Computational study of the unimolecular and bimolecular decomposition mechanisms of propylamine

Abstract

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: H 2 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 H 2 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 nH 3 (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. Propylamine is of significant importance in chemistry, as it constitutes a central structure block for aliphatic amines 1. It is widely utilized as a solvent in organic synthesis, and as a finishing agent for drugs, rubber, fiber, paints, pesticides, textile and resin 2,3 , and in the generation of fungicides 4-6. Furthermore, it may very well be used as a petroleum additive and preservative. The disintegration of protonated of propylamine has attracted a noteworthy arrangement of fascination in the previous decade 7-10. This is mainly due to the way that the proton affinity and the structural difference in propylamine through protonation influences the separation items through the arrangement of protonated amines, methane, propene and hydrogen gas 11,12. Additionally, this reaction prompts the generation of various poisonous synthetic substances such as, alkyl cyanide, propylene, ethylene, nitrogen and hydrogen gases 13,14. Protonation (B + H + → BH +) and deprotonation (dehydrogenation) (HA − H + → A −) reactions assume a significant role in natural science and organic chemistry, where A and B are the acidic and the basic centers, respectively. They are considered as the first step in several fundamental chemical mechanisms elucidated in the cited reference 15. The ability of an atom or molecule in the gas phase to accept or to lose a proton can be described by calculating the proton affinity (PA), deprotonation (dehydrogenation) enthalpy, and molecular gasphase basicity, which offer a profound understanding of the connections between the reactivity of the organic molecules, their molecular structures, and molecular stability 16. The negative of the enthalpy change related to the gas-phase protonation reaction is referred to as proton affinity, while dehydrogenation energy is defined as the en...

Mechanistic Investigation of the Pyrolysis of Brown Grease

“…e relative energies of all stationary points in the vacuum were corrected with zero-point vibrational energies. For all proposed mechanisms, the transition states were analysed using the intrinsic reaction coordinate (IRC) [33][34][35][36][37][38][39], at B3LYP/6-31G(d) and uB3LYP/6-31G(d) levels of theory for nonradical and radical pathways, respectively, to affirm the linkage between the reactant and each of the required intermediate or product. Structures obtained from IRC were optimized to identify the minima to which each transition state is connected.…”

Benchmark calculations of proton affinity and gas‐phase basicity using multilevel (G4 and G3B3), B3LYP and MP2 computational methods of para‐substituted benzaldehyde compounds

“…10,11,19,20 The composite chemical models and the Gaussian methods such as G1-G4, 21,22 G3//B3LYP (or G3B3), 23,24 CBS-Q, CBS-4, and CBS-QB3 are recognized to provide an accurateness of $0.5-1 kcal/mol or less in comparison with the experimental results. [25][26][27][28] These methods are recognized as respectable methods to correctly calculate thermodynamic properties. The G3B3 (or G3// B3LYP) method is a modified of G3 theory in which structures and zero-point vibrational energies were computed at the B3LYP/6-31G (d) level of theory.…”

“…The B3LYP was compared up to ∼1–2 kcal/mol compared with the experimental values 10,11,19,20 . The composite chemical models and the Gaussian methods such as G1–G4, 21,22 G3//B3LYP (or G3B3), 23,24 CBS‐Q, CBS‐4, and CBS‐QB3 are recognized to provide an accurateness of ~0.5–1 kcal/mol or less in comparison with the experimental results 25–28 . These methods are recognized as respectable methods to correctly calculate thermodynamic properties.…”

Computational Insights in DNA Methylation: Catalytic and Mechanistic Elucidations

“…On one side, it is well recognized that the occurrence of 5mC is mutagenic and can cause base mispairing G-T by the deamination of 5mC to thymine [5]. The deamination reactions of nucleic acid bases and related compounds have been extensively studied, the results of which are of great value in proposing the mechanisms investigated in this work [6][7][8][9][10][11][12][13]. On the other side, however, 3mC lesion affects the stability of single-strand (ss) and double-strand (ds) DNA [3].…”