Reactions of the isopropoxyl radical. Part II. Pressure dependence and kinetics of pyrolysis at 160–200° in the gas phase

Abstract

The pressure dependence of the pyrolysis of the isopropoxyl radical has been demonstrated in the gas phase at 160–200°/20–230 mm., using isopropyl nitrite–nitric oxide mixtures. The reaction is in the transition region between first- and second-order. High- and low-pressure limiting values of the rate constant have been determined, with E_∞= 17·3 and E₀= 8·3 kcal. mol^–1, corresponding to twenty effective oscillators in the activated state, and A_∞= 10^11·8 sec.^–1 and A₀= 10^13·1 mol^–1 cm.³ sec.^–1. The efficiency in energy transfer of a wide range of added, chemically inert gases has been examined; molecules structurally similar to the isopropoxyl radical appear to have the highest efficiency.