Abstract: Under the combined assistance of microwave and ultrasonic, the synthesis of 2-methylbenzoxazole for use as a food flavor via the polyphosphoric acid-catalyzed reaction between 2-aminophenol and acetic acid was studied. Experimental investigations into the effects of catalyst type, 2-aminophenol-to-acetic acid molar ratio, 2-aminophenol-to-polyphosphoric acid (PPA) mass ratio, microwave power, ultrasonic power, microwave treatment alone, reaction temperature and reaction time on reaction yield of 2-methylbenzoxazole were carried out. The results showed that the optimal synthesis conditions of 2-methylbenzoxazole were microwave power of 800 W, ultrasonic power of 800 W, 2-aminophenol-to-PPA ratio of 3:4, acetic acid-to-2-aminophenol ratio of 7.6:1, reaction time of 25 min, and reaction temperature of 115 ℃. This optimized reaction and subsequent vacuum distillation resulted in a 2-methylbenzoxazole yield of 78.20%. The structure of the synthesized 2-methylbenzoxazole was confirmed by IR, MS and 1H NMR. The established process for 2-methylbenzoxazole synthesis from the inexpensive and easily available materials had the advantages of short reaction time, high yield and easy operation resulting from the synergistic action of microwave and ultrasonic and allowed the formation of purely aromatic products.

Key words: 2-methylbenzoxazole, 2-aminophenol, microwave, ultrasonic, flavor, synthesis