Tuning catalyst solubility in CO2 by changing molar volume

摘要

Poor-solvating property of supercritical carbon dioxide (scCO2) has been a great challenge, which limits the use of CO2 as a common “green” solvent. The present report describes that by increasing molar volume (v) and lowering the melting temperature, which lowers cohesive energy density or solubility parameter (δ), it is possible to increase the solubility of metal-based catalysts in scCO2 without using costly fluorinated or tailor-made CO2-philic modifications. We have studied various chlorodistannoxanes (1) and Cu–β-diketonates (2) to support our views. The study of bio-diesel production and transesterification of hindered esters using 1 in scCO2 shows a 2–8-folds rate enhancement coupled with an easier catalyst and product separation than that in organic solvents. The methodology, which works at least within the range of Van der Waals sphere of interactions, can be useful to solubilizing the molecules in scCO2 and carries great opportunity in catalysis as well as in separation science.