Production of p-toluenesulfonic acid by sulfonating toluene with gaseous sulfur trioxide

Toluene was sulfonated by gaseous sulfur trioxide to prepare p-toluenesulfo nic acid. The effects of reaction temperature and toluene conversion on the isomer selectivities and the dynamic viscosity of the reaction mixture in a well-stirred tubular glass reactor of 4cm diameter and 16 cm height were investigated. Lower selectivity to the m-isomer was obtained at lower react ion temperature and lower conversion of toluene, whereas the selectivity to the p-isomer seemed to be less affected by these parameters. With the incr ease in toluene conversion a sharp increase in viscosity of the reaction mi xture was observed, which was attributed to the saturation of the toluenesu lfonic acids dissolved in toluene. A pilot-scale stainless steel jet loop r eactor (JLR) of 0.3 m diameter and 4m height with an external cooler was co nstructed and used for the continuous sulfonation of toluene. It was found that the JLR was very effective for the fast removal of the large amount of reaction heat, and selectivities to the p-isomer around 85% and to the m-i somer below 1.2% were obtained. (C) 2001 Society of Chemical Industry.