The oxidation of iso butane catalyzed by hydrogen bromide

Abstract

The oxidation of iso butane catalyzed by hydrogen bromide in a static system between 125 and 250°C has been investigated. In a boric-acid-coated vessel below about 170°C the overall process up to about 70% reaction was mainly (CH 3 ) 3 CH + O 2 = (CH 3 ) 3 COOH, the pressure decrease being a valid measure of the extent of reaction. The rate rose from a very small initial value to a maximum and then decreased. The plot of the rate at any time versus the square root of the pressure decrease was a straight line during the first 10 to 20% of the reaction. The variation of the slope of this line (a measure of the rate of oxidation ρ during the initial stages) and of the maximum rate with conditions showed that at 145°C ρ∝ [C 4 H 9 OOH] ½ [C 4 H 10 ] ½ [H Br] and ρ max . ∝ [C 4 H 10 ] [H Br]. Added inert gas or packing the vessel had little effect on the rate, but the reaction was accelerated by added bromine, t -butylhydroperoxide and di- t -butylperoxide. Many alcohols retarded the oxidation and traces of some even caused an induction period. Above about 170°C the pressure dropped to a minimum and then rose due to decomposition of the hydroperoxide formed. It is suggested that at 145°C autocatalysis was due to the reaction of a small proportion of the t -butylhydroperoxide produced with hydrogen bromide to give radicals, and that the main chain carriers are bromine atoms and t -butylperoxy radicals the former abstracting hydrogen from iso butane and the latter from hydrogen bromide in the propagation steps.