Highly Selective Isobutane Hydroxylation by Ozone in a Pressure-Tuned Biphasic Gas–Liquid Process

Abstract

We have demonstrated a simple process for isobutane ozonation to tert-butyl alcohol (TBA) with 85%–90% selectivity in a biphasic gas–liquid process at ambient temperatures (16–18.5 °C) and mild pressures (∼0.6 MPa). The observed TBA selectivity is much higher than the value reported for either gas-phase ozonation or conventional noncatalytic air oxidation in liquid isobutane. The O3 utilization to form TBA is maximized (∼1.5 mol TBA/mol O3 consumed) by (a) adding optimum amounts of protic compounds (water and alcohols) in the reaction mixture, and (b) maintaining an optimum O3 partial pressure in the gas phase that limits the liquid-phase O3 concentration and minimizes O3 decomposition. The relatively low CO2 formation (<6% selectivity at optimal conditions) suggests that TBA formation occurs with high economy, predominantly via hydrotrioxide formation.