From Thiosemicarbazides and Thio phosgene

From thiosemicarbazides and thio)phosgene. Sasse has carefully reexamined the old-established synthesis of 1,3,4-thiadiazolines from substituted thiosemicarbazides and (thio)phosgene. 

The interaction of 1,4,4-trisubstituted thiosemicarbazides (92) and phosgene proceeds uniformly, yielding l,3,4-thiadiazolin-5-ones (93). The use of 1,4-disubstituted thiosemicarbazides requires careful control of the conditions, since an excess of phosgene produces carbamoyl chlorides (95) or symmetrical ureas (96) instead of the desired 2-alkylamino-l,3,4-thiadiazolin-5-ones (94). However, both (95) and (96) are readily converted into (94) by alkali. The interaction of thiophosgene and 1,4-di- or 1,4,4-trisubstituted thiosemicarbazides proceeds analogously for details the extensive original paper should be consulted. 

The heterocyclic products show, in general, the expected properties the carbamoyl chlorides (95) are convertible into ureas (97 X = NHj etc,) or urethanes (97 X = OR), whereas the 2-alkylamino-l, 3,4-thiadiazolin-5-ones (94) are acylated to (98). They also yield, with thiophosgene, a series of thio-analogues of (95), (96), and (97).  

Sherman in Heterocyclic Compounds , ed. R. C. Elderfield, Wiley, New York, 

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