GB413344A - Improvements in the manufacture and production of sulphuric esters of leuco compounds of vat dyestuffs - Google Patents

Abstract

Leuco vat-dyes, sulphuric esters of.--Reduction products of vat-dyes which are stable in the air and substantially insoluble in dilute aqueous alkalis, are treated with agents supplying sulphur trioxide in presence of organic bases, preferably tertiary organic bases to give sulphuric esters of the leuco compounds. The starting materials are obtained by reducing vat-dyes in slightly alkaline or neutral, but preferably in acid media in presence of solvents or diluents, and then heating until compounds which are difficulty soluble or insoluble in cold aqueous solutions of alkalies are formed (cf. Specification 395,183). Thus in the case of dyes of the indigo and thioindigo series they may be converted to leuco compounds in known manner and then heated at 50--100 DEG C.; or reduction may be by hydrogen under pressure or by means of other reducing agents and the further heat treatment may be effected with simultaneous evaporation or distillation of solvent. In the case of anthraquinone vat-dyes, similar treatment may be employed or reduction may be effected by means hydroxy-methane sulphinic acid sodium salt at temperatures of 95--100 DEG C. until the stable products are deposited. Advantageously vat-dyes containing substituents such as halogen, alkyl, aryl, oxyalkyl may be so converted to starting-materials for the present process. In examples, the stable reduction products of the following vat-dyes are converted into leuco sulphuric esters by chlorsulphonic acid or its ethyl or methyl esters in presence of pyridine or dimethylaniline :-5,5<1>,7,7<1>-tetrachlorindigo (cf. example 1 of Specification 395,183), 4,4<1>-dichloro-5,5<1>-dibromindigo (cf. example 8 of Specification 395,183), 4,4<1> - dimethyl - 6,6<1> - dichlorthioindigo (prepared by heating the dye with alkaline hydrosulphite at 70 DEG C. and acidifying with bisulphite), 5,5,7,7<1>-tetrabromindigo (cf. example 6 of Specification 395,183), 2,6-diphenyl-1,3,5-triazine-4-carboxy-(a -amino -anthraquinone) (prepared by reducing the dye in pyridine with sodium hydrosulphite and heating at 55 DEG C.), N-dihydro-1,2,2<1>,1<1>-anthraquinoneazine (prepared by reducing the dye in triethanolamine with hydroxymethanesulphinic acid sodium salt, and heating to 95--100 DEG C.), and 3,3<1>-dichloro-N-dihydro-1,2,2<1>,1<1>-anthra quinoneazine (prepared as immediately preceding).