WO1993001791A1

WO1993001791A1 - Azeotropic blend of propyl 2-hydroxy thioglycolate and ethyl 1-methyl 2-hydroxy thioglycolate, process for its preparation and use thereof in a process for achieving a permanent change in hair waviness

Info

Publication number: WO1993001791A1
Application number: PCT/FR1992/000728
Authority: WO
Inventors: Alex Junino; Gérard Malle; Charles Vayssie
Original assignee: L'oreal
Priority date: 1991-07-23
Filing date: 1992-07-23
Publication date: 1993-02-04
Also published as: FR2679448B1; FR2679448A1

Abstract

Azeotropic blend of thioglycolic acid 1,2-propanediol esters consisting of two thirds propyl 2-hydroxy thioglycolate of the formula (I): HS-CH2-COO-CH2-CHOH-CH3, and one third ethyl 1-methyl 2-hydroxy thioglycolate of the formula (II): HS-CH2-COO-CH(CH3)-CH2OH. Cosmetic use for achieving a permanent change in hair waviness.

Description

Azeotropic mixture of 2-hydroxypropyl thioglycolate and 2-hydroxyethyl methyl thioglycolate, process for obtaining it and its use in a process for permanent hair deformation.

The subject of the present invention is an azetropic mixture of 1,2-propanediol esters of thioglycolic acid, its process for obtaining and its use, as reducing agent, in a process for permanent deformation of the hair.

The conventional technique for carrying out permanent deformation of the hair consists, firstly, in opening the disulphide bonds of the keratin (cystine) using a composition containing a reducing agent (reduction step), then , after having preferably rinsed the hair, to reconstitute in a second time, said disulfide bonds by applying, to the hair under tension, an oxidizing composition (oxidation step also called fixing) so as to give the hair the desired shape . This technique makes it possible indifferently to carry out either the waving of the hair or their straightening or their straightening.

The compositions for carrying out the first stage of a perming operation are generally in the form of lotions, creams, gels or powders to be diluted in a liquid support, and contain, as reducing agent, preferably a thiol .

Among the latter, those commonly used are thioglycolic acid and thiolactic acid or a mixture of these acids, as well as their esters such as, for example, glycerol monothioglycolate, or glycol.

These reducing agents are particularly effective in reducing the disulfide bonds of keratin, in particular thioglycolic acid which is. generally considered to be the benchmark permanent product. However, it has been found that thioglycolic acid. had to be used in a sufficiently basic medium (pH ^* , 8.5) if one wanted to obtain a satisfactory crimp.

Glycerol monothioglycolate partially overcomes this drawback insofar as it is possible to obtain optimum crimping at pH 8.5, preferably at a pH between 6 and 8. However, in this pH zone, the crimp obtained with glycerol monothioglycolate remains - .—

significantly lower than that obtained with thioglycolic acid, in particular in the form of ammonium thioglycolate, at a much more basic pH.

After various studies, we have now found that it was possible to remedy the drawbacks of known reducing agents by using a well-defined azeotropic mixture of propanediol-1,2 monoesters of thioglycolic acid.

Indeed, this azeotropic mixture makes it possible, at the same molar concentration, to obtain not only a crimp greater than that obtained with glycerol monothioglycolate but also a crimp practically equivalent to that obtained at alkaline pH with thioglycolic acid.

It has also been found that the condition of the hair treated with the azeotropic mixture according to the invention was very satisfactory from the cosmetic point of view.

The subject of the present invention is therefore, as a new industrial product, an azeotropic mixture of 1,2-propanediol esters of thioglycolic acid, the latter consisting of 2/3 of 2-hydroxypropyl thioglycolate of formula:

HS-CH -C00-CH -CHOH-CK (I) and 1/3 of 2-methyl-1-hydroxyethyl thioglycolate of formula: HS-CH -C00-CH (CH) -CH OH (II)

2 3 z.

These proportions are indifferently molar or by weight insofar as these two esters (I) and (II) have the same molecular mass. The present invention also relates to the process for preparing the azeotropic mixture as defined above. This process consists in reacting thioglycolic acid with propanediol-1,2, without catalyst, by distilling the water formed as the reaction progresses.

The reaction is preferably carried out under an inert atmosphere in the presence of an excess of 1,2-propanediol in order to avoid the formation of the diester which has the major drawback of being insoluble in water.

In practice, two equivalents of 1,2-propanediol have been found to be sufficient. The reaction temperature is generally between 80 and 170 ° C, and preferably between 100 and 150 ° C to allow the elimination by distillation, of the water formed, under normal pressure, without degradation. It is also possible to facilitate the removal of water by azeotropy, and in this case, a conventional solvent is used such as, for example, toluene or xylene or else dichloroethane. When the reaction is complete, distillation is carried out under reduced pressure so as to obtain the azeotropic mixture according to the invention. The vacuum is preferably between 2 and 30 hPa because under these conditions, the composition of the azeotropic mixture according to the invention (proportion of 2/3 of (I) to 1/3 of (II)) remains constant.

The boiling point of the azeotropic mixture depends on the vacuum applied. By way of example, the boiling temperature is approximately 137-143 ° C at 26.6 hPa and approximately 106-115 ° C at 5.32 hPa.

The azeotropic mixture according to the invention also forms an azeotropic with propanediol-1,2, which makes it possible to obtain it either pure or optionally in solution in propanediol-1,2.

It should also be noted that quite unexpectedly and surprisingly, the proportion of the esters (I) and (II) of the azeotropic mixture according to the invention remains constant, that is to say 2/3 of (I) and 1 / 3 of (II) whatever the content of 1,2-propanediol.

The azeotropic mixture according to the invention can also be prepared by transesterification of an ester of thioglycolic acid with an equivalent of 1,2-propanediol, without an acid catalyst.

Particularly preferred thioglycolic acid esters are ethyl thioglycolate and methyl thioglycolate. The transesterification reaction is preferably carried out under an inert atmosphere and at one. temperature above the boiling point of the released ethanol or methanol, so as to facilitate their elimination under normal pressure. A co-solvent can also be used by forming an azeotrope with methanol or ethanol so as to facilitate their elimination. Among the preferred solvents, mention may in particular be made of 1,2-dichloroethane, N, N-dimethyl formamide or toluene. In practice, an equivalent of 1,2-propanediol is sufficient, but it can of course be used in excess if it is desired to increase the reaction rate. After the end of the reaction, a distillation is carried out so as to obtain the azeotropic mixture according to the invention in the proportions of 2/3 of (I) and 1/3 of (II).

The present invention also relates to a reducing composition for the first time of a permanent hair deformation operation containing, in a suitable cosmetic vehicle, as a reducing agent, the azeotropic mixture according to the invention. In the compositions according to the invention, the azeotropic mixture is generally present at a concentration of between 2 and 30% and preferably between 5 and 20% by weight relative to the total weight of the reducing composition. The pH of the composition is preferably between 4 and 8 and more particularly between 6 and 8 and is obtained using an alkaline agent such as, for example, ammonia, monoethanolamine, diethanolamine, triethanolamine, an alkali or ammonium carbonate or bicarbonate, an alkali hydroxide or using an acidifying agent such as for example hydrochloric acid, acetic acid, lactic acid, oxalic acid, boric acid, citric acid or phosphoric acid, or alternatively by means of buffers such as, for example, mono and dipotassium phosphate and ammonium acid carbonate.

The reducing composition may also contain other known reducing agents such as for example thioglycolic acid, glycerol or glycol monothioglycolate, cysteamine and its C -C acyl derivatives such as N-acé ylcystéamine or N- propionylcystéamine, cysteine, N-acetylcysteine, N-mercaptoalkylamides of sugars, such as N- (2-mercapto-ethyl) gluconamide, ^ -mercaptopropionique acid and its o _n derivatives, thiolactic acid, thiomalique, pantetheine, thioglycerol, sulfites and bisulfites of an alkali or alkaline earth metal, the N- (mercaptoalkyl) u> -hydroxyalkylamides described in patent application EP 354 835, the N-mono or N, N-dialkylroercapto 4-butyramides described in patent application EP 368 763, and the 5 a inomercaptoalkylamides described in patent application EP 403 267.

According to a preferred embodiment, the reducing composition also contains a surfactant of non-ionic, anionic, cationic or aephoteric type and among these mention may be made of alkyl sulfates, alkylbenzenesulfates, alkyl ether sulfates, alkyl sulfonates, 0 salts of quaternary ammonium, alkylbetaines, oxyethylenated alkylphenols, alkanolamides of fatty acids, esters of oxyethylenated fatty acids and other nonionic surfactants of the hydroxypropylether type.

When the reducing composition contains at least one agent ₅ surfactant, it is generally present at a maximum concentration of 30% by weight, but preferably between 0.5 and 10% based on the total weight of the reducing composition . In order to improve the cosmetic properties of the hair or to attenuate or avoid its degradation, the reducing composition may also contain a treating agent of cationic, anionic, nonionic or amphoteric nature. Among the particularly preferred treating agents, mention may in particular be made of those described in French patents No. 2,598,613, and No. 2,470,596. It is also possible to use, as treating agents, volatile or non-linear or cyclic silicones and their mixtures, polydimethylsiloxanes, quaternized polyorganosiloxanes such as those described in French patent application No. 2,535,730, polyorganosiloxanes with modified aminoalkyl groups. by alkoxycarbonylalkyl groups such as those described in US Pat. polydimethyl -siloxane polyalkylbetaine copolymer described in British Patent No. 2,197,352, organo polysiloxanes modified with mercapto or mercaptoalkyl groups such as those described in French Patent No. 1,530,369 and in European Patent Application No. 295,780 , as well as silanes such as stearoxytrimethylsilane.

The reducing composition may also contain other treating ingredients such as a basic inoacids (such as lysine, arginia) or acids (such as glutamic acid, aspartic acid), peptides and their derivatives, protein hydrolysates, waxes, bulking and penetrating agents or for enhancing the effectiveness of the reducing agent such as the SiO 2 / PDMS mixture

(polydimethylsiloxane), dimethylisosorbitol, urea and its derivatives, pyrrolidone, N-alkyl-pyrrolidones, thiamorpholino e, alkylene glycol or dialkylene glycol alkyl ethers such as for example propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monoethyl ether and diethylene glycol monoethyl ether, ^{C -} C alkanediols, such as for example 1,2-propanediol and 1,2-butanediol, 2-imidazolidinone as well as other compounds such as fatty alcohols, lanolin derivatives, active ingredients such as panthothenic acid, fall arrest agents, dandruff agents, thickeners, suspending agents, sequestering agents, opacifying agents, dyes, sun filters as well as perfumes and preservatives.

The reducing composition according to the invention is essentially in aqueous form, in particular in the form of a thickened or non-thickened lotion, a cream or a gel.

The reducing composition according to the invention can also be of the exothermic type, that is to say causing a certain heating during application to the hair, which brings pleasure to the person who undergoes the first time of the perm. or straightening. The reducing composition according to the invention can also contain a solvent such as for example ethanol, propanol, or isopropanol or also glycerol at a maximum concentration of 20% relative to the total weight of the composition.

Since the azeotropic mixture according to the invention is not very stable in an aqueous medium, it is preferable to produce the composition at the time of use by mixing the various ingredients.

In order to be able to produce the reducing composition, the ingredients are therefore packaged in several parts, the azeotropic mixture always being in an anhydrous medium. The pH regulating agent is generally present in the part containing the aqueous medium.

Cosmetic adjuvants can be present either in the aqueous phase or in the anhydrous phase provided of course that the azeotropic mixture remains in a completely anhydrous medium and that the compounds are compatible with each other.

The vehicle for the compositions according to the invention is preferably water or an aqueous-alcoholic solution of a lower alcohol such as ethanol, isopropanol or butanol.

When the compositions are intended for a hair straightening or straightening operation, the reducing composition is preferably in the form of a cream so as to keep the hair as straight as possible. These creams are produced in the form of "heavy" emulsions, for example based on glyceryl stearate, glycol stearate, self-emulsifying waxes, fatty alcohols, etc. We can also use liquids or gels containing thickening agents such as polymers or copolymers carboxyvinyls which "stick" the hair and keep it in the smooth position during the exposure time.

The compositions according to the invention can also be in so-called "self-neutralizing" or even "self-regulated" form and in this case, the azeotropic mixture according to the invention is associated with at least one disulfide is known for its use in a reducing composition for self-neutralizing perm either derived from the azeotropic mixture according to the invention and therefore corresponding to the following three compounds of formula (III), (IV) and (V):

- | -S-CH ₂ - COO-CH -CHOH-CH (III)

(IV)

S-CH -COO-CH -CHOH-CH

2 2 3 (V)

S-CH -COO-CH (CH) -CH OH

Among the known disulfides, mention may in particular be made of dithioglycolic acid, dithioglycerol, N, N'-diacetyl-cystamine, cystine, pantethine, disulphides of N- (mercaptoalkyl) "J-hydroxyalkylamides described in the application for Patent EP 354,835, the disulphides of N-mono or N, N-dialkylmercapto 4-butyramides described in patent application EP 368,763 and the disulphides of aminomercaptoalkylamides described in patent application EP 403,267. In self-neutralizing compositions , the disulfide is generally present in a molar ratio of 0.5 to 2.5 and preferably 1 to 2 relative to the azeotropic mixture of the compounds (I) and (II).

The disulphides of formula (III), (IV) and (V) are obtained by oxidation of the azeotropic mixture of the compounds (I) and (II), either in air, or by using known oxidants such as, for example hydrogen peroxide possibly in the presence of metal salts such as for example ferrous salts.

The present invention also relates to a process for permanent deformation of the hair, consisting, in a first step, in reducing the disulfide bonds of keratin by applying, for approximately 5 to 60 minutes, a reducing composition as defined above. then in a second step to reform said links by application of an oxidizing composition or optionally allowing the oxygen in the air to act.

The present invention also relates to a method of waving the hair in which a reducing composition as defined above is applied to wet hair previously rolled on rollers having from 4 to 20 mm in diameter, the composition possibly being applied as the hair is rolled up; the reducing composition is then left to act for a time of 5 to 60 min. preferably 5 to 30 min. at a temperature which may be between 20 and 55 ° ^C. , then rinsed then abundantly and after which an oxidizing composition is applied to the coiled hair, making it possible to reform the disulfide bonds of the keratin, for an exposure time of 2 to 10 minutes. After removing the rollers, rinse the hair thoroughly. The oxidation or oxidizing composition is of the type commonly used and contains, as oxidizing agent, hydrogen peroxide, an alkali bromate, a persalt, a polythionate or a mixture of alkali bromate and parsley.

The concentration of hydrogen peroxide can vary from 1 to 20 volumes and preferably from 1 to 10, the concentration of alkali bromate from 2 to 12% and that of parsley from 0.1 to 15% by weight relative to the total weight of the oxidizing composition. The pH of the oxidizing composition is generally between 2 and 8 but preferably between 3 and 6. The hydrogen peroxide can be stabilized for example by phenacetin, acetanilide, mono or trisodium phosphates or by hydroxy sulfate -8 quinoline. Oxidation can be immediate or delayed.

The present invention also relates to a hair straightening or straightening process in which a reducing composition according to the invention is applied to the hair, then the hair is subjected to mechanical deformation making it possible to fix them in their new shape, by a hair straightening operation with a wide tooth comb, with the back of a comb or by hand. After an exposure time of 5 to 60 min., In particular from 5 to 30 min., A further smoothing is then carried out, then the product is rinsed thoroughly and the oxidizing or fixing composition is applied, which is left to act for a period of 2 to 10 min. approximately then rinse the hair thoroughly. We will now give, by way of illustration and without any limiting character, examples of preparation of the azeotropic mixture according to the invention as well as examples of reducing compositions according to the invention and their use in a process for permanent deformation of the hair.

PREPARATION EXAMPLES

EXAMPLE 1 Preparation of the azeotropic mixture consisting of 2/3 of 2-hydroxypropyl thiogl colate (I) and 1/3 of 2-hydroxy thioglycolate methyl-1-ethyl (II) by direct esterification.

a) Without co-solvent

Heated for 7 hours at 140-150 ° C., under an argon atmosphere, a mixture of 456.6 g (4.96 moles) of thioglycolic acid and 754.4 g (9.92 moles) of propanediol-1, 2 while distilling off the water formed.

The residual water and part of the excess 1,2-propanediol are then distilled under the vacuum of a water pump (bp. < ^* 110 ° C).

We then proceed to the distillate itself under a vacuum of about 5.32 hPa, collecting:

- the fraction 76-105 ^c C (218.7 g) whose weight composition determined by assaying thiol and CPG is as follows: ester (I) 73 g

108.6 g ester (II) 35.6 g J propanediol-1.2 110.1 g

- the fraction 106-115 ° C (444.6 g of colorless liquid) containing only the azeotropic mixture of the two esters in the ratio 2/1. The thiol assay (I 0.1N). GPC analysis and C NMR spectrum are consistent. Elementary analysis: C. ₀ H ₂₀ 0, S ₂

(Fraction: 106-115 ° C / 5.32 hPa)

b) With a co-solvent

Heated for 6 hours under reflux and under an argon atmosphere, a solution of 92 g (1 mole) of thioglycolic acid, 113 cm ³ (1.5 moles) of propanediol-1,2 and 150 cm ³ of dichloro-1 , 2 ethane by collecting the water formed using a Dean-Stark apparatus.

Then distilled under the vacuum of the water pump and collected 69.4 g of colorless liquid of boiling point 137-143 ° C under

26.6 hPa.

13 The NMR spectrum C corresponds to the mixture (I) / (II): 2/1.

EXAMPLE 2 Preparation of jnélanjξe azeotrope consti.tu.e_de 2/3 of 2-hydroxy propyl thioglycolate (I) and 1/3 of hydroxy-2 methyl-1 methyl-1 thioglycolate by transesterification.

A solution of 60 g (0.5 mole) of ethyl thioglycolate and 76 g (0.5 mole) of propanediol-1,2 is heated for 3 hours at 120 ° C., under an inert atmosphere, while distilling the ethanol formed. .

It is then purified by distillation under the vacuum of a water pump to collect 31.5 g of colorless liquid with a boiling point 140-143 ° C at 27.9 hPa.

13 The C NMR spectrum is consistent. Elementary analysis: C _lf .E_ _n 0, S „

C% HZ 0% S% Calculated 39.98 6.71 31.96 21.35 Found 40.02 6.71 32.12 21.53

EXAMPLE 3 Preparation of the mixture of disulphides (III), (IV) and (V).

To a solution of 15 g (0.1 mole) of the azeotropic mixture (I) / (II) obtained according to example 1 or 2 in 100 cm ³ of tetrahydrofuran, 5.1 cm ³ (0, 05 mol) of 30% hydrogen peroxide and stirred at room temperature.

The transformation is complete after 1 hour of reaction (TLC and thiol assay). After evaporation of the solvent and drying under vacuum at 40 ^o C, 14.1 g of colorless to very pale yellow liquid are obtained.

By ¹³ C NMR DMSO dg, capillary GPC DB1 and GC / MS coupling, the presence of the 2 symmetrical disulfides (III) and (IV) and of the mixed disulfide (V) is demonstrated.

Elementary analysis: C, „H,„ 0.S „

10 18 6 2

COMPOSITION EXAMPLES

EXAMPLE A

According to the invention, a reducing composition for permanent deformation of the hair is prepared by proceeding as follows:

First of all, solution (a) is prepared: - Azeotropic mixture (I) / (II) 15 g

- Propylene glycol . ^'' 7.8 g Solution (b) is then prepared:

- Tégobétaine HS sold by the company GOLDSCHMIDT 1.3 g

- Triethanola ine 2.4 g

- Perfume qs - Demineralized water qs 77.2 g

After mixing solution (a) with solution (b), 100 g of reducing composition having a pH of 7.0 are obtained.

This reducing composition is applied to wet hair, previously wound on curlers, and left to act for 20 minutes at room temperature. Then rinse thoroughly with water and then apply the following oxidizing composition:

- Hydrogen peroxide at 200 volumes 4.8 g

- Stabilizer 0.2 g - Oleic alcohol with 20 moles of ethylene oxide 1.5 g

- Citric acid qs pH 3

- Demineralized water qs 100 g

The oxidizing composition is left to act for 10 minutes, rinsed thoroughly with water and then the curlers are removed.

After drying under a helmet, we see that the hair has beautiful curls with a good degree of curl.

* *

Using the same procedure as described above, the hair was permanently deformed using the reducing and oxidizing compositions of examples B to E below:

EXAMPLE B:

1) REDUCING COMPOSITION Solution (a):

- Azeotropic mixture (I) / (II) 7.5 g

- Glycerol monothioglycolate 8.3 g - Glycerin 3.9 g Solution (b):

- Oleocetyl dimethylammonium chloride 1.4 g

- Acid ammonium carbonate 3.5 g

- Perfume qs

- Demineralized water qs 80.3 g

100 g of solution having a pH of 7.1 are obtained. 2) OXIDIZING COMPOSITION

- Hydrogen peroxide at 200 volumes 4.8 g

- Stabilizers: 8-hydroxyquinoline sulfate and phenacetin ... 0.06 g

- Citric acid qs pH 3

- Demineralized water qs 100 g

EXAMPLE C

1) REDUCING COMPOSITION

Solution (a):

- Azeotropic mixture (I) / (II) 7.5 g

- Propylene glycol 7.8 g

Solution (b):

- Cysteamine hydrochloride 5.6 g

- Tegobetaine KS sold by the company GOLDSCHMIDT 1.3 g

- Triethanolami e 2.1 g

- Perfume qs

- Demineralized water qs 84.7 g

100 g of solution with a pH of 7.0 are obtained.

2) OXIDIZING COMPOSITION

- Bromate of. sodium 8 g

- Triethanolamine qs pH 7.5

- Onosodium phosphate monohydrate 0.3 g

- Trisodium phosphate 0.5 g

- Demineralized water qs 100 g EXAMPLE D

1) REDUCING COMPOSITION Solution (a)

- Azeotropic mixture (I) / (II) 7.5 g - Propylene glycol 7.8 g

Solution (b)

- N-acetylcysteamine 5.9 g

- Tegobetaine HS sold by the company GOLDSCHMIDT 1.3 g - Triethanolamine 1.7 g

- Perfume qs

- Demineralized water qs 84.7 g

100 g of solution having a pH of 6.9 are obtained.

2) OXIDIZING COMPOSITION

The same oxidizing composition is used as that described in Example A.

EXAMPLE E 1) REDUCING COMPOSITION Solution (a)

- Azeotropic mixture (I) / (II) 7.5 g

- N-propionylcysteamine 5.9 g

- 7.8 g polypropylene glycol

Solution (b)

- Tegobetaine HS sold by the company GOLDSCHMIDT 1, 3 g

- Triethanolamine 1, 7 g

- Perfume qs - Demineralized water qs 78.8 g

100 g of solution having a pH of 6.9 are obtained.

2) OXIDIZING COMPOSITION The same oxidizing composition is used as that described in Example B.

Claims

1. Azeotropic mixture of 1,2-propanediol esters of thioglycolic acid characterized in that it consists of 2/3 of 2-hydroxypropyl thioglycolate of formula:

HS-CH ₂ -COO-CH ₂ -CHOH-CH ₃ (I) and 1/3 of 2-methyl-1-methylthioglycolate of formula:

HS-CH ₂ -COO-CH (CH ₃ ) -CH ₂ OH (II).

2. Azeotropic mixture according to claim 1, characterized in that its boiling point under vacuum of around 5.32 hPa is between 106 and 115 ° C or between 137 and 143 ° C under a vacuum of about 26 , 6 hPa.

3. A process for preparing the azeotropic mixture according to claims 1 and 2, characterized in that it consists in reacting thioglycolic acid with propanediol-1,2, without catalyst, by distilling the water formed as and as it is formed.

4. Method according to claim 3, characterized in that two equivalents of propanediol-1,2 are reacted for one equivalent of thioglycolic acid.

5. Method according to claims 3 and 4, characterized in that the reaction temperature is between 100 and 150 ° C.

6. Cosmetic composition for the first stage of a permanent hair deformation operation, characterized in that it contains, in a suitable cosmetic vehicle, as reducing agent, an azeotropic mixture of propanediol-1 esters , 2 of thioglycolic acid as claimed in claims 1 and 2.

7. Composition according to Claim 6, characterized in that the azeotropic mixture is present at a concentration of between 2 and

30% and preferably between 5 and 20% by weight relative to the total weight of the composition.

8. Composition according to any one of claims 6 and 7, characterized in that it has a pK of between 4 and 8 and preferably between 6 and 8.

9. Composition according to Claim 8, characterized in that the pH is obtained using an alkaline agent such as ammonia, monoethanolamine, diethanolamine, triethanolamine, an alkali or ammonium carbonate or bicarbonate , an alkali hydroxide or using an acidifying agent such as hydrochloric acid, acetic acid, acid lactic, oxalic acid, boric acid, citric acid or phosphoric acid.

10. Composition according to any one of claims 6 to 9, characterized in that it also contains at least one other reducing agent chosen from: thioglycolic acid, glycerol or glycol monothioglycolate, cysteamine and its acyl derivatives C, -C ,, la

1 4 cysteine, N-acetylcysteine, N- (mercapto-alkylamide) of sugars, β-mercaptopropionic acid, thiolactic acid, thiomalic acid, pantethine, thioglycerol, a sulfite or a bisulfite an alkali or alkaline earth metal, the N- (mercaptoalkyl) u) -hydroxyalkylamides and the N-mono or N; N-dialkyl mercapto-4 butyramides.

11. Composition according to any one of claims 6 to 10, characterized in that it contains, in addition, at least one cationic polymer, a softening agent, a protein hydrolyzate, a wax, an opacifying agent, a perfume. , a dye, a nonionic surfactant, an alcohol, a treating agent or even a penetrating agent.

12. Composition according to any one of claims 6 to 11, characterized in that it also contains at least one disulfide, the composition being of the self-neutralizing type.

13. Composition according to claim 12, characterized in that the disulfide is dithioglycoliqυe acid, dithioglycerol, N, N'-diacetyl cystamine, cystine, panthetine, an N- (mercaptoalkyl) "- hydroxy disulfide alkylamide, an N-mono or N, N-dialkylmercapto 4-butyramide disulfide or an ino-mercaptoalkylamide disulfide.

14. Composition according to claim 12, characterized in that the disulfide derives from the azeotropic mixture according to claims 1 and 2 and corresponds to the following three compounds (III), (IV) and (V):

(III)

(IV)

S-CH ₂ -C00-CH ₂ CH0H-CH _{3 (γ)}

S-CH ₂ -C00-CH (CH ₃ ) -CH ₂ 0H

15. Composition according to any one of claims 12 to 14, characterized in that the disulfide is present in a proportion molar with respect to the azeotropic mixture according to claims 1 and 12 ranging from 0.5 to 2.5 and preferably from 1 to 2.

16. A method of permanent hair deformation consisting, in a first step, in reducing the disulfide bonds of keratin by application of a reducing composition, then in a second step, in reforming said bonds by application of an oxidizing composition, characterized in that the reduction step is carried out using a reducing cosmetic composition as claimed in any one of claims 6 to 11.

17. The method of claim 16, characterized in that the reducing composition is left to act for a time between 5 and 60 minutes.