Effect of solvent on the hydration of 2-methyl-propene in solutions of p-toluenesulfonic acid and poly(styrenesulfonic acid)

Abstract

Results are reported of a kinetic study on the hydration of 2-methylpropene at 25.0 °C in solutions of p-toluenesulfonic acid and poly-(styrenesulfonic acid) in mixtures of 1,4-dioxane or sulfolane and water. Both cosolvents have a large influence on the rate of hydration. For sulfolane the rates are higher than for 1,4-dioxane, in spite of the higher solubility of the alkene in 1,4-dioxane/water mixtures. For the reactions catalyzed by p-toluenesulfonic acid, the variation of the pseudo first-order rate constant as a function of the solvent composition is explained in terms of the Hammett acidity function and an examination of the influence of the solvent on the initial- and transition-states of the reaction. Contrary to the rates of the reactions catalyzed by p-toluenesulfonic acid, the rates per equivalent of acid groups are independent of the acid concentration for the reactions catalyzed by poly(styrenesulfonic acid). This is explained by assuming that solutions of poly(styrenesulfonic acid) are divided into an ordered polymer-rich pseudo-phase and a highly disordered pseudo-phase in which the polymer concentration is very low. It appears that for the same overall mol fraction of the cosolvent, the amount of cosolvent in the ordered pseudo-phase is considerably higher for the rather polar sulfolane than for the almost non-polar 1,4-dioxane. The results of this study will give insight into the influence of the solvent composition on the catalytic activity of sulfonated polystyrene/ divinylbenzene-type cation exchange resins, which are used as catalysts for the hydration of lower alkenes on an industrial scale.