Acid-catalysed hydrolysis of cyanamides: estimates of carbodi-imide basicity and tautomeric equilibrium constant between carbodi-imide and cyanamide

Abstract

N-Cyanourea is demonstrated as an intermediate in the hydrolysis of dicyanamide which is shown to react as its carbodi-imide tautomer. The hydrolysis of N-cyanourea, dicyanamide, and NN′-dimethyl-cyanoguanidine is specific acid-catalysed. General acid catalysis is demonstrated for the hydrolysis of NN′-dimethylcyanoguanidine and is considered to be specific acid-nucleophilic. Assuming the carbodiimide mechanism also holds for the specific acid-catalysed hydrolysis of cyanamide the tautomeric equilibrium constant for formation of the parent carbodi-imide in water at 25° is estimated to be 0.6 × 10^–7 and the pK of the protonated carbodi-imide (H₂[graphic omitted]CNH ⇌ H⁺+ HNCNH) is estimated to have a value within one unit of zero. Rate constants are reported for alkaline hydrolysis of cyanamides.