Reaction of hydrogen bromide with fluoroethylenes in the gas phase. Part 1.—The photoaddition of hydrogen bromide to tetrafluoroethylene

Abstract

The photoaddition of hydrogen bromide to tetrafluoroethylene has been studied in the gas phase using a wide variety of conditions. The rate expression is k₅[HBr]^z.frac32;(I₀/k₈)^½, where k₅ is the rate constant of the hydrogen-abstraction step, and k₈ is the rate constant of the dimerization of 1,1,2,2-tetrafluoro-2-bromoethyl radicals. The importance of dimerization as the chain terminator and the reported exothermicities of fluorocarbon reactions are interpreted in terms of an irreversible bromine atom+tetrafluoroethylene addition. The lack of any inert gas effect suggests that the intermediate addend radicals exist in their vibrational ground states. The activation energy, determined over a temperature range 50–130°C, is +2.28 ± 0.15 kcal/mole.