Mechanism of the hydrodenitrogenation of neopentylamine and adamantylamine on sulfided NiMo/Al2O3

Neopentanethiol, 1-adamantanethiol, and 2-adamantanethiol were primary products and neopentane and adamantane were secondary products in the hydrodenitrogenation of neopentylamine, 1-adamantylamine, and 2-adamantylamine, respectively, over sulfided NiMo/Al2O3. Dialkylamines and dialkylimines were formed as primary products in the reactions of 2-adamantylamine and neopentylamine as well. None of the three amines can react by ammonia elimination and a classic SN2 substitution of the NH2 group by H2S is not possible for the adamantylamines either. The formation of di(2-adamantyl)imine and di(neopentyl)imine indicates that dehydrogenation and hydrogenation reactions occur and that imine or iminium-cation intermediates play an important role. NH2-SH substitution takes place by dehydrogenation of the amine to an imine or iminium cation, which adds H2S and eliminates NH3. The secondary character of adamantane and neopentane demonstrates that hydrogenolysis of the aliphatic C–N bond does not take place over sulfided NiMo/Al2O3 below 340 °C. Even though 1-adamantylamine can neither react by classic SN2, E1, and E2 reactions, nor via an imine or iminium cation, it formed 1-adamanethiol at 300 °C. This reaction might take place by an SN1 reaction or by adsorption of the amine at a surface vacancy, followed by a shift of the adamantyl group to a neighboring sulfur atom.