Linear Free Energy Relationships in Heterogeneous Catalysis. XIII. The Dehydration of Aliphatic Alcohols over Silica–Alumina

Abstract

Abstract In order to survey the applicability of linear free-energy relationships to the catalytic dehydration of aliphatic alcohols, isopropyl alcohol and n-, s-, and t-butyl alcohols were dehydrated over silica–alumina at 54–166 °C. The dehydration was zero order in alcohol over the pressure range of 0.01 to 0.1 atm. The true activation energies were 32.0, 35.3, 31.7, and 29.9 kcal/mol for isopropyl alcohol and n-, s, and t-butyl alcohols, respectively. The zero-order rate constants were exclusively affected by the activation energy. A linear relationship was found between the true activation energy, as well as the logarithm of the zero-order rate constant, and the heterolytic bond dissociation energy for the C–O bond in alcohols, D(R+OH−). The activation energy increased and the rate constant decreased with an increase in the D(R+OH−). These correlations were explained in terms of the heterolytic fission of the C–O bond in the rate-determining step.