The solubility of toluene and benzene in concentrated aqueous sulfuric acid; implications to the kinetics of aromatic sulfonation

The solubility of benzene and toluene in aqueous sulfuric acid > 75 wt-% has been determined at 5, 25 and 45°. Molar heats of solution have been calculated. The benzene to toluene activity coefficient ratio is slightly greater than unity. The relatively large difference in activation entropy for sulfonation of the para-position in toluene and a single position in benzene1 is therefore attributed mainly to differences in solvation of the transition states.