Issue 2, 2022

Decomposition mechanism of α-alkoxyalkyl-hydroperoxides in the liquid phase: temperature dependent kinetics and theoretical calculations

Abstract

Organic hydroperoxides (ROOHs) play key roles in the atmosphere as a reactive intermediate species. Due to the low volatility and high hydrophilicity, ROOHs are expected to reside in atmospheric condensed phases such as aerosols, fogs, and cloud droplets. The decomposition mechanisms of ROOHs in the liquid phase are, however, still poorly understood. Here we report a temperature-dependent kinetics and theoretical calculation study of the aqueous-phase decompositions of C12 or C13 α-alkoxyalkyl-hydroperoxides (α-AHs) derived from ozonolysis of α-terpineol in the presence of 1-propanol, 2-propanol, and ethanol. We found that the temporal profiles of α-AH signals, detected as chloride-adducts by negative ion electrospray mass spectrometry, showed single-exponential decay, and the derived first-order rate coefficient k for α-AH decomposition increased as temperature increased, e.g., k(288 K) = (5.3 ± 0.2) × 10−4 s−1, k(298 K) = (1.2 ± 0.3) × 10−3 s−1, k(308 K) = (2.1 ± 1.4) × 10−3 s−1 for C13 α-AHs derived from the reaction of α-terpineol Criegee intermediates with 1-propanol in the solution at pH 4.5. Arrhenius plot analysis yielded an activation energy (Ea) of 12.3 ± 0.6 kcal mol−1. Ea of 18.7 ± 0.3 and 13.8 ± 0.9 kcal mol−1 were also obtained for the decomposition of α-AHs (at pH 4.5) derived from the reaction of α-terpineol Criegee intermediates with 2-propanol and with ethanol, respectively. Based on the theoretical kinetic and thermodynamic calculations, we propose that a proton-catalyzed mechanism plays a central role in the decomposition of these α-AHs in acidic aqueous organic media, while water molecules may also participate in the decomposition pathways and affect the kinetics. The decomposition of α-AHs could act as a source of H2O2 and multifunctionalized species in atmospheric condensed phases.

Graphical abstract: Decomposition mechanism of α-alkoxyalkyl-hydroperoxides in the liquid phase: temperature dependent kinetics and theoretical calculations

Supplementary files

Article information

Article type
Paper
Submitted
27 sep 2021
Accepted
17 jan 2022
First published
17 jan 2022
This article is Open Access
Creative Commons BY license

Environ. Sci.: Atmos., 2022,2, 241-251

Decomposition mechanism of α-alkoxyalkyl-hydroperoxides in the liquid phase: temperature dependent kinetics and theoretical calculations

M. Hu, K. Chen, J. Qiu, Y. Lin, K. Tonokura and S. Enami, Environ. Sci.: Atmos., 2022, 2, 241 DOI: 10.1039/D1EA00076D

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