Computational study of the unimolecular and bimolecular decomposition mechanisms of propylamine

A detailed computational study of the dehydrogenation reaction of trans-propylamine (trans-PA) in the gas phase has been performed using density functional method (DFT) and CBS-QB3 calculations. Different mechanistic pathways were studied for the reaction of n-propylamine. Both thermodynamic functions and activation parameters were calculated for all investigated pathways. Most of the dehydrogenation reaction mechanisms occur in a concerted step transition state as an exothermic process. The mechanisms for pathways A and B comprise two key-steps: H₂ eliminated from PA leading to the formation of allylamine that undergoes an unimolecular dissociation in the second step of the mechanism. Among these pathways, the formation of ethyl cyanide and H₂ is the most significant one (pathway B), both kinetically and thermodynamically, with an energy barrier of 416 kJ mol^-1. The individual mechanisms for the pathways from C to N involve the dehydrogenation reaction of PA via hydrogen ion, ammonia ion and methyl cation. The formation of α-propylamine cation and NH₃ (pathway E) is the most favorable reaction with an activation barrier of 1 kJ mol^-1. This pathway has the lowest activation energy calculated of all proposed pathways.