Divalent/Monovalent Selectivities and Secondary Interactions of Multibasic Acids on Anion Exchange Resins

Abstract

The ion exchange equilibria of Br^– on three strongly basic anion exchange resins of different exchange capacities and different cross-linking degrees by five alkanoates (MC_<i>m</i>), a phosphate, and eight alkanedioates (DC_<i>n</i>; <i>m</i>,<i>n</i> = number of carbon atoms) were analyzed, and the selectivity coefficients for their monoanion and dianion, <i>K</i>₁₁ and <i>K</i>₂₁ were evaluated as a function of percent exchange (%E). The decrease in the <i>K</i>₁₁ values of MC_<i>m</i> with an increase in %E was attributed to the interference with hydration of MC_<i>m</i> in the resin phase, while the increase in the <i>K</i>₁₁ values of DC_<i>n</i> to the intermolecular hydrogen bonding between exchanged acidic anions. The log <i>K</i>₂₁ values of DC_<i>n</i> at %<i>E</i> = 0 plotted against <i>n</i> showed the minimum rather than the maximum as described previously. The reason has been discussed in terms of the hydrophobic interaction of DC_<i>n</i> with the polymer matrix, intramolecular hydrogen bonding, and the charge density