TY - JOUR
T1 - Interaction of NH2 radical with alkylbenzenes
AU - Siddique, Kamal
AU - Altarawneh, Mohammednoor
AU - Saeed, Anam
AU - Zeng, Zhe
AU - Gore, Jeff
AU - Dlugogorski, Bogdan Z.
N1 - Funding Information:
This study was funded by the Australian Research Council (ARC) and Asia Pacific, and was supported by grants of computing time from the National Computational Infrastructure (NCI), Canberra, Australia and the Pawsey Supercomputing Centre, Perth, Australia. K. S. thanks Murdoch University for the award of a postgraduate scholarship.
Publisher Copyright:
© 2018 The Combustion Institute
PY - 2019/2
Y1 - 2019/2
N2 - 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 (ΔrH°298) and activation enthalpies (Δ⧧H°298) 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.
AB - 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 (ΔrH°298) and activation enthalpies (Δ⧧H°298) 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.
KW - Amidogen radical (NH)
KW - Aromatic hydrocarbon
KW - Bond dissociation enthalpies
KW - Reaction rate constants
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U2 - 10.1016/j.combustflame.2018.11.002
DO - 10.1016/j.combustflame.2018.11.002
M3 - Article
AN - SCOPUS:85056861810
SN - 0010-2180
VL - 200
SP - 85
EP - 96
JO - Combustion and Flame
JF - Combustion and Flame
ER -