Kinetics of α-Hydroxy-alkylperoxyl Radicals in Oxidation Processes. HO<sub>2</sub><sup>•</sup>-Initiated
Oxidation of Ketones/Aldehydes near the Tropopause
Ive Hermans
Jean-François Müller
Thanh Lam Nguyen
Pierre A. Jacobs
Jozef Peeters
10.1021/jp044080v.s001
https://acs.figshare.com/articles/journal_contribution/Kinetics_of_Hydroxy_alkylperoxyl_Radicals_in_Oxidation_Processes_HO_sub_2_sub_sup_sup_Initiated_Oxidation_of_Ketones_Aldehydes_near_the_Tropopause/3285442
A comparative theoretical study is presented on the formation and decomposition of α-hydroxy-alkylperoxyl
radicals, Q(OH)OO<sup>•</sup> (Q = RR‘C<b>:</b>), important intermediates in the oxidation of several classes of oxygenated
organic compounds in atmospheric chemistry, combustion, and liquid-phase autoxidation of hydrocarbons.
Detailed potential energy surfaces (PESs) were computed for the HOCH<sub>2</sub>O<sub>2</sub><sup>•</sup> ⇌ HO<sub>2</sub><sup>•</sup> + CH<sub>2</sub>O reaction and
its analogues for the alkyl-substituted RCH(OH)OO<sup>•</sup> and R<sub>2</sub>C(OH)OO<sup>•</sup> and the cyclic <i>cyclo</i>-C<sub>6</sub>H<sub>10</sub>(OH)OO<sup>•</sup>.
The state-of-the-art ab initio methods G3 and CBS-QB3 and a nearly converged G2M//B3LYP-DFT variant
were found to give quasi-identical results. On the basis of the G2M//B3LYP-DFT PES, the kinetics of the
≈15 kcal/mol endothermal α-hydroxy-alkylperoxyl decompositions and of the reverse HO<sub>2</sub><sup>•</sup> + ketone/aldehyde
reactions were evaluated using multiconformer transition state theory. The excellent agreement with the available
experimental (kinetic) data validates our methodologies. Contrary to current views, HO<sub>2</sub><sup>•</sup> is found to react as
fast with ketones as with aldehydes. The high forward and reverse rates are shown to lead to a fast Q(OH)OO<sup>•</sup> ⇌ HO<sub>2</sub><sup>•</sup> + carbonyl quasi-equilibrium. The sizable [Q(OH)OO<sup>•</sup>]/[carbonyl] ratios predicted for
formaldehyde, acetone, and <i>cyclo-</i>hexanone at the low temperatures (below 220 K) of the earth's tropopause
are shown to result in efficient removal of these carbonyls through fast subsequent Q(OH)OO<sup>•</sup> reactions with
NO and HO<sub>2</sub><sup>•</sup>. IMAGES model calculations indicate that at the tropical tropopause the HO<sub>2</sub><sup>•</sup>-initiated oxidation
of formaldehyde and acetone may account for 30% of the total removal of these major atmospheric carbonyls,
thereby also substantially affecting the hydroxyl and hydroperoxyl radical budgets and contributing to the
production of formic and acetic acids in the upper troposphere and lower stratosphere. On the other hand, an
RRKM−master equation analysis shows that hot α-hydroxy-alkylperoxyls formed by the addition of O<sub>2</sub> to
C<sub>1</sub>-, C<sub>2</sub>-, and C<sub>3</sub>-α-hydroxy-alkyl radicals will quasi-uniquely fragment to HO<sub>2</sub><sup>•</sup> plus the carbonyl under all
atmospheric conditions.
2005-05-19 00:00:00
G 2M variant
RR
multiconformer transition state theory
ab initio methods G 3
OH
data validates
HO
220 K
energy surfaces
C 6 H 10
carbonyl
Oxidation Processes
G 2M PES
O 2
RRKM
RCH
IMAGES model calculations
HOCH
cyclic cyclo
Initiated Oxidation
CH 2 O reaction
acetic acids