Ozone Reactions with Olefins and Alkynes: Kinetics, Activation Energies, and Mechanisms.

The temperature dependence of the kinetics and the mechanisms of ozone reactions with 19 olefins and 3 alkynes were investigated. The second-order rate constants (k(O(3))) for ozone reactions with olefins were mostly in the range of 10(3)-10(6) M(-1) s(-1), with activation energies of 17.4-37.7 kJ mol(-1). In comparison, alkynes had lower k(O(3)) (∼10(2) M(-1) s(-1)) and higher activation energies (36.7-48.1 kJ mol(-1)). Reactivities of both olefins and alkynes are mainly influenced by inductive effects of substituents, with steric effects observed for cyclic olefins. 2-Buten-1,4-dial (BDA), synthesized with a novel method, is a toxic olefinic oxidation product from phenols. Its cis- and trans-isomers show distinct reactivities with ozone, with k(O(3)) (20 °C) of 3.0 × 10(3) and 1.2 × 10(4) M(-1) s(-1), respectively. Two mols of glyoxal were formed per mol of ozonated BDA, with a slow release of the second mol from an α-hydroxyalkylhydroperoxide intermediate. 2-Ethynylbenzaldehyde reacts with ozone with a stoichiometry of 1:1 and k(O(3)) (20 °C) = 1.6 × 10(2) M(-1) s(-1). Ozone attacks the ethynyl group, yielding a carboxyl product (2-carboxybenzaldehyde, 54%), an aldehyde product (phthaldialdehyde), and a dicarbonyl product with a stoichiometric release of H(2)O(2) (21%). This study provides kinetic and mechanistic information for assessing the abatement of olefin- and alkyne-containing micropollutants by ozonation at various temperatures.