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 |
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Pages (from-to) | 85-96 |
Number of pages | 12 |
Journal | Combustion and Flame |
Volume | 200 |
DOIs | |
Publication status | Published - Feb 2019 |
Externally published | Yes |
Keywords
- Amidogen radical (NH)
- Aromatic hydrocarbon
- Bond dissociation enthalpies
- Reaction rate constants
ASJC Scopus subject areas
- General Chemistry
- General Chemical Engineering
- Fuel Technology
- Energy Engineering and Power Technology
- General Physics and Astronomy