Mechanism of the C-N-bond breaking in the hydrodenitrogenation of methylcyclohexylamine over sulfided NiMo/gamma-Al2O3

The hydrodenitrogenation (HDN) of methylcyclohexylamine was studied over su lfided NiMo/gamma -Al2O3. 2-Methyl-cyclohexylamine (MCHA) is an intermediat e in the HDN of toluidine that can be detected in addition to the main prod ucts, methylcyclohexene (MCHE) and methylcyclohexane (MCH), when a high qua ntity of cyclohexene (CHE) was added to a-toluidine during HDN. The selecti vity of MCH in the HDN of MCHA was about 20% at zero conversion. The detect ion of 2-methylcyclohexanethiol (MCHT) in the HDN of MCHA explains why MCH is observed as a quasi primary product in the HDN of o-toluidine. MCH is fo rmed via nucleophilic substitution of the amine group of MCHA, giving MCHT, followed by C-S bond hydrogenolysis. A kinetic investigation at different H2S partial pressures showed that H2S increases the rate of nucleophilic su bstitution, but leaves the rate of the beta -Hofmann elimination of ammonia from MCHA unchanged. (C) 2000 Elsevier Science B.V. All rights reserved.