FORMATION OF C3H6 FROM THE REACTION C3H7-2 AND C2H3CL FROM C2H4CL+O-2AT 297 K(O)

The generation of conjugate olefins from the reactions of propyl (reac tion 1) chloroethyl (reaction 2) radicals with O-2 has been investigat ed as a function of total pressure (0.4-700 Torr) at 297 +/- 2 K. The experiments were carried out by UV irradiation of mixtures of propane (or ethyl chloride), Cl-2, and O-2 to generate alkyl radicals. Propyle ne from reaction 1 was measured by FTIR spectroscopy, while vinyl chlo ride from reaction 2 was monitored by both FTIR and gas chromatographi c analysis. At pressures where the formation of propylperoxy radicals is near the high-pressure limit, the propylene yield from reaction 1 w as inversely dependent on total pressure (Y-C3H6 proportional to P--0. 68+/-0.03), providing that it is formed via rearrangement of an excite d propylperoxy adduct that can also be stabilized by collision. The vi nyl chloride yield decreased from 0.3 +/- 0.1% at 1 Torr to <0.1% at 1 0 Torr. Because the formation of chloroethylperoxy radicals is in the fall-off region over this pressure range, the vinyl chloride yield can not be ascribed unambiguously to an addition-elimination process. The propylene yield from reaction 1 is 2-4 times smaller than the ethylene yield from C2H5 + O-2 over the pressure range 0.4-100 Torr, while the vinyl chloride yield from reaction 2 is 40 times smaller between 1 an d 10 Torr. This is consistent with more efficient stabilization of the excited propylperoxy relative to the ethylperoxy adduct caused by the presence of additional vibrational modes, The markedly smaller ambien t temperature vinyl chloride yield from reaction 2 may result from a c ombination of more efficient stabilization resulting from the lower fr equency of the C-Cl bond and reduction of the C-H bond reactivity upon Cl substitution.