Alternative and one-pot synthesis of new conjugated 5-aryl-1,3,4-thiadiazole azo dyes

Abstract

New conjugated 2-phenylazo-1,3,4-thiadiazole derivatives were obtained using an alternative approach to the classical diazotization-coupling sequence. The elaborated methodology making use of N'-(2-phenylhydrazinecarbonyl)benzhydrazide precursors comprises their thionation by diphosphorus pentasulfide, subsequent cyclization to give the 1,3,4-thiadiazole moiety, and a final dehydrogenation using sodium nitrite. The innovative procedure allows to obtain azo compounds containing electron-donating and electron-withdrawing substituents, which is hardly to get in the classical approach. The X-ray single crystal structures of representative azo dyes are presented.