1.2.4- Triazolidin-3,5-dione

Hydroxytriazoles and their tautomeric triazolinones have a common mesomeric anion and the spectra change in the presence of base. The predominately dioxo structure of 4-phenyl-1,2,4-triazolidine-3,5-dione is supported by the electronic spectrum. 

The cleavage of the 1,2,4-triazolidine-3,5-diones prepared with 3//-l,2,4-triazole-3,5(4//)-diones requires prolonged treatment with potassium hydroxide in refluxing water-ethylene glycol35 or reduction by lithium aluminum hydride in refluxing tetrahydrofuran36. The 1,2,4-triazolidine-3,5-dione derived from 4-(4-nitrophenyl)-3//-l,2,4-triazole-3,5(4/f)-diones should be more easily hydrolyzed 31. The hydrazinolysis of the 1,2,4-triazolidine-3,5-diones should also be a useful and mild procedure38. 

A soln. of 5-phenyl-3-(benzylidene-2-phenylcarbazoyl)-l,3,4-oxadiazol-2(3//)-one in 12 1 ethanol/water containing coned. HCl heated under reflux for 45 min - 4-benzamido-1-phenyl-1,2,4-triazolidine-3,5-dione. Y 72%. F.e.s. R. Milcent et al., J. Heterocyc. Chem. 26, 231-6 (1989). 

A, A -Dialkylamino isocyanates 153, generated from l,l-dimethyl-4-t-butyl-1,2,4-triazolidine-3,5-dione-l,2-aminimide 152, react with aliphatic isothiocyanates to give the [3+2] cycloadducts 154 resulting from addition across the C=N bond of the isothiocyanate... 

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