New Highly CO2-Philic Diglycolic Acid Esters: Synthesis and Solubility in Supercritical Carbon Dioxide

A series of diglycolic acid esters, potent CO2-philic chelating agents, were designed and synthesized. The solubilities of these compounds in supercritical CO2 were determined at temperatures from (313 to 333) K and pressures from (8.6 to 20.4) MPa. All of the synthesized esters showed good to high solubility (as high as 1.6.10(-2) mol.mL(-1) for compound 1 at 9.3 MPa and 313 K) in supercritical CO2 at easily accessible temperatures and pressures. To confirm the tested solubility, two density-based correlations proposed by Bartle and Chrastil were investigated for the seven glycolic acid esters. The results showed good self-consistency of the data calculated by the Bartle semiempirical equation and differed from the measured values by between (4 and 37) %. Better agreement with experimental solubility data is obtained with the Chrastil model, and values of AARD lower than 11 % were observed. Solubility data were also used to estimate the partial molar volume (V) over bar (2) for each diglycolic acid ester in the supercritical phase using the theory developed by Kumar and Johnston.