GB631262A - Manufacture of disazo-dyestuffs - Google Patents

Abstract

Diazo dyestuffs free from sulphonic acid groups are made by coupling tetrazotized 3 : 31-dihydroxy-benzidine with a hydroxynaphthalene, capable of coupling in a position vicinal to a hydroxyl group, in the presence of pyridine in an amount more than 25 per cent calculated on the weight of the coupling mixture. The dyestuffs are preferably symmetrical, but asymmetrical dyestuffs can be obtained by using 1 mol. each of two different hydroxy-naphthalenes with 1 mol. of tetrazotized dihydroxy-benzidine. Preferred hydroxynaphthalenes are b -naphthol, various dihydroxynaphthalenes and their mono, alkyl and hydroxy-alkyl ethers, amino-naphthols and hydroxy-naphthalene sulphonamides, particular compounds being specified. The tetrazotized dihydroxy-benzidine in the form of a filter cake is mixed with the coupling component and pyridine and the necessary alkali (e.g. alkali metal hydroxide or carbonate) run in as a concentrated aqueous solution, after which the coupling mixture is worked up in the usual way. The products are suitable for dyeing various materials, e.g. linen, cotton, artificial silk and staple fibres of regenerated cellulose. They may be converted in substance, in the dyebath or on the fibre into complex metal compounds, e.g. of copper, chromium, iron, nickel, cobalt or more than one of these, preferably by the process of Specification 455,274. The metal compounds can be used for colouring masses or solutions thereof, e.g. nitrocellulose lacquers, artificial resins or spinning masses. Examples show the preparation of typical dyestuffs and the application of one of them to the dyeing of cotton. Specification 609,300 also is referred to.