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 C1single bondNHsingle bondC6 and C1single bondN(C6)2 was studied over sulfided NiMo/γ-Al2O3 at 280 °C and 3 MPa. C1single bondNHsingle bondC6 reacted by disproportionation to C1single bondN(C6)2 as well as C6single bondN(C1)2 and by substitution by H2S to methylamine and hexanethiol as well as hexylamine and methanethiol. C1single bondN(C6)2 reacted by substitution with H2S to C1single bondNHsingle bondC6 and C6single bondNHsingle bondC6 and methane- and hexanethiol. The probability of breaking the C1single bondN bond was only slightly smaller than of breaking the C6single bondN bond in C1single bondN(C6)2. In the reaction of an equimolar mixture of C5single bondNHsingle bondC5 and C1single bondN(C6)2 both C1single bondN(C5)2 and C6single bondN(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.