Chemistry of biureas-II

Carbonohydrazide and its thio-analogue undergo di-addition with ethoxycarbonyl isothiocyanate. The reaction terminates at the mono-addition stage when one of the hydrazine moieties of the (thio)carbonohydrazide is blocked. The resulting 6-(substiiuted)amino-1-ethoxycarbonyl-thiobiureas and bithioureas are cyclised to the appropriate 1-ethoxycarbonamido-1,3,4-thiadiazoles by acids, and to mercapto-1,2,4-triazoles by alkalis.