Green chemistry of polyurethanes: The catalytic n-butylaminolysis of ethylene carbonate as a model chain-growth reaction in the formation of nonisocyanate polyurethanes

The kinetic regularities and the mechanism of the catalytic action of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, which is the most active of the known catalysts for the formation of hydroxyurethanes from cyclocarbonates and amines, were studied using the example of the n-butylaminolysis of ethylene carbonate. In contrast with the noncatalytic reaction, which proceeds via two parallel pathways that involve one and two molecules of amine, the catalytic reaction follows a single pathway: the second molecule of amine is replaced by a molecule of the catalyst that accelerates the process in accordance with the mechanism of bifunctional catalysis. Different reaction pathways were studied by quantum chemical calculations based on the density functional method. It was shown that the high activity of 1,5,7-triazabicyclo[4.4.0]dec-5-ene results from the formation of a planar cation-like form of the catalyst. Moreover, the low-energy transition between the cation and the initial 1,5,7-triazabicyclo[4.4.0]dec-5-ene enables the catalyst to simultaneously be a good donor and acceptor of protons. This study presents a new way for finding among bifunctional organic compounds the catalysts that are even more active in the reaction of cyclocarbonates with amines.