Article

Abstract

Several different reactions have been studied to determine whether they occur more rapidly than conventionally heated reactions at atmospheric pressure. Small rate enhancements have been observed for some reactions carried out under microwave reflux in a modified domestic microwave oven. The Knoevenagel reaction of acetophenone with ethyl cyanoacetate was shown to have a rate enhancement of 2.5 times. However this reaction showed no rate increase over conventional heating, at the same temperature, in a variable-frequency microwave oven. It is therefore probable that the small rate enhancements observed in these experiments, using microwave heating, were due to hot spots or superheating of the solvent rather than to nonthermal effects.Key words: microwave, nonthermal effects, superheating, hot spots.