Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C1NHC6 and C1N(C6)2 was studied over sulfided NiMo/γ-Al2O3 at 280 °C and 3 MPa. C1NHC6 reacted by disproportionation to C1N(C6)2 as well as C6N(C1)2 and by substitution by H2S to methylamine and hexanethiol as well as hexylamine and methanethiol. C1N(C6)2 reacted by substitution with H2S to C1NHC6 and C6NHC6 and methane- and hexanethiol. The probability of breaking the C1N bond was only slightly smaller than of breaking the C6N bond in C1N(C6)2. In the reaction of an equimolar mixture of C5NHC5 and C1N(C6)2 both C1N(C5)2 and C6N(C5)2 were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.