1986 Volume 2 Issue 3 Pages 293-297
The effect of organic solvents or additives was studied for the anion-exchange extraction reaction, (Q•Br)o+(X-)w_??_(Q•X)o+(Br-)w (Q+: liquid anion-exchanger; X: Cl-, I-, ClO4-; subscripts o and w denote organic and aqueous phases, respectively), with a special interest in the solvation of extracted anionic species by protic solvents or additives. The preference of extraction generally followed the order ClO4->I->Br->Cl-, whether the solvent is protic or aprotic. However, protic compounds such as phenols, alcohols, sulfonamides, carboxamides, and chloroform when used as solvent or additive showed a mitigating effect on such extraction preference. lipophilic phenols such as p-t-octylphenol (p-(1, 1, 3, 3-tetramethylbutyl)phenol) and p-nonylphenol were especially efficient in enhancing the extractability of small (and thus hydrophilic) anions. The effect of substituents on the phenol was investigated. o-Chlorination or o-bromination of p-t-octyl phenol lead to the increase of small-anion extractability. On the contrary, the o-nitration considerably lowered the ability of phenolic compound in assisting the extraction of small anions. o, o′-Dibromination and o, o′-dimethylation lead to further lowering of such ability. The mechanism of protic solvation and its importance in determining the extraction selectivity among Cl-, Br-, I-, and ClO4- were discussed.
