Phosphonium-based ionic liquids: Economic and efficient catalysts for the solvent-free cycloaddition of CO2 to epoxidized soybean vegetable oil to obtain potential bio-based polymers precursors

Abstract

A series of phosphonium-based ionic liquids have been prepared in one step in a simple way from inexpensive feedstocks. The prepared ionic liquids have been successfully tested as catalysts in the solvent-free cycloaddition reaction of CO2 to an epoxidized soybean oil to obtain carbonated soybean oil that can be potentially employed as bio-monomer in the synthesis for bio-based polymers. The catalytic performance of these ionic liquids was compared to the widely used and benchmark catalyst in CO2 cycloaddition to epoxides reaction, namely tetrabutylammonium bromide at different reaction conditions. The influence of some reaction parameters such as temperature, CO2 pressure, reaction time and catalyst amount was studied. It has been found that the solubility of the prepared ionic liquids in the reaction media (epoxidized soybean oil) is a key factor that limits the catalytic performance of some of the synthesized ionic liquids. All prepared ionic liquids have shown higher thermal stability that the benchmark catalyst and three of them have shown superior catalytic performance. The best results in terms of conversion and selectivity have been obtained with dodecyltriphenylphosphonium bromide (5) achieving almost full conversion (99.8%) and excellent selectivity (84.0%) after 5 h reaction at 160 ºC and 40 bar of CO2. Outstanding results compared to those reported in the literature with similar catalysts in the solvent-free CO2 cycloaddtion to an epoxidized soybean oil to obtain the corresponding carbonated oil have been achieved. Considering the facile synthesis of catalyst 5, the large availability and non-expensive of the feedstocks and its catalytic performance it can be considered a valuable and green alternative for CO2 fixation to epoxidized vegetable oil.