Development of a Group Contribution Method To Predict Aqueous Phase Hydroxyl Radical (HO•) Reaction Rate Constants

Abstract

The hydroxyl radical (HO*) is a strong oxidant that reacts with electron-rich sites of organic compounds and initiates complex chain mechanisms. In order to help understand the reaction mechanisms, a rule-based model was previously developed to predict the reaction pathways. For a kinetic model, there is a need to develop a rate constant estimator that predicts the rate constants for a variety of organic compounds. In this study, a group contribution method (GCM) is developed to predict the aqueous phase HO* rate constants for the following reaction mechanisms: (1) H-atom abstraction, (2) HO* addition to alkenes, (3) HO* addition to aromatic compounds, and (4) HO* interaction with sulfur (S)-, nitrogen (N)-, or phosphorus (P)-atom-containing compounds. The GCM hypothesizes that an observed experimental rate constant for a given organic compound is the combined rate of all elementary reactions involving HO*, which can be estimated using the Arrhenius activation energy, E(a), and temperature. Each E(a) for those elementary reactions can be comprised of two parts: (1) a base part that includes a reactive bond in each reaction mechanism and (2) contributions from its neighboring functional groups. The GCM includes 66 group rate constants and 80 group contribution factors, which characterize each HO* reaction mechanism with steric effects of the chemical structure groups and impacts of the neighboring functional groups, respectively. Literature-reported experimental HO* rate constants for 310 and 124 compounds were used for calibration and prediction, respectively. The genetic algorithms were used to determine the group rate constants and group contribution factors. The group contribution factors for H-atom abstraction and HO* addition to the aromatic compounds were found to linearly correlate with the Taft constants, sigma*, and electrophilic substituent parameters, sigma+, respectively. The best calibrations for 83% (257 rate constants) and predictions for 62% (77 rate constants) of the rate constants were within 0.5-2 times the experimental values. This accuracy may be acceptable for model predictions of the advanced oxidation processes (AOPs) performance, depending on how sensitive the model is to the rate constants.

Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

“…Kinetic data for aqueous phase reactions with OH are available or can be estimated based on structurereactivity-relationships (e.g. Ervens et al, 2003b;Herrmann, 2003;Monod et al, 2005;Monod and Doussin, 2008;Minakata et al, 2009;Herrmann et al, 2010). Most OH reactions with organic compounds are near the diffusion limit in the aqueous phase (k = 10 9 -10 10 M −1 s −1 ).…”

Structure–activity relationship for the estimation of OH-oxidation rate constants of carbonyl compounds in the aqueous phase

“…The resulting accuracy of this method was that 60 % of the estimated values were found within the range of 80 % of the experimental values (Monod and Doussin (2008)). Minakata et al (2009), using a similar group contribution approach, have proposed another structure-activity method concerning both H-abstraction and OH-addition on C = C double bonds. For saturated species, while this alternative relationship is applicable to a larger number of chemical families (as it includes ethers, esters, halides, nitrile, amines, amides, sulfides, sulfoxides, thiols, nitro compounds, nitroso compounds and phosphate-containing compounds, in addition to those modelled by Monod and Doussin, 2008), it involves only a parameterization using the α-position effect and no group contribution factor for k(OH) rate constants.…”

“…The value of the equilibrium constant K hyd can vary by several orders of magnitude dep 15 chemical structure of the considered molecule, while the reactivity towards OH can dif 16 of 3 from the carbonyl to the corresponding gem-diol form (Schuchmann and von Sonnt 17 combination of these two effects leads to major difficulties in the reliable parameter 18 constants which were often experimentally determined when both forms were co-existin 19 Minakata et al (2009) …”

“…The combination of these two effects leads to major difficulties in the reliable parameterization of rate constants which were often experimentally determined when both forms were co-existing. Minakata et al (2009) considered carbonyl bearing molecules either being totally hydrated (formaldehyde and glyoxal for which K hyd > 100) or totally non-hydrated (K hyd < 0.01), with an exception for acetaldehyde, which was treated in its two forms as its K hyd was known to be close to 1(K hyd, acetaldehyde = 1.2 at 298 K). However, K hyd is also intermediate for many other carbonyl compounds such as propionaldehyde, butyraldehyde, valeraldehyde, isobutyraldehyde, pyruvic acid, or biacetyl (see Table 1), which requires a careful OH-oxidation rate constant estimation for both forms to try to correlate estimated and experimental values.…”

Modeling the partitioning of organic chemical species in cloud phases with CLEPS (1.1)

“…In addition to the inorganic chemical scheme previously described in Deguillaume et al (2004) and in Leriche et al (2007), CLEPS 1.0 describes the HO q and NO 3 q oxidation pathways of C 1-4 organic compounds following the methodology developed by Mouchel-Vallon et al (2017). CLEPS 1.0 relies on recent improvements in the estimation of kinetic and thermodynamic parameters based on structure-activity relationships (SARs) derived from experimental data (Doussin and Monod, 2013;Minakata et al, 2009;Monod and Doussin, 2008;Raventos-Duran et al, 2010). Mouchel-Vallon and coworkers used these SARs (1) to derive the reaction rates or equilibrium constants of species that were not well documented in the literature and (2) to determine, for the first time, the branching ratios and further select the major oxidation pathways with HO q to be included in the mechanism.…”