Reactions of 2,4-disubstituted thiosemicarbazides with acetone catalyz
ed by sulfuric acid gave cyclic 1,2,4-triazolidine-3-thione derivative
s. The same reaction with no catalyzer gave open-chain compounds. Synt
hesis and X-ray studies of some 1,2,4-triazolidine-3-thiones are descr
ibed.