Metal-free and iron(II)-assisted oxidation of cyclohexane to adipic acid with ozone: A theoretical mechanistic study

Adipic acid has a tremendous applied importance. Its industrial synthesis requires harsh conditions and application/emission of hazardous HNO3 and N2O. Here, a mechanism of ecologically benign neat cyclohexane (CyH) oxidation with ozone into adipic acid under room temperature and radiation-free conditions, both metal-free and catalyzed by the iron(II) complex [FeCl2{κ3-HC(pz)3}] (pz = pyrazol-1-yl), was investigated by theoretical methods. Relatively high activation barriers of the rate limiting H-abstractions by O3 without a catalyst explain the experimentally observed low CyH conversion and selectivity toward adipic acid due to efficient accumulation of cyclohexanone. The active catalytic form [FeIV(=O)Cl2{κ3-HC(pz)3}] improves both CyH conversion and selectivity because it is a much more efficient H-abstractor compared to O3 and provides facile decomposition of CyH and cyclohexanone, opens up a new route to the formation of ortho-cyclohexanediol and then adipic acid, and prevents the accumulation of adipic anhydride – one of the stable intermediates under metal-free conditions. © 2021 Elsevier Inc.

Authors
Kuznetsov M.L.1 , Pombeiro A.J.L. 1, 2
Publisher
Academic Press Inc.
Language
English
Pages
52-66
Status
Published
Volume
399
Year
2021
Organizations
  • 1 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa, 1049-001, Portugal
  • 2 Peoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Street, Moscow, 117198, Russian Federation
Keywords
Adipic acid; Alkanes; Cyclohexane; DFT calculations; Hydrocarbons; Iron complexes; Oxidation; Ozone; Reaction mechanism
Date of creation
20.07.2021
Date of change
20.07.2021
Short link
https://repository.rudn.ru/en/records/article/record/74181/
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