New Pathways for Formation of Acids and Carbonyl Products in Low-Temperature Oxidation: The Korcek Decomposition of γ-Ketohydroperoxides
| Autor: | Shamel S. Merchant, William H. Green, Rubén Meana-Pañeda, Amrit Jalan, Ke R. Yang, I. M. Alecu, Donald G. Truhlar, Jorge Aguilera-Iparraguirre |
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| Rok vydání: | 2013 |
| Předmět: |
Exothermic reaction
chemistry.chemical_classification Carboxylic acid General Chemistry Kinetic energy Combustion Biochemistry Peroxide Catalysis Dissociation (chemistry) Homolysis chemistry.chemical_compound Colloid and Surface Chemistry chemistry Ab initio quantum chemistry methods Physical chemistry Physics::Chemical Physics |
| Zdroj: | Journal of the American Chemical Society. 135:11100-11114 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja4034439 |
| Popis: | We present new reaction pathways relevant to low-temperature oxidation in gaseous and condensed phases. The new pathways originate from γ-ketohydroperoxides (KHP), which are well-known products in low-temperature oxidation and are assumed to react only via homolytic O-O dissociation in existing kinetic models. Our ab initio calculations identify new exothermic reactions of KHP forming a cyclic peroxide isomer, which decomposes via novel concerted reactions into carbonyl and carboxylic acid products. Geometries and frequencies of all stationary points are obtained using the M06-2X/MG3S DFT model chemistry, and energies are refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. Thermal rate coefficients are computed using variational transition-state theory (VTST) calculations with multidimensional tunneling contributions based on small-curvature tunneling (SCT). These are combined with multistructural partition functions (Q(MS-T)) to obtain direct dynamics multipath (MP-VTST/SCT) gas-phase rate coefficients. For comparison with liquid-phase measurements, solvent effects are included using continuum dielectric solvation models. The predicted rate coefficients are found to be in excellent agreement with experiment when due consideration is made for acid-catalyzed isomerization. This work provides theoretical confirmation of the 30-year-old hypothesis of Korcek and co-workers that KHPs are precursors to carboxylic acid formation, resolving an open problem in the kinetics of liquid-phase autoxidation. The significance of the new pathways in atmospheric chemistry, low-temperature combustion, and oxidation of biological lipids are discussed. |
| Databáze: | OpenAIRE |
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