Bifunctional catalysis by acetic acid in the urethane formation from cyclocarbonates and amines: quantum chemical and kinetic study

摘要

The mechanism of bifunctional catalysis by acetic acid in the addition reaction of amines with cyclocarbonates was studied by the DFT (PBE/TZ2P) method. Several one-step and multistep reaction pathways were found. The barrier for the transformation through the most favorable pathway in the presence of acetic acid was shown to substantially decrease (to similar to 12 kcal mol(-1)) compared to the non-catalytic reaction (similar to 33 kcal mol(-1)) and the reaction involving the second amine molecule as the catalyst (similar to 22 kcal mol(-1)). The kinetics of the model reaction of ethylene carbonate with butylamine in dioxane was experimentally studied, and it was found that the effective activation energy decreases to 5.3 and 1.1 kcal mol(-1) for the channels involving one and two amine molecules, respectively, compared to the reaction in the absence of acetic acid (14.0 and 3.7 kcal mol(-1)).