HYDROGEN-BONDING PART 68 - INFRARED AND TITRAMETRIC STUDY OF THE EFFECT OF FLUORIDE-ION ON THE DISSOLUTION OF QUINOLINIC ACID (2,3-PYRIDINEDICARBOXYLIC ACID)

Quinolinic acid is a zwitterion in the solid state, with one acid hydr ogen on nitrogen and the other in a three-center covalent O-H-O hydrog en bond between carboxylate groups. However, pK(a) values, the shape o f the titration curve, and the formation of hydrogen quinolate ion wit h an O-H-O hydrogen bond on half-neutralization suggests that in aqueo us solution quinolinic acid is a normal dicarboxylic acid analogous to phthalic acid. Addition of fluoride ion to saturated aqueous solution s of quinolinic acid increases the solubility, and 1.5F(-) are require d for each diacid molecule solubilized. The products of the dissolutio n process are sodium hydrogen quinolate-identical to that derived from half-neutralization by sodium hydroxide-and sodium dihydrogen trifluo ride. The formation of H2F3- rather than HF2- which is observed in the dissolution of phthalic acid, is accounted for by the increased acidi ty and much greater solubility of quinolinic acid relative to phthalic acid. The interaction of quinolinic acid with fluoride ion is complet ely different than that of the zwitterionic 1-methyl-3,4-dicarboxyimid azole which we have previously reported. (C) 1998 Elsevier Science B.V . All rights reserved.