No abstract

The stable products of the low-pressure (4-8 torr (1 torr = 133.33 Pa)) gas-phase reactions of ozone with ethene, propene, 2-methylpropene, cis-2-butene, trans-2-butene, trans-2-pentene, 2,3-dimethyl-2-butene, and 2-ethyl-1 -butene have been identified by using a photoionization mass spectrometer coupled to a stirred-flow reactor. The products observed are characteristic of (i) a primary Criegee split to an oxoalkane (aldehyde or ketone) and a Criegee intermediate,of the Criegee intermediates such as unimolecular decomposition, secondary ozonide formation, etc., and (iii) secondary alkene chemistry involving OH and other free-radical products formed by the unimolecular decomposition of the Criegee intermediates. The secondary OHalkene412 reactions account for a significant fraction of the alkene ( C a b ) consumed and lead to characteristic products such as C, dioxoalkanes [R'C(O)C(O)R'', at m/e (C,Hb + 30)], C, acyloins [R'C(O)CH(OH)R", at m/e (C,H2, + 32)], and C, alkanediols [R'CH(OH)CH(OH)R", at m/e (C,H2, + 34)]. C, oxoalkanes and C, epoxyalkanes observed at m/e (C,H2, + 16) are probably formed primarily via epoxidation of the alkene by 03. A general mechanism has been proposed to account for the observations.There is considerable evidencel-10 that the gas-phase reactions of ozone with alkenes can be described, at least in part, by the Criegee mechanism shown in eq 1 and 2 for solution-phase ozo-

CH3)C(=0)CH2' radical as well as the accompanying HO' radical was formed in the 03-TME system via reaction 5.To further examine the oxidation of CH3C(=0)CH2' radicals, the photolysis of mixtures containing parts-per-million concentrations of Cl2 and (CH3)2C=0 in air yielded methylglyoxal H3C(=0)CH0 as a major product, i.e., ca. 30% of A-[(CH3)2C=0], which can be attributed to the oxidation of the CH3C(=0)CH2' radical. Thus, the observation of CH3C(= OjCHO in the 03-TME-02 system (cf. Tables I and II) is consistent with the formation of this radical via reaction 5. A plausible mechanism for the formation of CH3C(=0)CH0 is CH3C(=0)CH2' 4-02 -CH3C(=0)CH200'; 2CH3C(=0)-CH200' -2CH3C(=0)CH20' 4-02; and CH3C(=0)CH20' 4-02 -* CH3C(=0)CH0 4-HOO'. Under atmospheric conditions, CH3C(=0)CH20' may react predominantly with 02 rather than undergoing unimolecular dissociation to CH3CO" and HCHO.12 No further quantitative determination of these competing reactions was pursued in the present study. Instead, at-tention was focused on the detection of a carbonyl product arising from the reaction CH3C(=0)CH200' 4-HOO* -CH3C(= 0)CH2OOH 4-02, since this compound was suspected to be the unidentified species exhibiting the C=0 band at ca. 1740 cm'1 in the 03-TME reaction (cf. Figure 2C). A broad band in this

Steady state concentrations of formyl radicals were measured with a photoionization mass spectrometer. The reaction of ethylene with oxygen atoms in a system free of OCHO+Oas was suggested by Groth and coworkers in 1938. The rate constant for this reaction was calculated to be (5.7±1.2)×10

The chemistry and energetics of the Criegee intermediate, a primary product of the ozonolysis of alkenes, are discussed in terms of recent ab-initio calculations and laboratory studies. The experimental observations in 03-alkene systems can be rationalized on the basis of a general mechanism:

No abstract

The autoinhibiting reaction of ozone with dimethyl sulfide (DMS),(1) DMS + 03 -products has been studied at 296°K and 1.1 kPa (8 torr) as a function of the concentrations of both reactants. The major products of the reaction are H&O, HzO, CO, and SOz. The specific rate of primary attack of O3 on DMS is immeasurably slow. It is suggested that the rapid overall rate observed for this reaction is due to a chain reaction initiated by the very slow primary reaction. It is concluded that reaction (1) cannot be important under atmospheric conditions and that the major loss process for DMS in the atmosphere is probably reaction with photochemically generated free radicals.

A reaction scheme is proposed to explain the H 2 SO 4 aerosol formation experimentally observed in O 3 -alkene-SO 2 systems in terms of adduct formation between SO 2 and a Criegee intermediate.The reaction scheme also provides the basis for a homogeneous gas-phase flue-gas desulfurízatíon process.