The electrodeless discharge lamp: a prospective tool for photochemistry

Abstract

A simple photochemical reactor has been developed and tested for photochemical reactions. It consisted of an electrodeless discharge lamp (MWL) placed into the reactor vessel of a commercial microwave oven. The microwave (MW) field generated ultraviolet irradiation by the lamp at the same time as it interacted with a studied sample. This technique brings a unique possibility to study the simultaneous effect of both UV/VIS and MW irradiations on photochemical reactions. The use of MWL in a MW reactor has been studied in terms of (1) an operating MW power and temperature influence on the lamp, (2) solvent polarity influence, (3) MWL heating capabilities, and (4) dependence of the photoreaction efficiency on the MW power output. It was found that the lamp produced enough heat to quickly warm up any liquid to boil even in case of ‘transparent’ liquids in the MW field. An efficiency of light-induced photofragmentation reaction of valerophenone (Type II reaction) was investigated as a function of the MW input power and solvent polarity. It was found that conversions of acetophenone production showed almost linear dependence on the input MW power. Efficiencies in acetonitrile were higher than those obtained in benzene, only by a factor of 1.2, which was explained by lowering the MWL intensity, thanks to MW absorption by the solvent.