The mechanism of electrophilic addition of singlet oxygen to pyrrolic ring

Nassim Zeinali, Ibukun Oluwoye, Mohammednoor Altarawneh, Bogdan Z. Dlugogorski

Research output: Contribution to journalArticle

Abstract

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 (O21g) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels–Alder addition of O21g 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.

Original languageEnglish
Article number90
Pages (from-to)1-11
Number of pages11
JournalTheoretical Chemistry Accounts
Volume138
Issue number7
Early online date11 Jun 2019
DOIs
Publication statusPublished - Jul 2019
Externally publishedYes

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