Catalysis by hydrogen halides in the gas phase. XX. Propionic acid and hydrogen bromide

Abstract

Hydrogen bromide catalyses the decomposition of propionic acid at 405-468º. The initial products are ethyl bromide, carbon monoxide, and water; however, ethyl bromide decomposes into ethylene and hydrogen bromide at rates comparable with those of the initial reaction. The kinetic form of an individual run is therefore not simple, and initial pressure change has been used to measure the rate. The reaction,is first order in each reactant, and the variation of rate with temperature is given by K₂ = 1.36 x 10¹²exp(-30850/RT) s^-1 ml mol^-1 Comparison with the hydrogen bromide catalysed decarbonylations of other acids and esters has been made. Isobutene added to the reaction affects the kinetic form of individual runs slightly and mainly through its effect on the decomposition of ethyl bromide.