Ozone Reactions with Olefins and Alkynes: Kinetics, Activation Energies, and Mechanisms
Yan Wang, Eva M. Rodrı́guez, Daniel Rentsch, Zhimin Qiang, Urs von Gunten
Abstract
High Resolution Image Download MS PowerPoint Slide 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.