Direct ring-open mechanism of pyridine formation by replacement of one carbon in benzene with one nitrogen atom

It is hardly replaced one carbon in benzene with other heteroatom by direct breaking of the particularly strong C=C bond in benzene not only due to the high dissociation energy of benzene ring but also due to more limit to the C–H activation. Direct ring-open of benzene has been mainly limited to the high dissociation energy. In our former research, we have found an ion-molecule reaction via simple replacement of one carbon in benzene with nitrogen atom. But the reaction mechanism still remains unresolved. Herein, we demonstrate the direct ring-open mechanism in benzene through theoretical study of potential energy surface, in which benzene attacked by H₂NO₂ ⁺ ion with the formation of pyridine. Reaction mechanisms have been confirmed that ring-open in benzene involves two steps that include attacking reaction and isomerization process. It is found that H₂NO₂ ⁺ ion trend to attack benzene with dissociation of H₂O firstly. The isomerization process happens is most favorable in the evolution potential energy surface of the isomer C₆H₅N(H)O⁺. It has been verified of the theory, which is consistent with the experiment. The mechanism derived from this study may provide guidance for promoting the reaction yield and selectivity of aromatics ring-open reaction.