GB410192A - Process for the manufacture of azo-dyestuffs - Google Patents

Abstract

Azo dyes free from heavy metals but capable of forming complex metal compounds are made by treating azo dyes containing copper or chromium in complex form with an agent capable of splitting off the metal. The following methods are specified: (1) the metal is precipitated as a difficulty soluble compound, e.g. in the case of copper as the sulphide; (2) the metal compound is treated with a substance having a stronger affinity for the metal, e.g. organic polyhydroxy compounds, such as oxalic, tartaric and citric acids, or (3) with a strong acid, e.g. sulphuric, hydrochloric or formic acids. The method is useful for making o-oxyazo dyes which are only obtained with difficulty by the usual methods, e.g. the dyestuff 4 - chlor - 2 - aminophenol --> 2 - naphthol - 6 : 8 - disulphonic acid which cannot be obtained by the usual process may be made by coppering the dye 4-chlor-2-anisidine --> 2-naphthol-6 : 8-disulpho acid and then removing the copper. Similarly dyes derived from 3 : 3<1>-dioxy-4 : 4<1>-diaminodiphenyl may be made via the corresponding alkyl ethers or acyl compounds. The metal free compounds may be after-treated with metal compounds on the fibre. In examples: (1) the copper compound of the above-mentioned monoazo dye is treated with sodium sulphide to remove the copper; (2) the coppered dyestuff dianisidine \sQ b -naphthyl-3-methyl-5-pyrazolone-8<1>-sulpho acid is treated as in (1); the soluble o-oxyazo dyestuff dyes cotton, silk and viscose which yield bordo-red shades on after coppering; (3) the chromium compound of the dye 5-nitro-2-aminophenol --> 2-naphthylamine-6-sulphonic acid is treated with sulphuric acid; the o-oxyazo compound dyes wool in green shades after chroming; (4) the copper compound of the dyestuff benzidine-3 : 3<1>-dicarboxylic acid \sQ phenyl J acid is boiled with sodium sulphide. The Specification as open to inspection under Sect. 91 comprises also an example in which the copper compound of azosalicylic acid is treated with sodium sulphide or hydrochloric acid to remove the metal. This subject-matter does not appear in the Specification as accepted.