Oxidation base derived from 1-hexyl-4,5-diaminopyrazole, composition containing same and use thereof in oxidation dyeing of keratin fibres

Abstract

The present invention relates to novel 1-hexyl-1H-pyrazole-4,5-diamine derivative compounds of formula (I), to a composition for oxidation dyeing of the keratin fibres containing same, to a process for preparing the compounds of formula (I), to reaction intermediates, to an oxidation dyeing process using the composition, to the use of the compounds of formula (I) for oxidation dyeing of keratin fibres, and also to a kit; and to the 1-hexyl-4,5-diaminopyrazole derivative compounds of formula (I) below: ##STR00001##
and also the addition salts thereof with organic or mineral acids, the tautomers thereof, and the solvates thereof such as hydrates, in which ALK is as defined in the description.

Claims

1. A compound chosen from compounds of formula 5A below: ##STR00020## solvates thereof, or mixtures thereof.

2. A composition for oxidation dyeing of keratin fibers, wherein the composition comprises i) at least one compound chosen from compounds of formula: ##STR00021## solvates thereof, or mixtures thereof; and iii) at least one coupling agent.

3. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from para-phenylenediamines, bis-phenylalkylenediamines, para-aminophenols, ortho-aminophenols, or heterocyclic bases different from the compounds of formula 5A.

4. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from para-phenylenediamine, para-toluenediamine, 2-chloro-para-phenylenediamine, 2,3-dimethyl-para-phenylenediamine, 2,6-dimethyl-para-phenylenediamine, 2,6-diethyl-para-phenylenediamine, 2,5-dimethyl-para-phenylenediamine, N,N-dimethyl-para-phenylenediamine, N,N-diethyl-para-phenylenediamine, N,N-dipropyl-para-phenylenediamine, 4-amino-N,N-diethyl-3-methylaniline, N,N-bis(β-hydroxyethyl)-para-phenylenediamine, 4-N,N-bis(β-hydroxyethyl)amino-2-methylaniline, 4-N,N-bis(β-hydroxyethyl)amino-2-chloroaniline, 2-β-hydroxyethyl-para-phenylenediamine, 2-methoxymethyl-para-phenylenediamine, 2-fluoro-para-phenylenediamine, 2-isopropyl-para-phenylenediamine, N-(β-hydroxypropyl)-para-phenylenediamine, 2-hydroxymethyl-para-phenylenediamine, N,N-dimethyl-3-methyl-para-phenylenediamine, N-ethyl-N-(β-hydroxyethyl)-para-phenylenediamine, N-(β,γ-dihydroxypropyl)-para-phenylenediamine, N-(4′-aminophenyl)-para-phenylenediamine, N-phenyl-para-phenylenediamine, 2-β-hydroxyethyloxy-para-phenylenediamine, 2-β-acetylaminoethyloxy-para-phenylenediamine, N-(β-methoxyethyl)-para-phenylenediamine, 4-aminophenylpyrrolidine, 2-thienyl-para-phenylenediamine, 2-β-hydroxyethylamino-5-aminotoluene, 3-hydroxy-1-(4′-aminophenyl)pyrrolidine, addition salts thereof with an acid, or mixtures thereof.

5. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from N,N′-bis(β-hydroxyethyl)-N,N′-bis(4′-aminophenyl)-1,3-diaminopropanol, N,N′-bis(β-hydroxyethyl)-N,N′-bis(4′-aminophenyl)ethylenediamine, N,N′-bis(4-aminophenyl)tetramethylenediamine, N,N′-bis(β-hydroxyethyl)-N,N′-bis(4-aminophenyl)tetramethylenediamine, N,N′-bis(4-methylaminophenyl)tetramethylenediamine, N,N′-bis(ethyl)-N,N′-bis(4′-amino-3′-methylphenyl)ethylenediamine, 1,8-bis(2,5-diaminophenoxy)-3,6-dioxaoctane, addition salts thereof, or mixtures thereof.

6. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from para-aminophenol, 4-amino-3-methylphenol, 4-amino-3-fluorophenol, 4-amino-3-chlorophenol, 4-amino-3-hydroxymethylphenol, 4-amino-2-methylphenol, 4-amino-2-hydroxymethylphenol, 4-amino-2-methoxymethylphenol, 4-amino-2-aminomethylphenol, 4-amino-2-(β-hydroxyethyl-aminomethyl)phenol, 4-amino-2-fluorophenol, addition salts thereof with an acid, or mixtures thereof.

7. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from 2-aminophenol, 2-amino-5-methylphenol, 2-amino-6-methylphenol, 5-acetamido-2-aminophenol, addition salts thereof, or mixtures thereof.

8. The composition according to claim 2, wherein the composition further comprises ii) at least one additional oxidation base chosen from 2,5-diaminopyridine, 2-(4-methoxyphenyl)amino-3-aminopyridine, 3,4-diaminopyridine, 3-aminopyrazolo[1,5-a]pyridine, pyrazolo[1,5-a]pyrid-3-ylamine, 2-acetylaminopyrazolo[1,5-a]pyrid-3-ylamine, 2-morpholin-4-ylpyrazolo[1,5-a]pyrid-3-ylamine, 3-aminopyrazolo[1,5-a]pyridine-2-carboxylic acid, 2-methoxypyrazolo[1,5-a]pyrid-3-ylamine, (3-aminopyrazolo[1,5-a]pyrid-7-yl)methanol, 2-(3-aminopyrazolo[1,5-a]pyrid-5-yl)ethanol, 2-(3-aminopyrazolo[1,5-a]pyrid-7-yl)ethanol, (3-aminopyrazolo[1,5-a]pyrid-2-yl)methanol, 3,6-diaminopyrazolo[1,5-a]pyridine, 3,4-diaminopyrazolo[1,5-a]pyridine, pyrazolo[1,5-a]pyridine-3,7-diamine, 7-morpholin-4-ylpyrazolo[1,5-a]pyrid-3-ylamine, pyrazolo[1,5-a]pyridine-3,5-diamine, 5-morpholin-4-ylpyrazolo[1,5-a]pyrid-3-ylamine, 2-[(3-aminopyrazolo[1,5-a]pyrid-5-yl)(2-hydroxyethyl)-amino]ethanol, 2-[(3-aminopyrazolo[1,5-a]pyrid-7-yl)(2-hydroxyethyl)amino]ethanol, 3-aminopyrazolo[1,5-a]5yridine-5-ol, 3-aminopyrazolo[1,5-a]5yridine-4-ol, 3-aminopyrazolo[1,5-a]5yridine-6-ol, 3-aminopyrazolo[1,5-a]5yridine-7-ol, 2-β-hydroxyethoxy-3-amino-pyrazolo[1,5-a]pyridine; 2-(4-dimethylpiperazinium-1-yl)-3-amino-pyrazolo[1,5-a]pyridine, 2,4,5,6-tetraaminopyrimidine, 4-hydroxy-2,5,6-triaminopyrimidine, 2-hydroxy-4,5,6-triaminopyrimidine, 2,4-dihydroxy-5,6-diaminopyrimidine, 2,5,6-triaminopyrimidine, 4,5-diamino-1-methylpyrazole, 4,5-diamino-1-(β-hydroxyethyl)pyrazole, 3,4-diaminopyrazole, 4,5-diamino-1-(4′-chlorobenzyl)pyrazole, 4,5-diamino-1,3-dimethylpyrazole, 4,5-diamino-3-methyl-1-phenylpyrazole, 4,5-diamino-1-methyl-3-phenylpyrazole, 4-amino-1,3-dimethyl-5-hydrazinopyrazole, 1-benzyl-4,5-diamino-3-methylpyrazole, 4,5-diamino-3-tert-butyl-1-methylpyrazole, 4,5-diamino-1-tert-butyl-3-methylpyrazole, 4,5-diamino-1-(β-hydroxyethyl)-3-methylpyrazole, 4,5-diamino-1-ethyl-3-methylpyrazole, 4,5-diamino-1-ethyl-3-(4′-methoxyphenyl)pyrazole, 4,5-diamino-1-ethyl-3-hydroxymethylpyrazole, 4,5-diamino-3-hydroxymethyl-1-methylpyrazole, 4,5-diamino-3-hydroxymethyl-1-isopropylpyrazole, 4,5-diamino-3-methyl-1-isopropylpyrazole, 4-amino-5-(2′-aminoethyl)amino-1,3-dimethylpyrazole, 3,4,5-triaminopyrazole, 1-methyl-3,4,5-triaminopyrazole, 3,5-diamino-1-methyl-4-methylaminopyrazole, 3,5-diamino-4-(β-hydroxyethyl)amino-1-methylpyrazole, addition salts thereof, or mixtures thereof.

9. The composition according to claim 2, wherein the iii) at least one coupling agent is chosen from 1,3-dihydroxybenzene, 1,3-dihydroxy-2-methylbenzene, 4-chloro-1,3-dihydroxybenzene, 2,4-diamino-1-(β-hydroxyethyloxy)benzene, 2-amino-4-(β-hydroxyethylamino)-1-methoxybenzene, 1,3-diaminobenzene, 1,3-bis(2,4-diaminophenoxy)propane, 3-ureidoaniline, 3-ureido-1-dimethylaminobenzene, sesamol, 1-β-hydroxyethylamino-3,4-methylenedioxybenzene, α-naphthol, 2-methyl-1-naphthol, 6-hydroxyindole, 4-hydroxyindole, 4-hydroxy-N-methylindole, 2-amino-3-hydroxypyridine, 6-hydroxybenzomorpholine, 3,5-diamino-2,6-dimethoxypyridine, 1-N-(β-hydroxyethyl)amino-3,4-methylenedioxybenzene, 2,6-bis(β-hydroxyethylamino)toluene, 6-hydroxyindoline, 2,6-dihydroxy-4-methylpyridine, 1-H-3-methylpyrazol-5-one, 1-phenyl-3-methylpyrazol-5-one, 2,6-dimethylpyrazolo[1,5-b]-1,2,4-triazole, 2,6-dimethyl[3,2-c]-1,2,4-triazole and 6-methylpyrazolo[1,5-a]benzimidazole, 2-methyl-5-aminophenol, 5-N-(β-hydroxyethyl)amino-2-methylphenol, 3-aminophenol, 3-amino-2-chloro-6-methylphenol, addition salts thereof with an acid, or mixtures thereof.

10. The composition according to claim 2, wherein the iii) at least one coupling agent is chosen from compounds of formulae (II) and (II′): ##STR00022## organic or mineral acid or base salts thereof, solvates thereof, or mixtures thereof; wherein: X.sub.1 and X.sub.2, which may be identical or different, represent a group chosen from hydroxyl, (di)(C.sub.1-C.sub.6)(alkyl)amino, or (di)hydroxy(C.sub.1-C.sub.6)alkylamino; Y represents a hydrogen atom or (C.sub.1-C.sub.6)(hydroxy)alkyl, or two adjacent substituents Y and X.sub.1 and/or Y and X.sub.2 form, together with the carbon atoms which bear them, an optionally substituted heterocyclic group, or else two adjacent substituents Y and X.sub.1 form, together with the carbon atoms which bear them, a morpholinyl group optionally substituted with a (C.sub.1-C.sub.4)alkyl group; p is 1, 2, 3 or 4; t is 1, 2 or 3; it being understood that, when p or t is greater than or equal to 2, the Y groups are identical to or different from one another.

11. The composition according to claim 2, wherein the iii) at least one coupling agent is chosen from the compounds of formulae (II.sub.a) and (II′.sub.a): ##STR00023## organic or mineral acid or base salts thereof, solvates thereof, or mixtures thereof; wherein: X.sub.1 and/or X.sub.2 represent(s) a hydroxyl, amino, or (hydroxy)alkylamino group; Y.sub.1 represents a hydrogen atom or a (C.sub.1-C.sub.6)alkyl group; Y.sub.2 represents a hydrogen atom, or forms, with the substituent Y.sub.2, an optionally substituted heterocycle.

12. A method for dyeing keratin fibers, comprising applying the composition of claim 2 to the keratin fibers.

13. The method according to claim 12, wherein a color of the composition is revealed at acid, neutral, or alkaline pH by an oxidizing agent which is added to the dye composition at the time of use or which is present in an oxidizing composition applied to the keratin fibers simultaneously or sequentially with the application of the composition of claim 10.

14. The method according to claim 13, wherein the oxidizing agent is chosen from hydrogen peroxide, urea peroxide, alkali metal bromates, persalts, peracids, oxidase enzymes, or mixtures thereof.

15. A multi-compartment device, wherein the device comprises a first compartment comprising a dye composition as defined in claim 2 and a second compartment comprising an oxidizing composition.

16. The composition according to claim 2, wherein the total amount of compounds chosen from compounds of formula 5A and solvates thereof ranges from 0.001% to 10% by weight, relative to the total weight of the composition.

17. The composition according to claim 2, wherein the total amount of compounds chosen from compounds of formula 5A and solvates thereof ranges from 0.1% to 3% by weight, relative to the total weight of the composition.

18. The composition according to claim 2, wherein the total amount of coupling agents ranges from 0.001% to 10% by weight, relative to the total weight of the composition.

19. The composition according to claim 3, wherein the total amount of additional oxidation bases chosen from para-phenylenediamines, bis-phenylalkylenediamines, para-aminophenols, ortho-aminophenols, or heterocyclic bases different from compounds of formula 5A ranges from 0.001% to 10% by weight, relative to the total weight of the composition.

20. The composition according to claim 2, further comprising at least one additional component chosen from direct dyes; surfactants chosen from anionic, cationic, non-ionic, amphoteric, or zwitterionic surfactants; polymers chosen from anionic, cationic, non-ionic, amphoteric, or zwitterionic polymers; thickeners; antioxidants; penetrants; sequestrants; fragrances; buffers; dispersants; conditioning agents; film-forming agents; ceramides; preserving agents; opacifiers; or mixtures of two or more thereof.

Description

EXAMPLES

Synthesis Example

Process 1: Via a Nitro or Nitroso Reaction Intermediate

Preparation of 3-[2-hexylidenehydrazinyl]butanenitrile: Compound 2

(1) ##STR00014##

(2) 120 ml of 1-propanol and 42.6 g of hydrazine hydrate are charged, under nitrogen, to a three-necked reaction vessel equipped with magnetic stirring, a thermometer, a reflux condenser and a dropping funnel, and then, at 0° C., 60 g of crotonitrile 1 are run in dropwise. The stirring of the mixture obtained is maintained for 10 minutes at 0° C. and then for 1 hour at ambient temperature.

(3) 89.6 g of hexanal are then introduced dropwise and the stirring is continued for 20 minutes at ambient temperature before concentrating until a crude product 2 is obtained in the form of an orange oil (153.52 g). The product 2 thus obtained is used in the subsequent step without further purification.

(4) The spectroscopic and spectrometric analyses agree with the structure of the expected compound 2.

Preparation of 1-hexyl-3-methyl-1H-pyrazol-5-amine: Compound 3

(5) ##STR00015##

(6) Introduced, under nitrogen, into a 2-litre three-necked reaction vessel equipped with mechanical stirring, a thermometer, a reflux condenser and a dropping funnel are tert-butanol (1.6 l), the crude compound 2 (153.52 g), and potassium tert-butoxide (95 g). The suspension obtained is brought to 50° C. for a few minutes and then to reflux for 3 h 30. The reaction is monitored by TLC analysis (6/4 heptane/ethyl acetate). At the end of the reaction, the suspension was cooled to ambient temperature and then poured into 750 ml of water. The resulting mixture was extracted twice with diethyl ether. The combined organic phases were washed with a 1N hydrochloric acid solution. The aqueous phase was added to a saturated solution of NaCl salt and then a concentrated sodium hydroxide solution was added to basic pH before extraction twice with diethyl ether. The organic phase was dried over magnesium sulfate, filtered and concentrated so as to give an orange solid corresponding to the compound 3 (6.6 g). The organic phase previously obtained was partially concentrated to 2/3 and ethyl ether was added thereto. Concentrated sodium hydroxide was added to the resulting aqueous phase until a basic pH was obtained, followed by extraction twice with diethyl ether. The various organic phases were combined, dried over magnesium sulfate, filtered and concentrated so as to give a second batch of compound 3 in the form of an orange solid (129.6 g). The product was used in the subsequent step without further purification. The spectroscopic and spectrometric analyses agree with the structure of the expected compound 3.

Preparation of 1-hexyl-3-methyl-4-nitroso-1H-pyrazol-5-amine: Compound 4

(7) ##STR00016##

(8) In a 1-litre three-necked reaction vessel, equipped with mechanical stirring, a thermometer, a reflux condenser and a dropping funnel, a solution of crude compound 3 (50 g) in 270 ml of ethanol was prepared and then, after cooling to 0° C. and with stirring, 49 ml of isopentyl nitrile were added dropwise.

(9) The resulting solution was added dropwise to a solution of concentrated hydrochloric acid (27 ml) in dimethyl ether ethylene glycol (75 ml) precooled to 0° C. (exothermic reaction). The mixture obtained was kept stirring for 20 minutes and then concentrated to give a crude product (145.2 g).

(10) The crude obtained was resuspended in 600 ml of isopropyl ether with stirring overnight, before being filtered and dried so as to give a yellow solid (42.6 g). This solid was taken up in an MeOH/H.sub.2O mixture (70 ml, 6/4) and concentrated aqueous ammonia was added to the solution until a pH>11 was obtained, before being extracted 3 times with dichloromethane. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under vacuum so as to give a red/black solid (39.4 g). This solid was in turn taken up in dichloromethane, and the solution obtained was washed twice with water, dried over magnesium sulfate and filtered. The filtrate was treated with active carbon (5.5 g) and filtered on Celite so as to give the expected compound 4, isolated in the form of a red solid.

(11) The spectroscopic and spectrometric analyses agree with the structure of the expected compounds 4 (nitro et nitroso).

Preparation of 1-hexyl-3-methyl-1H-pyrazole-4,5-diamine: Compound 5

(12) ##STR00017##

(13) In a 2-litre three-necked reaction vessel, equipped with magnetic stirring, a thermometer, a reflux condenser and a dropping funnel, a suspension of the compound 4 (31.39 g) in ethanol (1.8 l) is prepared under an inert atmosphere, and palladium-on-charcoal (558 mg) and hydrazine (37.3 g) are added. The mixture is hydrogenated for 1 h at 70° C. and the end of the reaction is controlled by TLC (95/5 dichloromethane/methanol). The reaction medium is cooled to ambient temperature and filtered and the solid is washed with methanol. The filtrate is then concentrated so as to give the crude product which is then dissolved in ethyl acetate, and the solution obtained is washed twice with water.

(14) The organic phase was dried over magnesium sulfate, filtered and concentrated under vacuum so as to give a yellow solid (27.4 g) which was then taken up with pentane so as to give the expected compound 5 in the form of a yellow solid (25.5 g).

(15) The spectroscopic and spectrometric analyses agree with the structure of the expected compound 5.

Preparation of 1-hexyl-3-methyl-1H-pyrazole-4,5-diamine hemisulfate 5A

(16) ##STR00018##

(17) A solution of 7 g of sulfuric acid in 100 ml of a water/ethanol mixture is introduced into a round-bottomed flask equipped with magnetic stirring, and brought to 50° C.

(18) 25.5 g of 1-hexyl-3-methyl-1H-pyrazole-4,5-diamine 5 are then added and the mixture is maintained at 50° C. for 20 minutes. After concentration, the residue is triturated in 300 ml of acetonitrile so as to give a beige solid (30 g).

(19) This solid is finally taken up with 350 ml of a mixture of methanol and water (9/1). After filtration of the suspension at 0° C. and drying until the weight is constant, 15.7 g of 1-hexyl-3-methyl-1H-pyrazole-4,5-diamine hemisulfate (5A) are obtained in the form of a pink solid.

(20) The spectroscopic and spectrometric analyses agree with the structure of the expected compound 5A.

Process 3: (Via an Azo Intermediate)

(21) ##STR00019##
with R representing a hydrogen or halogen atom, a (C.sub.1-C.sub.4)alkyl group, or an SO.sub.3R′ group with R′ representing a hydrogen atom or an alkali or alkaline-earth metal, such as sodium.

(22) The benzenediazonium salts are easily accessible by conventional methods of organic synthesis or are commercially available. Mention may for example be made of benzenediazonium halides and in particular the following commercial benzenediazoniums: benzenediazonium chloride (BENZENEDIAZONIUM CHLORIDE-100-34-5), 2-methylbenzenediazonium chloride(2-METHYL-BENZENEDIAZONIUM CHLORIDE-2028-34-4), 3-methylbenzenediazonium chloride (3-METHYL-BENZENEDIAZONIUM CHLORIDE-2028-72-0), and para-diazobenzenesulfonic acid (P-DIAZOBENZENESULFONIC ACID, 305-80-6).

Examples of Dyeing

(23) The following dye compositions are prepared

(24) TABLE-US-00001 Amount Ingredients comp. a comp. b comp. c comp. d Compound 5A 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol Resorcinol 10.sup.−3 mol 3-aminophenol 10.sup.−3 mol 1H-indol-6-ol 10.sup.−3 mol 5-amino-2-methylphenol 10.sup.−3 mol Dyeing support (1) (*) (*) (*) (*) Demineralized water q.s. 100 g 100 g 100 g 100 g Shade observed beige light Brown- Purple- fuchsia beige beige Amount Ingredients comp. e comp. f comp. g comp. h Compound 5A 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol 3-6-hydroxybenzomorpholine 10.sup.−3 mol 2-methyl-5-hydroxyethyl- 10.sup.−3 mol aminophenol 2-amino-3-hydroxypyridine 10.sup.−3 mol 3-amino-2-chloro-6- 10.sup.−3 mol methylphenol Dyeing support (1) (*) (*) (*) (*) Demineralized water q.s. 100 g 100 g 100 g 100 g Shade observed Chromatic Vivid Fuchsia Vivid violet chromatic purple- purple violet Amount Ingredients comp. i comp. j comp. k comp. l Compound 5A 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol 10.sup.−3 mol 2-(2,4- 10.sup.−3 mol Diaminophenoxy)ethanol hydrochloride 2-methylresorcinol 10.sup.−3 mol 6-Methoxy-N2- 10.sup.−3 mol methylpyridine-2,3-diamine hydrochloride 1-naphthol 10.sup.−3 mol Dyeing support (1) (*) (*) (*) (*) Demineralized water q.s. 100 g 100 g 100 g 100 g Shade observed Dark Light Vivid Violet violet beige chromatic green (*): dyeing support (1) pH 9.5

(25) TABLE-US-00002 96° ethyl alcohol 20.8 g 35% aqueous sodium metabisulfite solution 0.23 g AM Pentasodium salt of diethylenetriaminepentaacetic 0.48 g AM acid as an aqueous 40% solution 60% aqueous solution of 3.6 g AM C.sub.8-C.sub.10 alkyl-polyglucoside Benzyl alcohol 2.0 g Polyethylene glycol containing 8 units of 3.0 g ethylene oxide NH.sub.4Cl 4.32 g Aqueous ammonia containing 20% NH.sub.3 2.94 g

(26) At the time of use, each composition is mixed with an equal weight of 20-volumes aqueous hydrogen peroxide solution (6% by weight). A final pH of 9.5 is obtained.

(27) Each mixture obtained is applied to locks of grey hair containing 90% white hairs. After a leave-on time of 30 minutes, the locks are rinsed, washed with a standard shampoo, rinsed again and then dried, so as to obtain the various shades.

(28) Comparative Tests

(29) hexyl-3-methyl-1H-pyrazole-4,5-diamine hemisulfate: compound 5A according to the invention hexyl-1H-pyrazole-4,5-diamine hemisulfate: Comparative

(30) The compound according to the invention and the comparative were tested in the same supports and under the same operating conditions as the previous examples.

(31) Resistance to Light (NV-RCL CAP 54)

(32) The locks dyed using the compositions described above were exposed to light according to the following protocol:

(33) The dyed locks are exposed to light using a Xenotest 150S machine from the company Atlas at an average lighting level (about 1250 W/m.sup.2 between 300 and 800 nm for 7 infrared filters).

(34) The humidity level is set at 60%. The exposure time is 40 hours.

(35) The colour of the locks was evaluated before and after exposure to light in the L*a*b* system, using a Minolta® CM 2002 spectrophotometer (Illuminant DE.sub.76). In this L*a*b* system, L* represents the intensity of the colour, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The lower the value of L, the darker or more intense the colour. The higher the value of a*, the redder the shade, and the higher the value of b*, the bluer the shade.

(36) The variation in the colour of the locks before and after exposure to light is measured by (ΔE) according to the following equation:
ΔE=√{square root over ((L*−L.sub.0*).sup.2+(a*−a.sub.0*).sup.2+(b*−b.sub.0*).sup.2)}

(37) In this equation, L*, a* and b* represent the values measured after exposure to light, and L.sub.0*, a.sub.0* and b.sub.0* represent the values measured before exposure.

(38) The greater the ΔE value, the greater the difference in colour of the lock before and after exposure, which shows a reduced light fastness.

(39) The results are reported in the table below

(40) TABLE-US-00003 Light Fastness Base coupler ΔE*.sub.76 1-hexyl-3-methyl-1H-pyrazole-4,5- 2-methylresorcinol 3.42 diamine hemisulfate 1-hexyl-1H-pyrazole-4,5-diamine 6.56 hemisulfate 1-hexyl-3-methyl-1H-pyrazole-4,5- 6-hydroxybenzomorpholine 2.13 diamine hemisulfate 1-hexyl-1H-pyrazole-4,5-diamine 4.86 hemisulfate 1-hexyl-3-methyl-1H-pyrazole-4,5- 2-amino-3-hydroxypyridine 4.7 diamine hemisulfate 1-hexyl-1H-pyrazole-4,5-diamine 7.48 hemisulfate 1-hexyl-3-methyl-1H-pyrazole-4,5- 2-({3-[(2-hydroxyethyl)amino]- 12.57 diamine hemisulfate 2-methylphenyl}amino)ethanol 1-hexyl-1H-pyrazole-4,5- 22 diamine hemisulfate
Chromaticity

(41) The chromaticity C* is defined according to the following equation:
C*=√{square root over (a*.sup.2+b*.sup.2)}

(42) In this equation, a* and b* represent the values measured on locks of hair after colouration. The higher the C*value, the better the chromaticity of the colour.

(43) TABLE-US-00004 Base coupler C* 1-hexyl-3-methyl-1H-pyrazole-4,5- 2-(2,4-diaminophenoxy)- 12.19 diamine hemisulfate ethanol hydrochloride 1-hexyl-1H-pyrazole-4,5-diamine 6.49 hemisulfate

(44) It appears that the dyes of the invention, i.e. 1-hexyl-4,5-diaminopyrazole substituted in position 3, make it possible to significantly improve the persistence to light and the chromaticity of the colours obtained on the keratin fibres after application compared with the comparative dyes not substituted in position 3.