Cycloaddition of Oxirane Group with Carbon Dioxide in the Supercritical Homogeneous State

Cycloaddition of an oxirane group of 2-methyloxirane or 2,2-dimethyloxirane with carbon dioxide was carried out in both supercritical homogeneous and vapor−liquid coexisting regions to produce a cyclic carbonate compound of 4-methyl-1,3-dioxolan-2-one or 4,4-dimethyl-1,3-dioxolan-2-one. The yield of the cyclic carbonate exceeded 95%, when the reaction proceeded in the supercritical uniform condition. On the other hand, the yield was less than 5%, when the reaction occurred in the two-phase region. While almost all kinds of alkali metal halides exhibited the high catalytic activity in a polar liquid solvent, limited numbers of halides were found to have much activity in supercritical carbon dioxide. This might be due to differences in solvent properties such as polarity and dissolving power between the supercritical and liquid solvents. The selective separation of cyclic carbonate from the supercritical mixture of reactants and products was investigated by manipulating the temperature and pressure. When decreasing the temperature and pressure of the effluent from the reactor below the critical temperature and pressure of carbon dioxide, a condensate of cyclic carbonate with a purity of more than 99% was obtained from the outlet stream.