New dyestuffs for synthetic fibres, benzimidazo‐thioxantheno‐isoquinolin‐ones

Abstract

Condensation of 3‐ and 4‐bromo‐ or nitro‐7H‐benzimidazo[2,1‐α]benz[d,e]isoquinolin‐7‐ones with 2‐aminobenzenethiol, followed by Pschorr cyclisation of the resultant product, afforded the isomer mixture of the new heterocycles benzimidazo[1,2‐b]thioxantheno[2,1,9‐d,e,f,]isoquinolin‐7‐one and benzimidazo[2,1‐a]thioxantheno[2,1,9‐d,e,f,]isoquinolin‐8‐one. Separation of these isomers and their characterisation by unambiguous synthesis is reported. Small amounts of analogous 5‐membered sulphur heterocycles were also formed by cyclisation in the β‐position of the naphthalene ring. These new heterocycles dye synthetic fibres in fluorescent orange and yellow shades, showing excellent fastness to light and sublimation. Principal mass spectra features of the compounds are given.