FORMATION OF C3H6 FROM THE REACTION C3H7-2 BETWEEN 450 AND 550 K(O)

The generation of C3H6 from the reaction C3H7 + O-2 (1) has been inves tigated as a function both of temperature (450-550 K) at constant dens ity (5.5 x 10(18) molecules/cm(3)) and of pressure (55-550 Torr) at 49 0 K. The experiments were carried out by UV irradiation of mixtures of C3H8, Cl-2, and O-2 to generate propyl radicals. C3H8, C3H6, and C3H7 Cl were monitored by gas chromatographic analysis. The propylene yield is 0.7% at 450 K. Based on these measurements and previous data at 29 8 K, the propylene yield has; an apparent activation energy which is l ess than 2.5 kcal mol(-1) below 450 K. Beginning near 450 K, the yield increases rapidly with an apparent activation energy of similar to 32 kcal mol(-1), similar to previous observations on the generation of C 2H4 from the reaction C2H5 + O-2. At 490 K, the propylene yield from r eaction 1 depends inversely on total pressure (Y-C3H6 proportional to P-0.6) between 55 and 550 Torr, while the overall value of k(1) has a much smaller pressure dependence (P-0.18). These observations show tha t above 450 K propylene is formed via reaction 1 through an excited pr opylperoxy adduct which can be stabilized by collision as was observed at 298 K.