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 N(2) gas as the nitrogen source. The corona discharge device within an atmospheric pressure chemical ionization source was employed to achieve the plasma-assisted N(2) 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, N(2) 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.