Gas-phase amination of aromatic hydrocarbons by corona discharge-assisted nitrogen fixation

This paper reports on the gas-phase amination reaction of aromatic hydrocarbons occurring under corona discharge conditions with N₂ gas as the nitrogen source. The corona discharge device within an atmospheric pressure chemical ionization source was employed to achieve the plasma-assisted N₂ fixation, and the coupled ion trap mass spectrometer (IT-MS) was used to detect positively charged product ions. In the model case, under APCI conditions, unusual product ions, [M + 16]⁺ and [M + 14]⁺, were observed. Based on the high resolution MS data and tandem mass spectrometric information, [M + 16]⁺ was confirmed to be protonated p-toluidine and [M + 14]⁺ was confirmed to be p-methylphenylnitrenium ion. According to the experimental results of the isotopic labelling and substituent effect, one feasible mechanism is proposed as follows. Firstly, N₂ is activated by plasma caused via the corona discharge and then electrophilically attacks toluene, yielding the key intermediate, p-methylphenylnitrenium; secondly, the intermediate undergoes double-hydrogen transfer reaction to give rise to the final product ion, protonated p-toluidine. This study may provide a novel idea to explore new and green method for the synthesis of anilines.