Reaction of thiourea S,S-dioxides with dyes containing carbonyl or azo groups

The kinetics of decomposition of thiourea and N-methylthiourea S,S-dioxides in alkaline aqueous medium and their reactions with oxygen, Indigo Carmine, and Acid Yellow 11 were studied. The decomposition of thiourea S,S-dioxides in weakly alkaline media was found to follow two pathways leading to the formation of ammonia and sulfoxylate ion, respectively. The second pathway predominates in strongly alkaline media. Thiourea S,S-dioxides can be used for selective reduction of azo compounds to the corresponding hydrazo derivatives.