الملخص

ABSTRACT In this paper the synthesis of some substituted 1,3,4-oxadiazoles, 1,3,4-thiadiazoles and 1,2,4-triazoles is reported. Ethyl methacrylate was treated with hydrazine hydrate in ethanol to give the corresponding hydrazide (1). The hydrazide was converted to 1-acyl thiosemicarbazide (2) byits reaction with ammonium thiocyanate, which was treated with sodium hydroxide solution and with concentrated sulfuric acid to give 5-substituted-1,2,4-triazoles-3-thiol (3) and 2-substituted-5-amino-1,3,4-thiadiazole (4) respectively. The acid hydrazide (1) was treated with benzaldehyde or substituted benzaldehyde to give hydrazones (7-12), the hydrazones were then cyclized with lead dioxide to 2-subtituted-5-phenyl 1,3,4-oxadiazole (14). The reaction of the hydrazide (1) with formic acid gave 1-formyl-2-acyl hydrazine (6) and the cyclization of (6) by phosphorus pentaoxide gave monosubstituted-1,3,4-oxadiazoles (13). Acid hydrazide (1) was treated with phenyl isothiocyanate to give substituted thiosemicarbazide (5).