A new series of 1,3,4-oxadiazole derivatives were prepared from the condensation of acid hydrazide,5-bromo-2-(trifluoromethoxy)benzoic acid in POCl3 by ultrasonic irradiation method. The new synthetic method furnished the desired products in shorter time and good yields. The chemical structures of compounds 4a-h were confirmed by Fourier transform infrared spectroscopy (IR), proton nuclear magnetic resonance (1H-NMR), carbon nuclear magnetic resonance (13C-NMR) and elemental analyses. Larvicidal bioassay tests were performed using several 2-(5-bromo-2-(trifluoromethoxy) phenyl)-5-aryl-1,3,4-oxadiazole. These synthesized compounds presented strong larvicidal activity against urban mosquitoes Culex quinquefasciatus. The results suggest that larvicidal activity might be correlated with the presence of electron-withdrawing substituents in the para position of the phenyl ring. The alterations observed in the larvae spiracular valves of the siphon and anal papillae by 1,3,4-oxadiazoles in the larvicidal bioassay are responsible for larvae’s death.
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