Ohmic heating-assisted regioselective sulfonation of aniline: synthesis of sulfanilic acid

Abstract

The sulfonation of aniline with sulfuric acid was performed, for the first time, using the ohmic heating reactor technology. The effect of various operational conditions, such as the temperature, the stoichiometric amount (equimolar or excess) and concentration of sulfuric acid, the use of vacuum to remove water during heating, the geometry of the heating electrodes, the reaction time and heating method, on the reaction system was investigated. It was shown that ohmic heating is a viable technology to produce sulfanilic acid, which was obtained with 93% selectivity. Energetic advantages related to the heat transfer to the reaction system, such as high heating rate and low thermal inertia, were found when compared to the conventional heating method. These advantages highlighted the potential of ohmic heating as a technology to be applied in the development of more sustainable industrial processes, considering the increasing demand for clean processes and technologies to supply the current human needs without jeopardizing future generations.