Synthesis and cyclisation of 1,4-disubstituted semicarbazides.

Semicarbazides, besides possessing medicinal properties, also find wide applications in agriculture and industry. We report in this article the synthesis of the four 1,4-disubstituted semicarbazides: 1-cinnamoyl-4-phenyl semicarbazide (1), 1-oleyl-4-phenyl semicarbazides (2), 1,1',1''-tricitryl-4,4',4''-triphenyl semicarbazide (3) and 1-benzoyl-4-phenyl semicarbazide (4), by the condensation of four different hydrazides: cinnamic acid hydrazide (5), oleic acid hydrazide (6), citric acid hydrazide (7) and benzoic acid hydrazide (8). The acid hydrazides were prepared by the condensation of four different acids with phenyl isocyanate. The semicarbazides were also subjected to acid catalysed intramolecular cyclisation. The cyclisation of (1) and (2) afforded substituted 1,3,4-oxadizoles: 2-cinnamoyl-5-aminophenyl 1,3,4-oxadizoles (9) and 2-oleyl-5-aminophenl 1,3,4-oxadizoles (10), respectively, in high yield, while no cyclisation occurred in the cases of (3) and (4). The products in each case have been identified on the basis of melting points and IR spectral studies.