Convenient synthesis of cyclic carbonates from CO_2 and epoxides by simple secondary and primary ammonium iodides as metal-free catalysts under mild conditions and its application to synthesis of polymer bearing cyclic carbonate moiety

摘要

Hydroiodides of secondary and primary amines effectively catalyzed the reaction of carbon dioxide and epoxides under mild conditions such as ordinary pressure and ambient temperature, to obtain the corresponding five-membered cyclic carbonates in moderate to high yields. Detailed investigation showed that the catalytic activity was highly affected by the counter anions of the ammonium salts; the iodides catalyzed efficiently the carbonate-forming reactions, whereas the bromide and chloride counterparts exhibited almost no catalysis. We also revealed that two important factors on the amine moieties that affected the catalytic reactions. First, the catalytic activity increased with increasing bulkiness of the substituents on the ammonium nitrogen atoms. Second, the catalysis became more efficient as the parent amines become more basic. Dicyclohexylammonium iodide was the best catalyst among the ammonium salts investigated in this study. As an application of this reaction system, we synthesized homo- and copolymers bearing epoxide pendant groups as substrates, which were converted with high efficiency into the corresponding homo- and copolymers bearing cyclic carbonate pendant groups under 1 atm at 45 °C. All polymers were easily purified simply by precipitation in water, and were isolated in high yields (>95%).