DISSOCIATION CONSTANTS OF 2-AMINO-2-DEOXY-D-GLUCOPYRANOSE

Experiments have been performed to demonstrate that the two anomers of D-glucosamine have different dissociation constants for the amino-group. These dissociation constants have been measured by means of the change in pH that occurs when each of the pure anomers is dissolved in half an equivalent of acid or alkali. Extrapolation of the curves so obtained to zero time permits the estimation of the dissociation constants. Experiments performed over a range of temperatures have yielded values for ΔG, ΔH, and ΔS. An equation has been derived which permits the calculation of mutarotation constants from the dissociation constants and the pH at equilibrium. It is suggested that the dissociation constants of the two anomers differ either because of differences in solvation or, less probably, because of differences in the proximity of neighbouring hydroxy-groups.