Hydrogen bonding. Part 66. Further studies of the fluoride ion assisted dissolution of 1-methyl-4,5-dicarboxyimidazole: Absence of cation participation and stoichiometric considerations

Article abstract of DOI:10.1016/S0022-2860(96)09431-8

Excess 1-methyl-4,5-dicarboxyimidazole (H₂MDCI) dissolves into saturated 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 undissociated diacid we postulated strong complexation of Na⁺ by MDCI^2-. We now find that the dissolution behavior of H₂MDCI in the presence of either cesium or tetramethylammonium fluoride is identical to that with sodium fluoride. As cesium ion should bind weakly if at all to MDCI^2-, 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 suggests the possibility that two F^- react with H₂MDCI to form HMDCI⁺ and HF₂/^- and that two more F are required but do not act to abstract acid hydrogen.