Reactivity comparison of five- and six-membered cyclic carbonates with amines: Basic evaluation for synthesis of poly(hydroxyurethane)

The reaction of six- and five-membered cyclic carbonates, 5-(2-propenyl)-1,3-dioxan-2-one (1) and 4-(3-butenyl)-1,3-dioxolan-2-one (2) with hexylamine and benzylamine was carried out in N,N-dimethylacetamide at 30, 50, and 70 °C. The six-membered cyclic carbonate 1 proceeded quantitatively with hexylamine at 30 °C for 24 h, while the five-membered cyclic carbonate 2 converted in 34%. The reaction rate constants at 50 °C are evaluated as follows; 1.42 L/mol · h (1 with hexylamine) > 0.29 L/mol · h (1 with benzylamine) > 0.04 L/mol · h (2 with hexylamine) > 0.01 L/mol · h (2 with benzylamine). The activation energies in the reactions of 1 and 2 with hexylamine were estimated to be 10.1 and 24.6 kJ/mol, respectively. The ring-strain energy was calculated by the semi-empirical method using the PM3 Hamiltonian. The ring-strain energy of the six-membered cyclic carbonate was 2.86 kcal/mol larger than that of five-membered one.