Abstract
In order to study the hydrotropic action of organic sulfonic acids, solubilities were examined for benzene, toluene, naphthalene and biphenyl in water and in aqueous solutions of methane-, p-toluene and β-naphthalenesulfonic acid. Both p-toluenesulfonic acid and β-naphthalenesulfonic acid showed marked hydrotropic actions, but methanesulfonic acid did not show any appraisable action. From the solubility data the thermodynamic parameters for the transfer of one mole of the solute from water to the sulfonic acid solutions were calculated. It was found that the transfer process of every solute from water to the p-toluenesulfonic acid solution is endothermic and accompanies a large positive entropy change. On the contrary, the process of naphthalene and biphenyl from water to the β-naphthalenesulfonic acid solution is exothermic and accompanies little entropy change. From these results it is concluded that the action of organic sulfonic acids on the solubilities of aromatic hydrocarbons changes with the sizes of the solute and of the hydrophobic groups in the sulfonic acids.
