Solvent Extraction of Phthalate Isomer Dianions by the Use of Dicationic Anion-Exchange Extractants

Abstract

The extraction of phthalate isomer dianions (phthalate, isophthalate and terephthalate) was studied by the use of dicationic anion-exchange extractants, polymethylenebis(trioctylphosphonium)s (abbreviated as CBP). Extraction equilibrium studies confirmed that the extraction reaction of phthalate isomers under high pH condition (pH>11) occurs via the formation of a 1:1 ion-pair complex between C_nBP and the phthalate isomer. The extraction ability of dicationic extractants was greatly superior to that of conventional monocationic extractants. Further, the extraction ability of dicationic extractants was dependent on the length of the bridging methylene-chain between two phosphonium cationic centers within the extractants. In the extractions of phthalate, isophthalate and terephthalate, the most favorable extractants were C₄BP, GBP and C₈BP, respectively. Thus, since the distance between the two anionic centers of phthalate isomer is longer, the bridge-chain length of the most preferable extractant is longer.