Complex Mechanism of the Gas Phase Reaction between Formic Acid and Hydroxyl Radical. Proton Coupled Electron Transfer versus Radical Hydrogen Abstraction Mechanisms

Abstract

The gas phase reaction between formic acid and hydroxyl radical has been investigated with high level quantum mechanical calculations using DFT-B3LYP, MP2, CASSCF, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets. The reaction has a very complex mechanism involving several elementary processes, which begin with the formation of a reactant complex before the hydrogen abstraction by hydroxyl radical. The results obtained in this investigation explain the unexpected experimental fact that hydroxyl radical extracts predominantly the acidic hydrogen of formic acid. This is due to a mechanism involving a proton coupled electron-transfer process. The calculations show also that the abstraction of formyl hydrogen has an increased contribution at higher temperatures, which is due to a conventional hydrogen abstraction radical type mechanism. The overall rate constant computed at 298 K is 6.24 x 10(-13) cm3 molecules(-1) s(-1), and compares quite well with the range from 3.2 +/- 1 to 4.9 +/- 1.2 x 10(-13) cm3 molecules(-1) s(-1), reported experimentally.

Photochemical aging of volatile organic compounds associated with oil and natural gas extraction in the Uintah Basin, UT, during a wintertime ozone formation event

“…Previous modeling has suggested that VOC reactions with other radicals, such as Cl q , were negligible in comparison to reactions with OH . Additionally, reaction rates of the primary species considered here (C6-C10 aromatics) with O 3 and NO 3 are at least several orders of magnitude lower than reaction rates with OH (Atkinson and Arey, 2003 Anglada (2004). All other OH rate constants from Atkinson and Arey (2003).…”

Ab initio and kinetic modeling studies of formic acid oxidation

“…The experimental results, including isotopic substitution, indicate that the hydroxyl radical at low temperatures abstracts predominantly the acidic hydrogen. This finding is unexpected because for HOCHO the bond strength of C-H is smaller than that of O-H [36]. Two theoretical studies [36,61] both indicate that (R8) dominates at room temperature, while (R7) becomes increasingly important at higher temperatures.…”

“…Anglada [36] calculated rate constants for (R7) and (R8) at temperatures up to 460 K, and we fitted his results to the form AT β exp(-B/T) for extrapolation to higher temperatures.…”

Coupling Interactions between Sulfurous Acid and the Hydroperoxyl Radical

“…On the one hand, the formation of radical-molecule complexes can considerably influence the kinetic behavior of many atmospheric reactions as well as the spread of contamination through the atmosphere and the formation of aerosols. [1,37] On the other hand, many stable H-bonded radical-molecule complexes associated with the HOO radical have been located, [7-8, 10, 38] although the HOO radical is an important species of atmospheric interest in the process of depletion of ozone layer. [39][40] Moreover, their larger binding energies can be comparable to those of systems bound through weak covalent bonds.…”