Kinetic and reactivity of gas-phase reaction of acyclic dienes with hydroxyl radical in the 273–318 K temperature range

Abstract

As dienes contain two CC bonds, theoretically, they are much more chemically reactive with hydroxyl radical (˙OH) than alkenes and alkanes, and the reaction with ˙OH is one of the main atmospheric degradation routes of dienes during the daytime. In our work, rate coefficients of three types of acyclic dienes: conjugated as 3-methyl-1,3-pentadiene (3M13PD), isolated as 1,4-hexadiene (14HD), and cumulated as 1,2-pentadiene (12PD) reaction with ˙OH were measured in the temperature range of 273–318 K and 1 atm using the relative rate method. At 298 ± 3 K, the rate coefficients for those reactions were determined to be k_3M13PD+OH = (15.09 ± 0.72) × 10⁻¹¹, k_14HD+OH = (9.13 ± 0.62) × 10⁻¹¹, k_12PD+OH = (3.34 ± 0.40) × 10⁻¹¹ (as units of cm³ per molecule per s), in the excellent agreement with values of previously reported. The first measured temperature dependence for 3M13PD, 14HD and 12PD reaction with ˙OH can be expressed by the following Arrhenius expressions in units of cm³ per molecule per s: k_3M13PD+OH = (8.10 ± 2.23) × 10⁻¹¹ exp[(173 ± 71)/T]; k_14HD+OH = (9.82 ± 5.10) × 10⁻¹² exp[(666 ± 123)/T]; k_12PD+OH = (1.13 ± 0.87) × 10⁻¹² exp[(1038 ± 167)/T] (as units of cm³ per molecule per s). The kinetic discussion revealed that the relative position between these two CC could significantly affect the reactivity of acyclic dienes toward ˙OH. A simple structure–activity relationship (SAR) method was proposed to estimate the reaction rate coefficients of acyclic dienes with ˙OH.