A Comparison of Catalytic Activity of Ammonium and Phosphonium Salts in Carboxylation of Epoxides without Lewis Acids

A comparative analysis was performed to evaluate the catalytic efficiency of various organocatalysts for the carboxylation of epoxides based on ammonium and phosphonium salts. The results show that for low molecular weight onium salts, the efficiency of epoxide carboxylation depends on both the catalyst structure and its solubility in the reaction medium. The highest efficiency was achieved with tetrabutyl-substituted onium iodides and bromides. The addition of 20 mol % water together with the onium salt significantly accelerates the reaction with epoxides and results in quantitative yields of mono- and disubstituted cyclic carbonates. A polystyrene-based catalyst modified with an immobilized tributylphosphonium group (4 mol %) combined with 1 eq. of water produces a quantitative yield of butylene carbonate and can be reused without loss of catalytic activity (tested over 10 cycles), making it promising for practical applications.