Direct and Efficient Dehydrogenation of Tetrahydroquinolines and Primary Amines Using Corona Discharge Generated on Ambient Hydrophobic Paper Substrate.

The exposure of an aqueous-based liquid drop containing amines and graphite particles to plasma generated by a corona discharge results in heterogeneous aerobic dehydrogenation reactions. This green oxidation reaction occurring in ambient air afforded the corresponding quinolines and nitriles from tetrahydroquinolines and primary amines, respectively, at >96% yields in less than 2 min of reaction time. The accelerated dehydrogenation reactions occurred on the surface of a low energy hydrophobic paper, which served both as container for holding the reacting liquid drop and as a medium for achieving paper spray ionization of reaction products for subsequent characterization by ambient mass spectrometry. Control experiments indicate superoxide anions (O2(•-)) are the main reactive species; the presence of graphite particles introduced heterogeneous surface effects, and enabled the efficient sampling of the plasma into the grounded analyte droplet solution. Graphical Abstract ᅟ.