The Effect of Pressure on the Rate of the Acid-catalyzed Hydration of Propylene

Abstract

Abstract In order to confirm whether a water molecule (or molecules) is held in a protonated activated complex by electrostatic interaction or by a partial valence bond, the pressure dependency of the activation volume, ΔV\ewq, for the hydration of propylene was measured at 180°C. The pressure effect on the rate of the hydration of propylene was studied in such dilute sulfuric acid solutions of a 0.0000108 mole fraction (0.00060n under S.T.P.) that the dielectric constant, D, and the density of pure water could be replaced for those of the reacting solution. The absolute value of the ΔV\ewq decreases steeply from 19 ml/mol at 300 kg/cm2 to 4 ml/mol at 5000 kg/cm2. The activation energies and entropies, obtained from the temperature dependency of the reaction rate, are 22.7 kcal/mol and −16.6 e.u./mol respectively at 1000 kg/cm2 and 21.9 kcal/mol and −17.0 e.u./mol respectively at 3000 kg/cm2. The ΔV\ewq is approximately proportional to the −∂D⁄D2∂p value, (D: dielectric constant of medium; p: pressure), which follows from the Krichevski equation; hence, it was concluded that the contraction of water around an activated complex by electrostatic interaction contributes to the ΔV\ewq and that a water molecule (or molecules) is held in the activated complex by electrostatic interaction. The case of a water molecule being held by a partial valence bond was discussed in terms of the molar volumes of the reactants.