A novel and chemoselective preparation of chlorosulphonyl-containing azo-dyes with phosphoryl chloride–N,N-dimethylacetamide

Azo dyes containing a chlorosulphonyl group (1b)–(10b) have been prepared by the reaction of the corresponding sodium sulphonates (1a)–(10a) with phosphoryl chloride–N,N-dimethylacetamide (in acetonitrile); the chemoselectivity of this reagent is superior to phosphoryl chloride, phosphoryl chloride–N,N-dimethylformamide, and thionyl chloride–N,N-dimethylformamide. By-products of the latter reactions have been isolated and characterized.