The kinetics of ozonation of C,H, and C,H, have been studied in the gas phase from -40 to -95ยฐC (C,H,) and + I 0 to -30% (C,H,). The 0, concentrations were near M, and the hydrocarbons were present in 2-to 25-fold excess. A few experiments with propylene were also carried out. The reactions were followed by observing the rate of decay of 0, absorption at 2537 A. Reaction stoichiometries and effects of added 0, were investigated. The second-order rate constant for C,H, was log k(M-l sec-l) = (6.
). The rate was independent of the presence of excess 0,. Rate measurements for C,H, were less accurate because of aerosol interference. Combined with room temperature measurements of other workers, the C,H, rate constant was log k(M-l sec-l) = (6.0 f 0.4) -(3.2 f 0.6)/6. The C,H, rate constant was log k(W1-I sec-l) = (9.5
I n the case of C,H, the major product was propylene ozonide. Ethylene did not yield the ozonide, and the products of the 0,-C,H4 and 0,-C,H, reactions were not identified. Pre-exponential factors for the olefin reactions are consistent with a five-membered ring transition state formed by 1,3 dipolar cycloaddition of 0,. For C,H,, however, the much higher observed A factor suggests a different mechanism. Possible transition states for the 0,-C,H, reaction are discussed.
0.4) -(10.8 & 0.4)/6.