The reactions of OH radicals with di-i-propoxymethane and di-sec-butoxymethane: Kinetic measurements and structure activity relationships

Abstract

The gas-phase reactions of OH(X²Π) radicals with di-i-propoxymethane (DiPM) and di-sec-butoxymethane (DsBM) have been studied in argon in the temperature range 295–700 K at total pressures between 50 and 400 Torr. OH radicals were generated by excimer laser photolysis of H₂O₂ and were detected by laser-induced fluorescence. Within the investigated ranges, the reactions of OH(X²Π) radicals with DiPM and DsBM were found to be independent of total pressure. Weak dependencies of the rate coefficients on temperature were observed. Bimolecular rate coefficients for the reactions of OH(X²Π) with DiPM and DsBM at 298 K of k_OH+DiPM=(3.47±0.20)×10^-11 cm³ s^-1 and k_OH+DsBM=(4.25±0.13)×10^-11 cm³ s^-1, respectively, have been determined. In order to describe the kinetics of the reactions of OH radicals with DiPM and DsBM as well as analogous acetals, a structure activity relationship (SAR) technique established for other reactant classes has been modified and applied. Compared to the former SAR method, which does not yield satisfying results for oxygenated VOCs (volatile organic compounds), the present calculations lead to much better agreement with the experimental data for dialkylacetals of the type R–O–CH₂–O–R.