Of particular interest was the hitherto unknown reaction between diethyl carbonate and 4- substituted thiosemicarbazides which might lead to the desired products in a direct reaction sequence. The reaction, however, took a quite different course. When refluxing 4- phenylthiosemicarbazide and diethyl carbonate in ethylene glycol monomethyl ether, 2, 5- dianilino-1, 3, 4-thiadiazole (111, R=
