The Chemistry of Dyestuff. Intermediate Compounds. XI. Sulphur Compounds

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)Thio compounds are not used to a large extent in the production of dyestuffs, except perhaps in some of the vat dyes, many of these dyes themselves being thio compounds. The thio derivatives are, generally speaking, stable bodies and many of them give colours that are fairly fast to light, etc.

Many of the thio derivatives are extremely dangerous substances on account of their action upon the skin, causing eczema and blood poisoning. For this reason many of these compounds are converted into dyestuffs without purification.

Thioaniline [] (M.P. 105°C.) is employed in the production of a few azo dyes. It is obtained by heating aniline with sulphur at 150 to 160°C., until sulphuretted hydrogen is no longer given off. The excess of aniline is then removed by steam distillation and the thioaniline separated as sulphate by addition of sulphuric acid.

Dehydrothio-paratoluidine [] (M.P. 191°C., B.P. 434°C.) is obtained, together with Primuline base, by heating paratoluidine (seven parts) with sulphur (four parts) at 180° to 250°C. until sulphuretted hydrogen is no longer evolved. It is then separated from the primuline base by extraction with solvents.

It is a yellow crystalline body, sparingly soluble in water, fairly soluble in alcohol. Its salts are decomposed by water, and its diazo salts are easily soluble.

The sulphonic acid is prepared from the above base by heating at 40° to 50°C. with fuming sulphuric acid (50 per cent. SO₃ ). It crystallises in needles or leaflets, almost insoluble in water.

Dehydrothioxylidine [] (M.P. 107°C., B.P. 283°C. at 14 mm.) is prepared similarly to the above base, the temperature being maintained at 185° to 190°C., until sulphuretted hydrogen is no longer evolved. The product is distilled in vacuo and extracted with hydrochloric acid (30 per cent.) in which the base is soluble, whereas isodehydrothioxylidine, formed simultaneously, is insoluble in hydrochloric acid.

It forms yellowish-white prisms.

The isodehydrothioxylidine [] (M.P, 121 C,) forms yellow needles.