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 (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.
| Original language | English |
|---|---|
| Pages (from-to) | 85-96 |
| Number of pages | 12 |
| Journal | Combustion and Flame |
| Volume | 200 |
| Issue number | February |
| Early online date | 23 Nov 2018 |
| DOIs | |
| Publication status | Published - 1 Feb 2019 |
| Externally published | Yes |
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Interaction of NH2 radical with alkylbenzenes. / Siddique, Kamal; Altarawneh, Mohammednoor; Saeed, Anam; Zeng, Zhe; Gore, Jeff; Dlugogorski, Bogdan Z.
In: Combustion and Flame, Vol. 200, No. February, 01.02.2019, p. 85-96.Research output: Contribution to journal › Article
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.
PY - 2019/2/1
Y1 - 2019/2/1
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
UR - http://www.scopus.com/inward/record.url?scp=85056861810&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2018.11.002
DO - 10.1016/j.combustflame.2018.11.002
M3 - Article
AN - SCOPUS:85056861810
VL - 200
SP - 85
EP - 96
JO - Combustion and Flame
JF - Combustion and Flame
SN - 0010-2180
IS - February
ER -