Synthesis of N-(3(5)-Aryl-1,2,4-triazol-5(3)-yl)-N'-carbethoxythioureas and Their Tautomerism in DMSO Solution

N-(3(5)-Aryl-1,2,4-triazol-5(3)-yl)-N'-carbethoxythioureas were prepared from ethoxycarbonyl isothiocyanate and 3(5)-amino-5(3)-aryl-1,2,4-triazoles. The annular prototropic tautomerism in the compounds was investigated by 1H NMR in DMSO solution. The tautomeric preferences depended on electronic properties of substituents on the phenyl ring and were well correlated with their Hammett constant values.