Mechanism of CN bond breaking in hydrodenitrogenation

CN bond rupture is the final step in the hydrodenitrogenation of nitrogen-containing molecules and occurs by substitution of the alkylamine by H2S to form an alkanethiol and NH3. To study the mechanism of the CN bond breaking, we investigated the reactions of the chiral 2-(S)-butylamine and of N,N-dihexylmethylamine. The amine-to-thiol substitution occurred not through a classic organic substitution reaction, but rather through (de)hydrogenation steps via an imine or through redox and (de)protonation steps, in which an alkyliminium cation acts as an intermediate. For alkylamines and dialkylamines, the reaction may well occur via imine intermediates, but for trialkylamines, the intermediate can only be an iminium ion.