Conversion of thiobiurets to thiadiazolones and triazinones by oxidative cyclization

1-Aroyl-5-aryl-2-thiobiurets [2a-i] react with hydrogen peroxide in an acidic medium yielding the new 5-aroylamino-2-aryl-2H-1,2,4- thiadiazol-3-ones [3a-i]. On treatment with alkali, thiobiurets [2a- c] gave 6-aryl-4-thioxo-1,2,3,4-tetrahydro-1,3,5-triazin-2-ones [4a- c]. Structures of the new products were established by analytical and spectroscopic [IR, 1H-NMR and MS] results. A mechanism is proposed to explain the formation of compound [7]