Hydroxyl derivatives of benzaldehyde for coloring keratin fibres in the absence of oxidizing agent

Abstract

The invention discloses the use of hydroxyl derivatives of benzaldehyde for coloring keratin fibres without an oxidizing agent. These derivatives are of the type which correspond to the formula: ##STR1## in which R denotes a linear or branched lower alkyl group which is optionally substituted by one or two OH groups, n is equal to 1, 2 or 3, m is equal to 0, 1 or 2 and the sum n+m is equal to 2 or 3.

Description

DESCRIPTION

The present invention relates to the use of hydroxyl derivatives of benzaldehyde for colouring keratin fibres, as well as colouring processes and dyeing compositions in which these compounds are used.

Certain benzaldehyde derivatives have already been used in hair dyeing as oxidation dyestuffs, that is to say as compounds which only lead to coloured derivatives on oxidation by means of oxidising reagents, such as hydrogen peroxide or per-salts.

Thus, a dyeing process has been proposed using protocatechuic aldehyde, the shade being developed by means of inorganic oxidising agents chosen from alkali metal or ammonium iodates, periodates and persulphates.

We have now discovered that, surprisingly, a specific class of benzaldehydes makes it possible to colour keratin fibres, and in particular human hair, directly, without using an oxidising agent.

When they are used in this way, these compounds give rise to dyes having a good resistance to light, washing, adverse weather conditions and perspiration.

Some of these compounds are particularly useful for obtaining colorations in yellow shades.

The present invention thus relates to the use of these hydroxyl derivatives of benzaldehyde for colouring keratin fibres and in particular human hair.

The benzaldehyde derivatives used for colouring keratin fibres according to the present invention correspond to the general formula (I): ##STR2## in which R denotes a linear or branched lower alkyl group, preferably having 1 to 4 carbon atoms, which is optionally substituted by one or two hydroxyl groups, n is equal to 1, 2 or 3, m is equal to 0, 1 or 2 such that the sum n+m is equal to 2 or 3, with the proviso that if m is equal to 0 and n is equal to 2 or 3, the OH groups occupy the following positions of the ring:

______________________________________2 3 4 5 6______________________________________ OH OHOH OH OH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OH______________________________________ and if m and n both denote 1, the substituents occupy the following positions of the ring: ______________________________________2 3 4 5 6______________________________________OH OROR OH OH OR OH OROH OROH OCH.sub.2 CH.sub.2 OHOH ##STR3##OH OC.sub.2 H.sub.5______________________________________ or their bisulphite adducts.

The alkyl groups which are more particularly preferred are methyl or ethyl. The expression "bi-sulphite adduct" is to be understood as meaning the adduct resulting from the addition of one equivalent of an alkali metal bisulphite, such as sodium bisulphite or potassium bisulphite, to one equivalent of the hydroxyl derivative of benzaldehyde.

The compounds which are more particularly preferred according to the invention are those corresponding to the formula (I) in which the substituents having the meanings indicated in Table I occupy the positions also shown in Table I.

TABLE I______________________________________CompoundNo. 2 3 4 5 6______________________________________1 OH OH2 OH OH3 OH OH4 OH OH5 OH OH OH6 OH OH OH7 OH OH OH8 OH OH OH9 OH OH OH10 OH OCH.sub.311 OCH.sub.3 OH12 OH OCH.sub.313 OH OCH.sub.314 OH OC.sub.2 H.sub.515 OH OC.sub.2 H.sub.516 OH OH OCH.sub.317 OH OH OCH.sub.318 OH OH OCH.sub.319 OH OCH.sub.3 OH20 OH OH OCH.sub.321 OH OCH.sub.3 OH22 OH OCH.sub.3 OH23 OH OH OCH.sub.324 OH OCH.sub.3 OH25 OH OH OCH.sub.326 OH OH OCH.sub.327 OH OCH.sub.3 OH28 OCH.sub.3 OH OH29 OH OH OCH.sub.330 OCH.sub. 3 OH OH31 OH OCH.sub.3 OH32 OH OC.sub.2 H.sub.5 OH33 OH OH OC.sub.2 H.sub.534 OH OCH.sub.3 OCH.sub.335 OCH.sub.3 OH OCH.sub.336 OH OCH.sub.3 OCH.sub.337 OCH.sub.3 OH OCH.sub.338 OH OCH.sub.3 OCH.sub.339 OH OCH.sub.3 OCH.sub.340 OH OCH.sub.3 OCH.sub.341 OH OCH.sub.3 OCH.sub.342 OCH.sub.3 OH OCH.sub.343 OCH.sub.3 OH OCH.sub.344 OH OCH.sub.3 OCH.sub.345 OH OCH.sub.3 OCH.sub.346 OCH.sub.3 OCH.sub.3 OH47 OCH.sub.3 OH OCH.sub.348 OCH.sub.3 OH OCH.sub.349 OH OCH.sub.2 CH.sub.2 OH50 OH ##STR4##______________________________________

The process for colouring keratin fibres, and in particular human hair, according to the invention is characterised in that at least one composition containing, in a cosmetically acceptable medium, a dyestuff corresponding to the formula (I) above is applied to the said fibres, without an oxidising agent.

Although the process can be carried out at pH values of, say, 2 to 11, which are normally used in cosmetics, a preferred embodiment of the invention consists in carrying out the coloration in an acid medium.

Amongst the preferred dyestuffs used in this embodiment of the invention, there may be mentioned the dyestuffs of the formula (I) in which the substituents have the meanings indicated in Table II and occupy the positions of the benzene ring which are also shown in this table.

TABLE II______________________________________2 3 4 5 6______________________________________ OH OHOH OHOH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OH OCH.sub.3OH OH OCH.sub.3OH OH OCH.sub.3OH OCH.sub.3 OHOH OH OCH.sub.3OH OCH.sub.3 OHOH OCH.sub.3 OHOH OH OCH.sub.3OH OCH.sub.3 OH OH OH OCH.sub.3______________________________________

It is also possible to carry out the process in an alkaline medium, and the most remarkable results can be obtained with the dyestuffs corresponding to the formula (I) in which the substituents have the meanings indicated in Table III and occupy the positions of the benzene ring which are indicated in this table.

TABLE III______________________________________2 3 4 5 6______________________________________ OH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OCH.sub.3 OCH.sub.3OCH.sub.3 OH OCH.sub.3 OH OCH.sub.3 OCH.sub.3 OCH.sub.3 OH OCH.sub.3______________________________________

A dyeing process giving particularly valuable results consists in using the benzaldehyde derivatives corresponding to the general formula (I) indicated above, in powder form, mixing them with other solids, such as clay, talc or plant-based fillers, the whole being mixed with a liquid just before application to the hair. According to this embodiment of the invention, a poultice based on the benzaldehyde derivatives is applied to the keratin fibres and in particular human hair, it is left on the hair for, say, 5 to 60 minutes, and the hair is rinsed and dried.

The hair can also be coloured in accordance with processes comprising several steps, at least one of which consists in applying a dyestuff of the formula (I).

The dyeing compositions according to the invention are essentially characterised in that they contain, in a cosmetically acceptable medium, at least one of the derivatives corresponding to the formula (I) indicated above, as a dyestuff.

The compositions which are more particularly preferred according to the invention are those containing a benzaldehyde derivative corresponding to the formula (II) ##STR5## in which R, n and m have the meanings indicated above, n+m being equal to 3, or the compounds of the formula (III) ##STR6## in which the OH groups occupy the 2,6- or 3,5-positions.

The compositions according to the invention generally contain the compounds corresponding to the abovementioned formulae in an amount from 0.05 to 10% by weight and in particular from 0.1 to 5% by weight.

The cosmetically acceptable medium is typically aqueous and its pH is generally 2 to 11, it can be adjusted to the desired value by means of alkalising agents, such as ammonia, alkali metal carbonates, alkanolamines, such as mono-, di- or tri-ethanolamine, or alkylamines, or with acidifying agents, such as hydrochloric acid, sulphuric acid and citric acid.

The dyeing compositions according to the invention can also contain anionic, cationic, non-ionic and/or amphoteric surface-active agents or mixtures thereof. Amongst the surface-active agents which are more particularly preferred, there may be mentioned soaps, alkylbenzenesulphonates, alkylnaphthalenesulphonates, sulphates, ether-sulphates and sulphonates of fatty alcohols, quaternary ammonium salts, such as trimethylcetylammonium bromide and cetylpyridinium bromide, fatty acid diethanolamides, polyoxyethyleneated or polyglycerolated acids, alcohols and amides and polyoxyethyleneated or polyglycerolated alkylphenols. The surface-active agents are typically present in the compositions according to the invention in proportions of 0.1 to 55% by weight and preferably 1 to 40% by weight, relative to the total weight of the composition.

These compositions can also contain organic solvents for solubilising compounds which would not otherwise be sufficiently soluble in water. Amongst these solvents, examples which may be mentioned are lower alkanols, such as ethanol and isopropanol, glycerol, glycols or glycol ethers, such as ethylene glycol monobutyl ether, ethylene glycol, propylene glycol, and diethylene glycol monoethyl ether and monomethyl ether, and also analogous products or mixtures thereof. These solvents are preferably present in proportions from 1 to 50% by weight and more particularly from 3 to 30% by weight, relative to the total weight of the composition. The compositions can also contain anionic, non-ionic, cationic or amphoteric polymers, suitably in proportions from 0.1 to 5% by weight.

The compositions according to the invention can be thickened, preferably with sodium alginate, gum arabic or cellulose derivatives, such as methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose and carboxymethylcellulose, or various polymers serving this purpose, in particular acrylic acid derivatives. It is also possible to use inorganic thickeners, such as bentonite. These thickeners are preferably present in proportions of 0.5 to 5% by weight and in particular 0.5 to 3% by weight, relative to the total weight of the composition.

Antioxidants, such as sodium sulphite, thioglycolic acid, sodium bisulphite, ascorbic acid and hydroquinone, can also be included in the compositions according to the invention. These antioxidants are advantageously present in the composition in proportions of 0.05 to 1.5% by weight, relative to the total weight of the composition. It is of course possible to add to the compositions according to the invention any other adjuvants normally used in hair-dyeing compositions, and in particular penetrating agents, sequestering agents, buffers and perfumes.

It is self-evident that the compositions according to the invention can contain other direct dyestuffs, more particularly anthraquinone dyestuffs, azo dyestuffs, nitro benzene derivatives, indophenols, indamines and indoanilines.

The dyeing compositions according to the invention can be presented in various forms, such as liquids, creams, gels or any other form suitable for dyeing the hair. In particular, they can be packaged in aerosol flasks in the presence of a propellant.

Presentation in the form of a poultice constitutes a particularly preferred embodiment of the invention. In this case, the benzaldehyde derivatives used according to the invention are prepared in the form of a powder which is stable on storage and are incorporated into a solid medium. The term "poultice" is to be understood as meaning a product composed of powders, flours or starchy or mucilaginous substances, mixed with a liquid.

The powders can consist of, for example, insoluble substances, such as silicas, powdered plants, clays, and plants powdered after solvent extraction of their active principles. The liquid can be water and/or solvents, such as alcohols, glycols and oils. The viscosity which is generally obtained after mixing is suitably from 100 to 9,000 cps. A particularly preferred embodiment of the invention consists in using the benzaldehyde derivatives of the formula (I), and more particularly: 2,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde and 4-hydroxy-3,5-dimethoxybenzaldehyde, at the same time as other natural dyestuffs, so as to prepare a dyeing composition for keratin fibres, and preferably for human hair, which is based on natural substances. Natural dyestuffs which may be mentioned more particularly for this purpose are: lawsone, juglone, indigo and the plants or extracts in which these dyestuffs are present.

These compositions can be used as indicated above in hair-dyeing processes carried out in several stages, one step of the process consisting in applying at least one composition of the present invention.

The following Examples further illustrate the present invention.

EXAMPLE 1

The following composition is prepared:

______________________________________2,3,4-trihydroxybenzaldehyde 1 gethylglycol 10 gwater q.s.p. 100 g______________________________________

Hair swatches containing 90% of white hair are dyed with an application time of 30 minutes.

The swatches are rinsed and dried. A very intense yellow-green coloration is obtained.

EXAMPLES 2 TO 10

On replacing the 2,3,4-trihydroxybenzaldehyde by the hydroxyl derivatives of benzaldehyde which are indicated in the following Table IV, the composition containing the amount of ethylglycol also recorded in this table, the colorations shown in the last column of Table IV are obtained.

TABLE IV______________________________________ Ethyl- glycol Coloration obtainedExample (g) Dyestuff on 90% white hair______________________________________2 10 2,4-dihydroxy- moderately intense benzaldehyde yellow-green3 10 3,4-dihydroxy- fairly intense benzaldehyde yellow-green4 20 2,4,6-trihydroxy- intense yellow- benzaldehyde orange5 10 3,4,5-trihydroxy- intense yellow- benzaldehyde green6 10 3-hydroxy-4- light yellow-green methoxybenzaldehyde7 40 2-hydroxy-4,6- very light dimethoxybenzaldehyde yellow-green8 10 4-hydroxy-3,5- fairly intense dimethoxybenzaldehyde yellow-green9 10 2,5-dihydroxy-3- intense yellow- methoxybenzaldehyde orange10 10 3,4-dihydroxy-5- fairly intense methoxybenzaldehyde yellow-green______________________________________

EXAMPLE 11

The following dyeing composition is prepared:

______________________________________3,4-dihydroxybenzaldehyde 2 gvinylpyrrolidone/crotonic acid (90/10) 1copolymer 1.8 gvinylpyrrolidone/vinyl acetate (60/40)copolymer 0.4 g96.degree. strength ethyl alcohol q.s.p. 50.degree. alcoholic strengthtriethanolamine q.s.p. pH 6water q.s.p. 100 g______________________________________

When applied to light blond hair, this wavesetting lotion imparts a slight golden sheen to the hair after drying.

EXAMPLE 12

On adding 0.03 g of 1-N-(.delta.-aminopropyl)-aminoanthraquinone hydrochloride to the composition of Example 11, it imparts a light coppery blond shade to light blond hair.

EXAMPLE 13

The following composition is prepared:

______________________________________2-hydroxy-5-methoxybenzaldehyde 0.3 g3,4-dihydroxy-5-methoxybenzaldehyde 0.3 g1-(4'-nitrophenylazo)-2-methyl-4-(di-.beta.-hydroxyethylamino)-benzene (Disperse Red 17) 0.4 gN--(2',6'-dimethyl-4'-amino-5'-methoxyphenyl)-2,6-dimethyl-1,4-benzoquinone-imine 0.05 gvinylpyrrolidone/vinyl acetate (60/40)copolymer 0.5 gquaternised polyvinylpyrrolidone sold underthe name Gafquat 734 by Gaf 0.4 gtetradecyltrimethylammonium bromide 0.2 g96.degree. strength ethyl alcohol q.s.p. 50.degree. alcoholic strengthcitric acid q.s.p. pH 6water q.s.p. 100 g______________________________________

This composition constitutes a wavesetting lotion, which is applied to natural or coloured, chestnut hair.

The hair possesses a mahogany sheen after drying.

EXAMPLE 14

The following composition is prepared:

______________________________________2,4-dihydroxybenzaldehyde 1.5 gcetyl alcohol 17 gcetyl/stearyl alcohol containing 15 mols ofethylene oxide, sold under the name MergitalCS 15/E by Henkel 6 gOleyl alcohol sold under the name Ocenol HD80/85 by Henkel 3 gcitric acid q.s.p. pH 3water q.s.p. 100 g______________________________________

This cream is applied to natural or coloured, chestnut hair for 20 minutes.

After rinsing, the hair is shampooed and dried.

The hair then possesses a golden sheen.

EXAMPLE 15

The following dyeing composition is prepared:

______________________________________3,5-dimethoxy-4-hydroxybenzaldehyde 0.9 g4-methoxy-3-hydroxybenzaldehyde 0.5 g4-N--methylamino-1-N--(.gamma.-aminopropyl)-amino-anthraquinone hydrochloride 0.025 gsynthetic linear C.sub.13 -C.sub.15 fatty alcoholcontaining 2.8 mols of ethylene oxide, soldunder the name Ukanil 25 by PCUK 3 gsynthetic linear C.sub.9 -C.sub.11 fatty alcoholcontaining 6 mols of ethylene oxide, soldunder the name Ukanil 43 by PCUK 2 gtetradecyltrimethylammonium bromide 1.5 gethylglycol 10 gtriethanolamine q.s.p. pH 5water q.s.p. 100 g______________________________________

This foaming lotion is applied for fiteen minutes to hair having an unattractive red sheen.

After rinsing and drying, this red sheen has disappeared or has been greatly toned down.

EXAMPLE 16

The following dyeing composition is prepared:

______________________________________3,4-dihydroxy-5-methoxybenzaldehyde 0.35 gN.sub.1 --methyl-N.sub.4 --methyl-N.sub.4 --.beta.-hydroxyethyl-2-nitro-para-phenylenediamine 0.45 g50/50 mixture of cetyl alcohol and stearylalcohol, sold under the name lanette wax Oby Henkel 20 gcopra monoethanolamide 5 g20% pure ammonium lauryl-sulphate sold underthe name Sipon LA 30 by Henkel 10 g2-amino-2-methylpropanol q.s.p. pH 8.5water q.s.p. 100 g______________________________________

This composition, which is in the form of a cream, is applied for 30 minutes to a natural deep blond head of hair which is unsensitised and possesses a significant percentage of white hair.

The colour of the hair after shampooing and drying is revived to its natural shade and the white hair is covered in the same tint.

EXAMPLE 17

The following dyeing composition is prepared:

______________________________________3,4,5-trihydroxybenzaldehyde 0.8 gstandard methylene green BZ, Fluka (CI BasicGreen 5) 0.011 g1-amino-4-N--methylamino-2-nitrobenzene 0.44 gsodium salt of sulphated oxyethyleneatedalkanol - 0.6 to 0.65 meq (g) - sold underthe name Sadipan 8533 by Lever 25 gdiethanolamide of coconut fatty acid 5 gbutylglycol 1 gcitric acid q.s.p. pH 6water q.s.p. 100 g______________________________________

This colouring shampoo can be applied to deep blond or light chestnut hair.

After an application time of 15 minutes and after rinsing and drying, it imparts an attractive mahogany-brown shade to the hair.

EXAMPLE 18

The following dyeing composition is prepared:

______________________________________2,5-dihydroxy-3-methoxybenzaldehyde 1.2 g2-N--.beta.-hydroxyethylamino-5-hydroxynitrobenzene 0.2 gsynthetic linear C.sub.13 -C.sub.15 fatty alcohol con-taining 2.8 mols of ethylene oxide, sold underthe name Ukanil 25 by PCUK 3 gsynthetic linear C.sub.9 -C.sub.11 fatty alcohol con-taining 6 mols of ethylene oxide, sold underthe name Ukanil 43 by PCUK 2 gtetradecyltrimethylammonium bromide 1.5 gethylglycol 10 gtriethanolamine q.s.p. pH 5water q.s.p. 100 g______________________________________

This slightly foaming lotion is applied to hair which is chestnut to light chestnut.

After an application time of 15 minutes and after rinsing and drying, a head of hair possessing a coppery sheen is obtained.

EXAMPLE 19

The following dyeing composition is prepared:

______________________________________2,3,4-trihydroxybenzaldehyde 0.2 g1-amino-4-N--methylamino-2-nitrobenzene 0.2 g2-amino-5-hydroxynitrobenzene 0.1 g2-N--.beta.-hydroxyethylamino-5-methoxynitrobenzene 0.1 gCI Basic Blue 99 0.05 goxyethyleneated nonylphenol containing 4 molsof ethylene oxide, sold under the nameSinnopal NP 4 by Henkel 11 goxyethyleneated nonylphenol containing 9 molsof ethylene oxide, sold under the nameSinnopal NP 9 by Henkel 11 gpropylene glycol 5.5 gabsolute ethyl alcohol 4 gammonia q.s.p. pH 7.5water q.s.p. 100 g______________________________________

This gel is applied to blond hair for 30 minutes.

After shampooing and drying, a particularly attractive yellow-brown sheen is obtained if the hair has been slightly sensitised beforehand by perming.

EXAMPLE 20

The following composition is prepared:

______________________________________3,4-dihydroxybenzaldehyde 1.5 glawsone 0.1 gpowdered chestnut leaves q.s.p. 100 g______________________________________

This powder is mixed with four times its weight of warm water at the time of use.

The poultice obtained is then applied to a light blond head of hair for 20 minutes and then carefully removed. After shampooing and drying, the hair is embellished with a delicate golden sheen.

EXAMPLE 21

The following composition is prepared:

______________________________________4-hydroxy-3,5-dimethoxybenzaldehyde 2 g2,3-dihydroxybenzaldehyde 3 g2-N--.beta.-hydroxyethylamino-5-hydroxynitrobenzene 0.8 gwheat flour 10 grye flour 10 gfeedstuff-quality maize cobs q.s.p. 100 g______________________________________

Five times the weight of warm water is added to this powder at the time of use and the whole is mixed.

The poultice obtained is applied to a light chestnut head of hair. The sheen obtained after shampooing and drying is a coppery sheen.

Claims

1. Process for colouring keratin fibres in the absence of an oxidising agent, which comprises applying thereto at least one composition containing a cosmetically acceptable medium and a dyestuff corresponding to the formula: ##STR7## in which R denotes a linear or branched lower alkyl group which is optionally substituted by one or two hydroxyl groups, n is equal to 1, 2 or 3, m is equal to 0, 1 or 2 such that n+m is equal to 2 or 3, with the proviso that (i) if m is equal to 0 (and n is equal to 2 or 3), the OH groups occupy the following positions of the ring:

______________________________________2 3 4 5 6______________________________________ OH OHOH OH OH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OH______________________________________

and (ii) if m and n both denote 1, the substituents occupy the following positions of the rings:

______________________________________2 3 4 5 6______________________________________OH OROR OH OH OR OH OROH OROH OCH.sub.2 CH.sub.2 OH (3)OH ##STR8##OH OC.sub.2 H.sub.5______________________________________

or a bisulphite adduct thereof.

2. Process according to claim 1 in which the dyestuff corresponds to formula (I) as defined in claim 1 in which the substituents and the position thereof are as specified in the following table:

______________________________________Com-poundNo. 2 3 4 5 6______________________________________1 OH OH2 OH OH3 OH OH4 OH OH5 OH OH OH6 OH OH OH7 OH OH OH8 OH OH OH9 OH OH OH10 OH OCH.sub.311 OCH.sub.3 OH12 OH OCH.sub.313 OH OCH.sub.314 OH OC.sub.2 H.sub.515 OH OC.sub.2 H.sub.516 OH OH OCH.sub.317 OH OH OCH.sub.318 OH OH OCH.sub.319 OH OCH.sub.3 OH20 OH OH OCH.sub.321 OH OCH.sub.3 OH22 OH OCH.sub.3 OH23 OH OH OCH.sub.324 OH OCH.sub.3 OH25 OH OH OCH.sub.326 OH OH OCH.sub.327 OH OCH.sub.3 OH28 OCH.sub.3 OH OH29 OH OH OCH.sub.330 OCH.sub. 3 OH OH31 OH OCH.sub.3 OH32 OH OC.sub.2 H.sub.5 OH33 OH OH OC.sub.2 H.sub.534 OH OCH.sub.3 OCH.sub.335 OCH.sub.3 OH OCH.sub.336 OH OCH.sub.3 OCH.sub.337 OCH.sub.3 OH OCH.sub.338 OH OCH.sub.3 OCH.sub.339 OH OCH.sub.3 OCH.sub.340 OH OCH.sub.3 OCH.sub.341 OH OCH.sub.3 OCH.sub.342 OCH.sub.3 OH OCH.sub.343 OCH.sub.3 OH OCH.sub.344 OH OCH.sub.3 OCH.sub.345 OH OCH.sub.3 OCH.sub.346 OCH.sub.3 OCH.sub.3 OH47 OCH.sub.3 OH OCH.sub.348 OCH.sub.3 OH OCH.sub.349 OH OCH.sub.2 CH.sub.2 OH50 OH ##STR9##______________________________________

3. Process according to claim 1 in which n+m is equal to 3.

4. Process according to claim 1 in which m is 0 and n is 2, the two OH groups being in the 2,6- or 3,5-positions.

5. Process according to claim 1 in which the dyestuff is applied in an acid medium.

6. Process according to claim 5, in which the dyestuff of formula (I) is one in which the substituents and the position thereof are as specified in the following table:

______________________________________2 3 4 5 6______________________________________ OH OHOH OHOH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OH OCH.sub.3OH OH OCH.sub.3OH OH OCH.sub.3OH OCH.sub.3 OHOH OH OCH.sub.3OH OCH.sub.3 OHOH OCH.sub.3 OHOH OH OCH.sub.3OH OCH.sub.3 OH OH OH OCH.sub.3______________________________________

7. Process according to claim 1, in which the dyestuff is applied in an alkaline medium.

8. Process according to claim 7, in which the dyestuff of formula (I) is one in which the substituents and the position thereof are as specified in the following table:

______________________________________2 3 4 5 6______________________________________ OH OHOH OH OHOH OH OHOH OH OHOH OH OH OH OH OHOH OCH.sub.3 OCH.sub.3OCH.sub.3 OH OCH.sub.3 OH OCH.sub.3 OCH.sub.3 OCH.sub.3 OH OCH.sub.3______________________________________

9. Process according to claim 1, in which the dyestuff is applied in the form of a poultice with one or more powdered solids, and after the fibres have been impregnated, they are rinsed and dried.

10. A composition suitable for dyeing keratin fibres, which contains, in a diluent or carrier, at least one dyestuff corresponding to the formula defined in claims 1 or 2.

11. A composition according to claim 10, in which the dyestuff is one in which n+m is equal to 3.

12. A composition according to claim 11, in which the dyestuff is one in which m is 0 and n is 2, the two OH groups being in the 2,6- or 3,5-positions.

13. A composition according to claim 10, in which the dyestuff is 2,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde or 4-hydroxy-3,5-dimethoxybenzaldehyde.

14. A composition according to claim 10 which is in the form of a poultice powder comprising a clay, silica, flour, starchy or mucilaginous substance and a powdered plant.

15. A composition according to claim 10 which contains one or more direct dyestuffs and/or other natural dyestuffs.

16. A composition according to claim 10 in which the diluent is aqueous and contains one or more surface-active agents, organic solvents, thickeners, antioxidants, penetrating agents, sequestering agents, film-forming polymers, buffers, alkalising or acidifying agents or perfumes.

17. A composition according to claim 10 in which the dyestuff of formula I is present in an amount from 0.05 to 10% by weight.