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The mechanism of electrophilic addition of singlet oxygen to pyrrolic ring

Zeinali, N., Oluwoye, I.ORCID: 0000-0002-0221-020X, Altarawneh, M.ORCID: 0000-0002-2832-3886 and Dlugogorski, B.Z. (2019) The mechanism of electrophilic addition of singlet oxygen to pyrrolic ring. Theoretical Chemistry Accounts, 138 (7).

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Pyrrolic compounds assume an important role in the chemistry of living organisms, coal surrogates and novel drugs. However, literature reports a few studies on their reactivity towards prominent oxidising agents. This contribution presents a comprehensive mechanistic study of the oxidation of unsubstituted pyrrole with singlet oxygen (O2 1∆g) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels–Alder addition of O2 1∆g to the aromatic ring. Other products such as maleimide, hydroperoxide, formamide and epoxide adducts appear to form via insignificant channels. The primary Diels–Alder channel encompasses a barrier of 41 kJ/mol with a fitted rate constant of k(T) = 1.87 × 10−13 exp(− 48,000/RT) cm3 mol−1 s−1. Furthermore, a kinetic study has been undertaken to investigate the influence of substituents on reaction rate of the Diels–Alder addition of singlet oxygen to a pyrrolic ring. The results clarify that electropositive substituents such as BeH and BH2 operate as π-acceptors and thus deactivate the ring towards electrophilic attack of singlet oxygen. However, substituents comprising of strong π-donors, e.g., NH2 and OH, destabilise the ring structure, increasing its oxidation reactivity.

Item Type: Journal Article
Murdoch Affiliation(s): Engineering and Energy
Publisher: Springer New York
Copyright: © 2019 Springer-Verlag GmbH Germany, part of Springer Nature
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