Acetonyl Peroxy and Hydro Peroxy Self- and Cross-Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product

Abstract

Pulsed laser photolysis coupled with infrared (IR) wavelength modulation spectroscopy and ultraviolet (UV) absorption spectroscopy was used to study the kinetics and branching fractions for the acetonyl peroxy (CH3C(O)CH2O2) self-reaction and its reaction with hydro peroxy (HO2) at a temperature of K and pressure of 100 Torr. Near-IR and mid-IR lasers simultaneously monitored HO2 and hydroxyl, OH, respectively, while UV absorption measurements monitored the CH3C(O)CH2O2 concentrations. The overall rate constant for the reaction between CH3C(O)CH2O2 and HO2 was found to be (5.5 ± 0.5) × 10-12 cm 3 molecule-1 s-1 and the branching fraction for OH yield from this reaction was directly measured as 0.30 ± 0.04. The CH3C(O)CH2O2 self-reaction rate constant was measured to be (4.8 ± 0.8) × 10-12 cm 3 molecule-1 s-1 and the branching fraction for alkoxy formation was inferred from secondary chemistry as 0.33 ± 0.13. An increase in the rate of the HO2 self-reaction was also observed as a function of acetone (CH3C(O)CH3) concentration which is interpreted as a chaperone effect resulting from hydrogen-bond complexation between HO2 and CH3C(O)CH3. The chaperone enhancement coefficient for CH3C(O)CH3 was determined to be k²A = (4.0 ± 0.2) ´ 10-29 cm 6 molecule-2 s-1 and the equilibrium constant for HO2•CH3C(O)CH3 complex formation was found to be Kc(R15) = (2.0 ± 0.89) × 10-18 cm 3 molecule-1 ; from these values the rate constant for the HO2 + HO2•CH3C(O)CH3 reaction was estimated to be (2 ± 1) × 10-11 cm 3 molecule-1 s-1. Results from UV absorption cross-section measurements of CH3C(O)CH2O2 and prompt OH radical yields arising from possible oxidation of the CH3C(O)CH3-derived alkyl radical are also discussed. Using theoretical methods, no likely pathways for the observed prompt OH radical formation have been found and thus remains unexplained.

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms

“…• Graph c shows the simulation using the rate constant and branching ratio as currently recommended by IUPAC: 5 k 1 is slightly faster than the current value, but the branching ratio is very similar (Table 1 , measured simultaneously over a large range of initial concentrations, a rate constant for the selfreaction of k 1 = (5.4 ± 1.4) × 10 −12 cm 3 s −1 has been obtained, in good agreement with a recent publication. 13 The branching ratio for the radical path, however, was found with ϕ 1b = (0.6 ± 0.1) well above the most recently published value (0.33 ± 0.13). This is a large disagreement because the branching ratio of the radical path has a strong influence on the profiles of the different species, and thus the agreement on the rate constant between both works, obtained with different branching ratios, must be fortuitous.…”

“…Figure 4d shows the HO 2 concentration−time profiles, which turned out to be very sensitive to (18a−18c). Very rapid HO 2 formation is observed under all conditions, and a strong increase 13 finds an equilibrium constant of K c = (1.4 ± 0.8) × 10 −18 cm −3 molecule −1 , which is around 10 and 500 times smaller than the corresponding equilibrium constants for CH 3 CHO and CH 2 O, respectively. 36 The establishment of the equilibrium is rapid, thus resulting in an overall reduced HO 2 concentration profile.…”

“…The branching ratio has been measured three times for the radical channel (1b), and no agreement is found with values varying between (0.75 ± 0.1), 11 (0.50 ± 0.05), 15 and (0.33 ± 0.13). 13 The branching fraction for (1c) has been inferred once 16 to be ϕ 1c = 0.16 by measuring the rate constant of the product appearance for channel (1c). The currently available literature data, together with the results obtained in this work, are summarized in Table 1.…”

Degradation Kinetics and Pathways of Isopropyl Alcohol by Microwave-Assisted Oxidation Process

“…Proposed degradation pathways of IPA in the MW/H 2 O 2 process, considering the identified acetone and carboxylic acid byproducts, aldehydes, and radical species suggested in the literature. ,,,, …”

Computational Study on the Reaction of β-Hydroxyethylperoxy Radical with HO2 and Effects of Water Vapor

“…There have been a number of experimental and computational studies on reactions between RO 2 and HO 2 . − Branching ratios of product channels change with the functional groups in −R. For the alkyl peroxy radicals, the reactions go through almost exclusively the R1a channel; while for the acyl and acetonyl peroxy radicals, the R1c channel becomes more significant.…”