Theoretical study of acetylation of p-methylaniline catalyzed by Ni2+ ions

Abstract

A theoretical study of acetylation of p-methylaniline catalyzed by Ni2+ ions from the analysis of intermediate of the reaction was carried out. The study of acetylation of amines is of great interest by the utility of its products of reaction and is one of the most frequently used transformations in organic synthesis as it provides an efficient and inexpensive means for protecting amino groups in a multistep synthetic process. Acetylation of amine is a nucleophilic substitution reaction. This reaction can be catalyzed by Lewis acid1 , metallic ion. The reaction and the compounds studied are shown in Figure1. + + H3C O OH O O O H3C CH3 H3C NH2 Ni 2+ H3C O NH Fig. 1: General Scheme of Acetylation In reaction mechanism, the metallic ion formed a complex with the oxygen of the acetic anhydride carbonyl, facilitating the polarization of the same and the successive addition of amine at the position to form a tetrahedral intermediate, determining step of the rate of the reaction. Experimental work2 agreed that this reaction takes place with the formation of a tetrahedral intermediate. In the present theoretical work were investigated the structure and energy of the tetrahedral intermediate of the reaction catalyzed by Ni2+ ions. Geometries of all species involved in the acetylation were made and identified. All of the geometry optimizations were performed by the method at the DFT/B3LYP level of theory and was adopted the 6-31+G* basis set. Energies were calculated using the Mechanics-UFF method. Following the same procedure it was identified the geometric parameters and energy of reaction intermediate. The calculations show 61.89 kcal/mol of energy for the tetrahedral intermediate and the energy of activation for the reaction was 16.05 kcal/mol.