The gas-phase reaction of acetic acid with hydrogen bromide. The effect of isobutene

Abstract

Addition of isobutene to reaction mixtures of acetic acid and hydrogen bromide brings about a lowering in the initial rate of pressure change. The lowering is proportional to the pressure of isobutene and is explained in terms of a molecular reaction producing mesityl oxide. Mesityl oxide is formed steadily throughout the course of the reaction in quantities proportional to the pressure of isobutene. The quantities of mesityl oxide detected are less than those required to account quantitatively for the lowering of dp/dt, but the presence of the products of the thermal reactions of mesityl oxide, and the minima observed in the pressure-time curves at 407� show that the discrepancies can be accounted for in terms of the polymerization undergone by mesityl oxide in the presence of hydrogen bromide. The reaction appears analogous to the formation of mesityl oxide by the acetylation of isobutene in solution.