Tetrazole derivatives
A series of 1-(5-tetrazolyl)-3-phenyl-5-arylformazans, which are readily oxidized to brightly colored 2-(5-tetrazolyl)-3-aryl-5-phenyltetrazolium betaines in alkaline media, are obtained by coupling of arenediazonium salts containing strong electron-donor groups with 5-tetrazolylhydrazones. The formazans form deeply colored complexes with Ni2+, Cu2+, and Co2+ salts.