Anionic azo dyes and the metal complexes thereof ofr colouring leather

A process for dyeing leather, comprising treating leather with an aqueous solution of a dye wherein the dye comprises at least one anionic azo dye or a transition metal complex thereof, the anionic azo dye having at least one acidic group in the form of its salt and at least 2 azo groups and wherein dye anion is described by the general formula I

• where
• Q, R, T, U and V are independently a benzene, naphthalene, diphenylamine, diphenylmethane, phenylaminosulfonylbenzene or phenylaminocarbonyl-benzene radical and where Q and U may also be a pyrazole, thiazole, triazole, isothiazole or thiadiazole radical and as well as by the optionally present anionic group A− may optionally be substituted by one or more of the following radicals:
• OH, NH2, NO2, halogen, C1-C4-alkyl, C1-C4-hydroxyalkyl, C1-C4-alkoxy, C1-C4-alkylamino, C1-C4-dialkylamino, C1-C4-alkylaminocarbonyl,
• C1-C4-dialkylaminocarbonyl, C1-C4-alkylcarbonylamino,
• N-(C1-C4-alkylcarbonyl)-N-(C1-C4-alkylcarbonyl)amino, phenylcarbonylamino, formamide or N-attached 5- or 6-membered heterocyclyl, where Q and U may independently have an —N═N-P substituent, where P is an aromatic radical which is selected from the group consisting of phenyl, naphthyl, pyridyl, 2-pyridonyl, pyrazolyl and thiazolyl and wherein P is optionally substituted by one or more radicals selected from the group consisting of OH, NH2, NO2, halogen, C1-C4-alkyl, C1-C4-hydroxyalkyl, C1-C4-alkoxy, C1-C4-alkylamino, C1-C4-dialkylamino, C1-C4-alkylaminocarbonyl, C1-C4-dialkylaminocarbonyl, C1-C4-alkylcarbonylamino, N-(C1-C4-alkylcarbonyl)-N-(C1-C4-alkylcarbonyl)amino, phenylcarbonylamino, formamide, N-attached 5- or 6-membered saturated nitrogen heterocyclyl, morpholinyl, piperazinyl and pyrrolidinyl;
• S is a radical of the formulae A or B;
• where X and Y in the formula A are independently OH, NH2, C1-C4-alkyl, C1-C4-hydroxyalkyl, C1-C4-alkoxy, C1-C4-alkylamino, C1-C4-dialkylamino or N-attached 5- or 6-membered saturated heterocyclyl, W in the formula B is a bond, O, NH, SO2, SO2NH, CONH or C1-C4-alkylene, R1 and R2 are independently hydrogen, OH, or C1-C4-alkyl and each Z is the same or different and represents COOH or hydrogen;
• A− may at each instance be the same or different and is selected from the group consisting of CO2− and SO3−;
• k, l, m, n and o may be the same or different and are each 0, 1 or 2, provided the sum total pk+l+m+qn+ro is at least 1;
• p, q and r are independently 0 or 1;
• which comprise lithium ions and sodium ions in a molar ratio in the range from 1:19 to 4:1 and especially in a molar ratio in the range from 1:9 to 3.5:1.