Solubilities of novel ethylene oxide diphosphate-based chelating agents in supercritical carbon dioxide

The solubilities of newly synthesized chelating agents, i.e. diethylene glycol bis (2,4,4-trimethyl-1-pentyl) dimethyl diphosphate (EG2TP), diethylene glycol bis (3,5,5-trimethyl-1-hexyl) dimethyl diphosphate (EG2TH), and diethylene glycol dioctyl dimethyl diphosphate (EG2Oct) in supercritical carbon dioxide (scCO 2 ) were determined at temperatures ranging from 313 to 333   K and pressures ranging from 9 to 17   MPa. Solubility increases in the order of EG2Oct (MW   =   518.56)   <   EG2TH (MW   =   546.61)   <   EG2TP (MW   =   518.56). Solubility parameter and connectivity index of these compounds were calculated and discussed, which indicated that branched side chains of the ligands play an important part in increasing solubility in scCO 2 . A semi empirical model proposed by Bartle was used to correlate the experimental data and AARD values were calculated to be 5.2%, 4.4%, and 3.4% for EG2TP, EG2TH, and EG2Oct, respectively. Also the quantum chemical calculation and COSMO-RS method were introduced to estimate the structure effect on the interaction with CO 2 by computing the charge density distribution on the surface of these compounds. As expected, better masking effect of the side chains result in higher solubility.