Methoxide Complexes of Metal Ions in Methanol
The formation of methoxide complexes was studied by measuring the pH in titrations, with methylate, of the chlorides and methylates of metals, in absolute methanol. The pH determinations were carried out with Pt/H2 or Pd/H2 electrodes, which were found to respond rapidly, reproducibly and strictly proportional to the logarithms of the concentrations of solvated protons. The problem of changing activity coefficients and ion-pair formation were avoided by the use of high concentrations (1 F) of a supporting electrolyte [N(CH3)4Cl or LiCl]. The latter effect may be serious because the dielectric constant of the solvent is about one third that of water. Because of the high concentration of supporting electrolyte the cations (H+ and cationic methoxide complexes) will form ion pairs predominantly with Cl-, with concentrations proportional to that of the free cations. Similar considerations apply to the anions (OR- and anionic methoxide complexes). Simple mass-action expressions can therefore be used, provided that symbols like M∂ + are understood to include solvatedi ∂ +stood to nclude and on-pair species that contain M. The kinds of species involved here are, of course, not known.
KeywordsTitration Curve Absolute Methanol Buffer Region Solvate Proton Free Cation
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