Mechanism for the Gas-Phase Reaction between Formaldehyde and Hydroperoxyl Radical. A Theoretical Study

Abstract

We present a high-level theoretical study on the gas-phase reaction between formaldehyde and hydroperoxyl radical carried out using the DFT-B3LYP, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311+G(d,p), 6-311+G(2df,2p), and aug-cc-pVTZ basis sets. The most favorable reaction path begins with the formation of a pre-reactive complex and produces the peroxy radical CH(2)(OO)OH in a process that is computed to be exothermic by 16.8 kcal/mol. This reaction involves a process in which the oxygen terminal of the HO(2) moiety adds to the carbon of formaldehyde, and, simultaneously, the hydrogen of the hydroperoxyl group is transferred to the oxygen of the carbonyl in a proton-coupled electron-transfer mechanism. Our calculations show that this transition state lies below the sum of the energy of the reactants, and we computed a rate constant at 300 K of 9.29 x 10(-14) cm(3) molecule(-1) s(-1), which is in good agreement with the experimental results. Also of interest in combustion chemistry, we studied the hydrogen abstraction process by HO(2), the result of which is the formation of HCO + H(2)O(2). We found two reaction paths with activation enthalpies close to 12 kcal/mol. For this process, we computed a rate constant of 1.48 x 10(-16) cm(3) molecule(-1) s(-1) at 700 K, which also agrees quite well with experimental results.

Theoretical study on HO2‐initiated atmospheric oxidation of halogenated carbonyls

“…Table 2 and 3 give the selected geometrical parameters of the reactants, and prereactive complexes, transition states, and products, respectively. From Table 1, the binding energy of the complex C1 is found to be -6.59 kcal/mol, which is lower than the counterpart in the HO 2 þ HCHO reaction [17] by 1.00 kcal/mol and approximately equals with the values relative to the glyoxal with HO 2 reaction at the G3SX level of theory [19]. Additionally, the activated barrier (0.13 kcal/mol) is about 2.00 kcal/mol higher than the corresponding reactions of HO 2 with HCHO [17] and glyoxal [19], revealing that the rate constant of the HO 2 þ ClC(O)-C(O)Cl is 1-2 orders slower than those of the reactions of HO 2 with HCHO, and glyxoal, respectively.…”

“…For simplicity, as the reported energies are of the most relevance, the comparison is focused on these energy values relative to the reaction of HO 2 with HCHO, especially the activated barrier. In addition, Anglada and Domingo [17] has shown that the dominant reaction pathway is characterized as the proton transfer coupled electron transfer that the H of HO 2 is transferred to the oxygen atom of HCHO, simultaneously the terminal oxygen of HO 2 atom is added to the carbon atom of the carbonyl group in HCHO and the electron transfer occurred between two oxygen atoms of HO 2 . Thus, these values are represented here with respect to the most favorable reaction path for the HO 2 þ HCHO reaction and provided in Supporting Information Tables S1, S2, and S3.…”

“…For example, the reaction mechanisms and kinetics of HO 2 with ozone [5][6][7][8][9][10][11][12][13][14][15] have been extensively investigated as it has a key role in ozone depletion. The HO 2 radical reacts with carbonyls and acetone [16][17][18][19][20], which have been studied. In addition, the kinetic data from the reactions of HO 2 with alcohol substances and organic peroxy radicals has been reported [21][22][23][24][25][26][27] in the literature.…”

Ab initio and kinetic modeling studies of formic acid oxidation

“…In general, at low temperatures we might expect the oxygencontaining species here to be stabilized by hydrogen bonding to water or formic acid, which may lead to enhanced reactivity under conditions associated with atmospheric chemistry [52,53], but these interactions will likely not be important under combustion conditions and so are not considered further here. The reaction of HO 2 with CH 2 O proceeds via reversible addition across the C=O group, with no overall barrier, to yield HOCH 2 OO [55].…”

Isoprene oxidation mechanisms: measurements and modelling of OH and HO<sub>2</sub> over a South-East Asian tropical rainforest during the OP3 field campaign

“…Although we find that the modelled concentrations of hydroxyacetone (ACETOL in Table 4) are sufficient for it to be considered a candidate for X, the main fate of the α-hydroxyperoxy radicals formed on interaction of such carbonyl species with HO 2 at the temperatures encountered during OP3 is expected to be dissociation back to HO 2 and the carbonyl species. Introduction of a non-reversible reaction in the model between hydroxyacetone and HO 2 to produce CH 3 C(O)OOH, HCHO and OH (the α-hydroxyperoxy radical decomposition products predicted by da Silva, 2011) with a rate coefficient of k = 1×10 −10 cm 3 s −1 and between hydroxyacetone and RO 2 to produce HO 2 with a rate coefficient of k = 2.46×10 −12 cm 3 s −1 did little to improve the model success (observed to modelled ratios for isoprene impacted points of 5.06 HCHO was also considered as a potential contender for the species X, and is known to form an adduct with HO 2 Burrows et al, 1989;Anglada and Domingo, 2005). However, since HCHO provides a photolytic source of HO x , a model run including reactions of HCHO with RO 2 to produce HO 2 and with HO 2 to produce OH reduces the modelled HCHO concentration and thus the HO x production from HCHO photolysis, and does not provide a solution.…”