KINETICS AND MECHANISM OF THE OXIDATION OF D-GALACTOSE BY COPPER(II) IN ACIDIC MEDIUM

The oxidation of D-galactose by Cu-II has been studied in acetate buffers within the pH range 4-4.75 at 110 degrees C. The observed pseudo-first-order rate constant is given by k(obs) = {k(a) + k(b)/[H+] + k(c)/[H+](2)}[gal]/{1 + (k(d) + k(e)/[H+])[gal]} where k(a) = 2.77 x 10(-3) M(-1) s(-1), k(b) = (1.22 +/- 0.11) x 10(-7) S-1, k(c) = (1.12 +/- 0.16) x 10(-12) M s(-1), k(d) = 2.08 M(-1), k(e) = (2.75 +/- 0.33) x 10(-5). This rate law corresponds to the formation of galactonic acid and Cu-I when a 10 fold or higher excess of D-galactose over Cu-II is employed. The results are discussed in terms of a possible mechanism of oxidation of the enodiol of galactose by CuOAc+, present in solution.