Kinetics and pressure dependence of the decomposition of the propionyl radical

Abstract

The kinetics and pressure dependence of the decomposition of the propionyl radical have been studied, by generation the radicals from the selective photolysis of azoethane in the presence of propionaldehyde, between 30 and 80°C. The following high- and low-pressure limiting rate constants for the radical decomposition have been obtained by a Hinshelwood-Lindemann treatment: log₁₀k_∞= 13.32–14,700/2.3RT(sec^–1) and log₁₀k₀= 15.64–10,500/2.3RT(mole^–1 cm³ sec^–1). The number of effective oscillators (Slater's theory) in the activated radical is 14 and the half-rate pressure (P_½) is 110 mm at 42°C. The heat of formation of the propionyl radical is calculated to be ΔH^°_f(C₂H₅CO)=–11.0±2 kcal mole^–1 and bond dissociation energies in propionaldehyde and methyl ethyl ketone are deduced.