Preparation of carbodiimides by the reaction of thioureas with diethyl azodicarboxylate

A new synthesis of disubstituted carbodiimides from N.N′-disubstituted thioureas, diethyl azodicarboxylate and triphenyl phosphine has been achieved. The intermediates of the reaction have been isolated and found to be 1:1 adducts of the thioureas and diethyl azodicarboxylate, N¹,N²-disubstituted—S—(N³,N⁴-biscarboethoxy)hydrazinoisothioureas which, on treatment with triphenyl phosphine at room temperature, afford the corresponding carbodiimides. Alternatively, the intermediates on heating under reflux in benzene or toluene, decompose to the carbodiimides, diethyl hydrazodicarboxylate and sulphur.