Azo direct dyes and method for dyeing hair using these dyes

A compound of formula (I) or (II) or (III):

• cosmetically acceptable salts thereof or mixtures thereof;
• wherein in formula (I), R5 and R6 are selected, independently from each other, from the group consisting of a C1-C6 alkylamino group, a C1-C6 alkylcyano group, a C1-C6 alkyl group, a C1-C6 alkoxy group, a benzyl group, a hydrogen atom, a C1-C6 hydroxyalkyl group, and a C4-C6 polyhydroxyalkyl group, wherein the alkyl groups are linear or branched;
• and
• wherein in formula (I) or (II) or (III), R7 is selected from the group consisting of a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a hydroxyl group, a nitro group, a cyano group, an acyl group, an aminoacyl group, and a methoxy group;
• wherein in formula (I) or (I) or (III), R8′, R8″ and R8″′ are selected, independently from each other, from the group consisting of a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a hydroxyl group, a hydroxylamine group, a nitroso group, a nitro group, a methoxymethyl group, an acyl group, an aminoacyl group, a methoxy group and a hydroxyalkyl group.