HYDROGEN-BONDING .66. FURTHER-STUDIES OF THE FLUORIDE-ION ASSISTED DISSOLUTION OF 1-METHYL-4,5-DICARBOXYIMIDAZOLE - ABSENCE OF CATION PARTICIPATION AND STOICHIOMETRIC CONSIDERATIONS

Excess 1-methyl-4,5-dicarboxyimidazole (H2MDCI) dissolves into saturat ed solution in the presence of sodium fluoride, and precisely four F- are required for each H2MDCI solubilized. To account for the apparent removal of two acidic hydrogens from H2MDCI in the presence of undisso ciated diacid we postulated strong complexation of Na+ by MDCI2-. We n ow find that the dissolution behavior of H2MDCI in the presence of eit her cesium or tetramethylammonium fluoride is identical to that with s odium fluoride. As cesium ion should bind weakly if at all to MDCI2-, and tetramethylammonium ion should not be bound, we conclude that the cation present plays no role in the fluoride ion assisted dissolution of H2MDCI. Analysis of dissolution stoichiometry and titration data su ggests the possibility that two F- react with H2MDCI to form HMDCI- an d HF2- and that two more F- are required but do not act to abstract ac id hydrogen. (C) 1997 Elsevier Science B.V.