Theoretical investigation of the ethylbenzene with NH₂ radical: H abstraction and addition reactions pathways

Thermal processes like pyrolysis of biomass and coal account for the interaction of alkylbenzenes with amidogen (NH₂) radical. The NH₂ radical evolves from the oxidation of ammonia and hydrogen cyanide in processes encompassing the transformation of nitrogenous fuels, with significant propositions to atmospheric and combustion systems. In this study, for the first time, we investigate the gas-phase mechanisms governing the reactions of ethylbenzene, as modelled alkylbenzene species, with NH₂ radical. More specifically, we determine H abstractions and addition reactions of ethylbenzene with NH₂. We compute standard reaction (Δ_rHº₂₉₈) and activation (ΔHº₂₉₈) enthalpies for H removal from the alkyl side chains (primary H and benzylic H) in ethylbenzene, as well as the addition of NH₂ at the four possible sites (ipso, ortho, meta and para) of the ethylbenzene phenyl ring. The kinetic analysis of the interaction of ethylbenzene with NH₂ shows that abstraction of benzylic H atom represents the exclusive plausible corridor at all temperatures. The computed mechanistic and kinetic parameters (fitted in the temperature range of 300-2000 K) entail high accuracy level and corroborate with the available literature measurements.