Reductive Removal of Mercapto-groups

Reductive Removal of Mercapto-groups. 2-Mercapto-l,3,4-thiadiazole, and the parent thiadiazole, which were hitherto only accessible by multi-stage syntheses, may readily be prepared from 2,5-dimercapto-l,3,4-thiadiazole by the successive removal of its mercapto-groups, by reductive cleavage of carbon-sulphur bonds with sodium in liquid ammonia. The 2-amino-5-mercapto-compound is similarly convertible into 2-amino-l,3,4-thiadiazole (up to 65%).  

Dimerization. The lithio-l,3,4-thiadiazole (120), formed by lithiation at —78 C, is methylated at low temperatures to give the 2-ethyl derivative, but it dimerizes at ambient temperatures to give (121). The open-chain thioimine (119) is isolable 

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