Hydrogen bonding part 68. Infrared and titrametric study of the effect of fluoride ion on the dissolution of quinolinic acid (2,3-pyridinedicarboxylic acid)

Abstract

Quinolinic acid is a zwitterion in the solid state, with one acid hydrogen on nitrogen and the other in a three-center covalent OHO hydrogen bond between carboxylate groups. However, p K a values, the shape of the titration curve, and the formation of hydrogen quinolate ion with an OHO hydrogen bond on half-neutralization suggests that in aqueous solution quinolinic acid is a normal dicarboxylic acid analogous to phthalic acid. Addition of fluoride ion to saturated aqueous solutions of quinolinic acid increases the solubility, and 1.5F − are required for each diacid molecule solubilized. The products of the dissolution process are sodium hydrogen quinolate—identical to that derived from half-neutralization by sodium hydroxide—and sodium dihydrogen trifluoride. The formation of H 2F − 3, rather than HF − 2 which is observed in the dissolution of phthalic acid, is accounted for by the increased acidity and much greater solubility of quinolinic acid relative to phthalic acid. The interaction of quinolinic acid with fluoride ion is completely different than that of the zwitterionic 1-methyl-3,4-dicarboxyimidazole which we have previously reported.