6-Substituted s-triazolo[4,3-b]-s-tetrazine-3-thiols: a sensitive and specific test for aldehydes

Abstract

4-Amino-5-hydrazino-1,2,4-triazole-3-thiol reacts in acid solution with benzaldehyde to give the 4-benzylideneamino-derivative, and in alkalin solution, under nitrogen, to give the 5-benzylidenehydrazino-isomer. The latter cyclises to give 5,6,7,8-tetrahydro-6-phenyl-s-triazolo(4,3-b)-s-tetrazine-3-thiol, which in the presence of aerial oxygen is coverted rapidly into the purple coloured 6-phenyl-s-triazolo-[4,3-b]-s-tetrazine-3-thiol, the chromogen of the triazolotetrazine test for aldehydes. In the absence of oxygen, the 5-benzylidenehydrazinotriazole slowly undergoes an irreversible isomerisation via the tetrahydrotriazolotetrazine to the 4-benzylideneamino-isomer.