Interaction of NH2 radical with alkylbenzenes

Kamal Siddique, Mohammednoor Altarawneh, Anam Saeed, Zhe Zeng, Jeff Gore, Bogdan Z. Dlugogorski

Research output: Contribution to journalArticle

Abstract

Abstraction of a hydrogen atom from the alkyl side chain, attached to a benzene ring, by the amidogen radical (NH2), plays a critical importance in thermal processes that involve the presence of alkylbenzene species and NH2-containing species, as in the pyrolysis of biomass. Yet, literature provides no thermo-kinetic account of this important category of reactions. In this contribution, we compute standard reaction (Δr298) and activation enthalpies (Δ298) for H removal from the alkyl side chains in toluene, ethylbenzene and n-propylbenzene, as well as addition of NH2 at the four possible sites of the phenyl ring in toluene and ethylbenzene. Abstraction of the benzylic H atom in toluene constitutes the sole feasible channel at all temperatures. The same finding applies to ethylbenzene, albeit with a gradual increase of the contribution from the channel of abstraction of primary's H with increasing temperatures. The rate constant of the abstraction of benzylic H in n-propylbenzene dominates that of the primary and secondary H atoms. Computed branching ratios confirm the dominance of H abstraction corridors over the addition channels, even at low temperatures. For primary's H abstraction reactions, comparing reaction rate constants of alkylbenzenes with those of the analogous sites in alkanes indicates a noticable influence of the aromatic ring on the reaction rate constants. The results of the present calculations apply to any branched aromatic hydrocarbon interacting with the NH2 radical.

Original languageEnglish
Pages (from-to)85-96
Number of pages12
JournalCombustion and Flame
Volume200
Issue numberFebruary
Early online date23 Nov 2018
DOIs
Publication statusPublished - 1 Feb 2019
Externally publishedYes

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