Computational Study of the Reaction Mechanism for the Formation of 4,5-Diaminophthalonitrile from 4,5-Dibromo-1,2-Diaminobenzene and Copper Cyanide

Abstract

This study investigates the mechanism of the reaction between 4,5-dibromo-1,2-diaminobenzene and copper cyanide using Density Functional Theory (DFT) calculations. The kinetics and the thermodynamic properties of the reaction were analyzed, revealing two major steps with activated complexes AC1 and AC2. Scheme 3 accurately depicts the reaction pathway. A triangular Cu-C=N moiety was found in the calculated transition states (TS), AC1 and AC2. The thermodynamic parameters for the first step show ΔG = -606.8 kJ mol^-1 , ΔH = -610.7 kJ mol^-1 and ΔS = -0.0132 kJ mol^-1K^-1 while for the second step ΔG = -600.1 kJ mol^-1, ΔH = -603.6 kJ mol^-1, and ΔS = -0.0117 kJ mol^-1K^-1 were obtained. The activation energies (E_a and E_c) for steps 1 and 2 are 189.0 kJ mol^-1 and 210.6 kJ mol^-1, respectively. The positive values of  and confirm the presence of energy barriers in both steps. These findings provide critical insights into the energetics and mechanism of the DDB reaction with copper cyanide, which is very crucial in understanding the strategy for the development of efficient synthetic procedures for the phthalonitrile.