Abstract
Polarographic reduction currents of pyridinecarboxaldehydes and their N-methyl-derivatives increase (with increasing pH) at pH>7 in the shapes of a dissociation curve. This increase occurs in a pH-range several pH-units lower than that of the p K for the dissociation of the corresponding geminal diol. This behavior is interpreted by assuming that the rate of dissociation yielding the geminal diol anion is the rate-determining step in the electrode process followed by fast elimination of a hydroxide ion. By comparing the shapes of the i 1-pH plots it was concluded that whereas for N-methylpyridiniumcarboxaldehydes the protolytic dissociation (5b) predominates, for 4-pyridinecarboxaldehyde, the predominating path is the hydrolytic dissociation (5a). It has been demonstrated that in these cases the conjugate acid is electroinactive and the conjugate base is effectively reduced (after a rapid transformation into an electroreducible species). Such a mechanism is indicated by the shift of the polarographic dissociation curve to pH-values lower than the true p K.
Published Version
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