Efficiency, monitoring and control of microwave heating within a continuous flow capillary reactor

We describe a method of monitoring temperature within a continuous flow capillary reactor (800 μm, outer diameter 1.2 mm and total length 138 mm) by measuring the change in electrical conductivity of a solution undergoing heating due to interaction with microwave energy. The method has been used to determine the extent of microwave heating as a function of liquid flow rate for solvents of differing microwave absorption properties. Deposition of gold metal on the outside surface of a glass capillary reactor was found to improve the efficiency of the microwave heating process. The alkylation of 2-pyridone with benzyl bromide, performed in DMF solution containing 0.01N NaBr, has been used to illustrate the suitability of the proposed methodology for monitoring the reaction temperature.