Pressure Effect and Mechanism in the Acid-Catalyzed Hydration of Propylene and Isobutylene

The effect of pressure up to 3 kbar on the rate of the acid-catalyzed hydration of propylene and isobutylene has been measured. The volumes of activation are: for propylene at 100 °C−9.6 ± ~1.0 cm3 mole−1, and for isobutylene at 35 °C− 11.5 ± ~1.0 cm3 mole−1. The effect of temperature in the range 90–120 °C on the rate of hydration of propylene at 100 bar was measured. At 100 °C the Arrhenius energy is 27.1 ± ~1.0 kcal mole−1 and the entropy of activation is −5.4 ± ~2.5 cal deg−1 mole−1. Both the volumes and entropies of activation strongly indicate that a molecule of water is present in the transition states, which can therefore be represented as [olefin. H+•H2O]≠. There appears to be no strong evidence regarding the molecular structure of the transition states.