Kinetics of the Reactions of Unsaturated Hydrocarbon Free Radicals (Vinyl, Propargyl, and Allyl) with Molecular Bromine

Article abstract of DOI:10.1021/j100133a016

The kinetics of the reactions of three unsaturated free radicals (vinyl, propargyl, and allyl) with molecular bromine have been studied by using a tubular reactor coupled to a photoionization mass spectrometer.The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm.The subsequent decays of the radical concentrations were monitored in time-resolved experiments as a function of Br2 concentration to obtain the rate constants of these Br-atom metathesis reactions.Rate constants were measured as a function of temperature to obtain Arrhenius parameters.The following rate constant expressions were obtained (units of the preexponential factor are cm³ molecule^-1 s^-1 and activation energies are kJ mol^-1; the temperature range covered in each study is also indicated): C2H3 + Br2 <(4.0 +/- 0.7)E-11 exp((2.4 +/- 1.5)/RT), 297-532 K>, C3H3 + Br2 <(2.8 +/- 0.5)E-12 exp((-2.3 +/- 1.2)/RT), 296-532 K>, and C3H5 +/- Br2 <(4.8 +/- 0.8)E-12 exp((1.6 +/- 0.8)/RT), 298-532 K>.The kinetics of R + Br2 reactions is reviewed, and the factors governing the reactivity of polyatomic free radicals in R + Br2 reactions are discussed.