Reaction between guaiacol and glyoxalic acid under microwave irradiation

Abstract

In this paper, we considered the opportunity to use microwave irradiation as an alternative to the convection heating method during the guaiacol condensation reaction with glyoxalic acid in an aqueous solution in the presence of sodium hydroxide in order to preparatively obtain the 4-hydroxy-3-methoxymindic acid, an intermediate of the vanillin synthesis. The experiments under the influence of the microwave irradiation were carried out using the «Speedwave four» microwave system that allowed varying the irradiation power in the range from 0 to 1450 W. The condensation reaction was carried out at the irradiation power of 290, 580, 870, and 1160 W. The effects of time, temperature and microwave radiation power on the desired product yield of the condensation reaction was established by varying the reaction conditions during the experiments. Using this method, the experimental conditions of highest product yield were determined when temperature of the reaction mixture, the irradiation power and synthesis time were 70 ºC, 870 W, and 30 minutes respectively. A comparison of the results of the synthesis of 4-hydroxy-3-methoxymindic acid under the microwave activation and for the conventional procedure was performed. The use of the microwave irradiation was found to significantly reduce (up to 20 times) the synthesis time, however, the maximum product yield achieved by this method turned out to be lower compared to the one obtained by conventional procedure. The 4-hydroxy-3-methoxymindic acid synthesized samples structure was confirmed using IR, 1H and 13C NMR spectroscopy.