Planejamento sintético e caracterização de 2-(3- fenil -1,2,4 –oxadiazol -5-IL) fenol utilizando a irradiação de micro-ondas.

Abstract

The 1,2,4-oxadiazoles 3,5-disubstituted are an important class of heterocyclic substances due to their numerous technological, biological and pharmacological applications. These five membered heterocycles can be synthesized via the cycloaddition reaction or the Oacylation reaction followed by dehydration using different forms of energy. However, most of these methods involve high reaction times and the use of solvents or toxic reagents. In order to avoid these synthetic problems, the present study aimed to synthesize the 2-(3- phenyl-l,2,4-oxadiazol-5-yl) phenol from the ester ethyl salicylate, benzamidoxime in the presence of potassium carbonate using microwave irradiation. To reach this aim, the synthetic strategy was initially performing the synthesis of benzamidoxime and ester ethyl salicylate using as starting reagents the benzonitrile and salicylic acid, respectively. Once synthesized these compounds were performed the mapping of the higher incidence region of microwave irradiation, and the determination of the actual power of domestic microwave oven, aiming later synthesis of 2-(3-phenyl-l,2,4-oxadiazol-5-yl) phenol. Through the methodology adopted to benzamidoxime and ester ethyl salicylate were obtained with 61 and 53% yield after 17 and 12 h reaction time, respectively. The mapping of the region of greatest incidence of microwave irradiation has shown that the region around the central area of the dish of the domestic microwave oven absorbs a higher rate of electromagnetic radiation when the dish is rotating and when the plate is secured to higher radiation region is the right side of the furnace and the real power found was 626, 39 W. Finally, 2-(3-phenyl- 1,2,4-oxadiazol-5-yl) phenol was obtained with 47% yield after 2 min. of reaction. Based on the results the methodology led to the desired product in a short time reaction and in a good yield, besides demonstrating the feasibility of employment of a domestic microwave oven, when properly standardized.