples 16, 17 and 18, the implementation of process 1 according to the invention makes it possible to obtain compositions with a low content of residual fatty acids (16.9% palmitic acid in LAA7, 18.3% stearic acid in LAA8 and 13.5% oleic acid in LAA9) and with a high fatty acid conversion rate (72.4% for palmitic acid in LAA7, 71.3% for stearic acid in LAA8 and 78.8% for oleic acid in LAA9).

Claims

1. Method for preparing an N-acylamino acid, comprising the reaction of a fatty acid and an amino acid at a temperature greater than or equal to 165°C for at least 1 h.

2. Method according to Claim 1, characterized in that the N-acylamino acid is an N-acyl derivative of amino acids of formula (I):         R1-C(=O) -Y-OH     (I), in which R1-C(=O) represents a linear or branched, saturated or unsaturated acyl radical containing from 2 to 36 carbon atoms and Y represents either a radical of formula (Ia): N(R3)-CH(R2)-C(=O) (Ia), in which R3 represents the hydrogen atom or the methyl radical and R2 represents a hydrogen atom or an alkyl radical, i.e. a radical of formula (Ib): in which R4 represents the hydrogen atom or the hydroxyl radical.

3. Method according to one of Claims 1 and 2, characterized in that the fatty acid is of formula (III):         R1-C(=O)-OH     (III), in which R1-C(=O) represents a linear or branched, saturated or unsaturated acyl radical containing from 2 to 36 carbon atoms with at least one amino acid of formula (IIa): in which R3 represents the hydrogen atom or the methyl radical and R2 represents a hydrogen atom or an alkyl radical, or of formula (IIb): in which R4 represents a hydrogen atom or a hydroxyl radical.

4. Method according to one of Claims 2 and 3, characterized in that radical R2 represents a hydrogen atom or a radical selected from methyl, isopropyl, isobutyl, 1-methylpropyl, benzyl, 3-aminopropyl, hydroxymethyl, 1-hydroxyethyl, thiomethyl, (2-methylthio)ethyl, 4-aminobutyl, 3-guanidinopropyl, 3-ureidopropyl, (1-aminocarbonyl)methyl, carboxymethyl, 2-carboxyethyl, 2-(aminocarbonyl)ethyl, 4-hydroxybenzyl, 3,4-dihydroxybenzyl, [1H-indol-3-yl]methyl and (1H-imidazol-4-yl)methyl.

5. Method according to one of Claims 1 to 4, characterized in that it comprises a step of simultaneously introducing into a reactor the fatty acid and the amino acid.

6. Method according to any one of Claims 1 to 5, characterized in that the molar ratio between the amino acid and the fatty acid is between 0.5 and 1.0.

7. Method according to one of Claims 1 to 6, characterized in that it is performed under a nitrogen atmosphere.

8. Method according to one of Claims 1 to 7, comprising: - a step a) in which the fatty acid is brought to a temperature greater than or equal to 165°C, - a step b) in which the amino acid in solid form is poured in one or more portions, at a temperature greater than or equal to 150°C, onto the fatty acid obtained from step a) so as to obtain a mixture M1, and - a step c) in which said mixture M1 is maintained under mechanical stirring for at least a period of one hour and at a temperature greater than or equal to 165°C so as to obtain an aqueous mixture M2 comprising the N-acylamino acid.

9. Method according to Claim 8, characterized in that, during step c), the base number of mixture M1 is measured until a value of less than or equal to 0.2 milliequivalents / gram of mixture M1 is attained.

10. Method according to one of Claims 1 to 7, comprising: - a step a) in which the fatty acid is brought to a temperature greater than or equal to 165°C, - a step b) in which the amino acid in solid form is poured in one or more portions, at a temperature of between 80°C and 120°C, onto the fatty acid obtained from step a) so as to obtain a mixture M1, - a step c) in which said mixture M1 is heated to a temperature greater than or equal to 165°C, and - a step d) in which said mixture M1 is maintained under mechanical stirring for at least one hour and at a temperature greater than or equal to 165°C so as to obtain an aqueous mixture M2 comprising the N-acylamino acid.

11. Method according to Claim 10, characterized in that, during step d), the base number of mixture M1 is measured until a value of less than or equal to 0.2 milliequivalents / gram of mixture M1 is attained.

12. Method according to one of Claims 8 to 11, characterized in that step a) comprises a first substep of melting the fatty acid and a second substep of homogenizing the fatty acid.

13. Method according to one of Claims 8 to 12, characterized in that it comprises an additional step of isolating the N-acylamino acid from mixture M2.

14. Method for producing a cosmetic composition comprising the preparation of an N-acylamino acid as defined in one of Claims 1 to 13.

15. Method according to Claim 14, comprising the preparation of an N-acylamino acid as defined in one of Claims 8 to 12 and in which the cosmetic composition is a cosmetic composition for topical use (C) comprising, per 100% of its weight: - from 0.1% to 40% by weight of the mixture (M2) and - from 60% to 99.9% by weight of a cosmetically acceptable medium.