KINETICS AND MECHANISMS OF REDUCTION OF CHROMIUM(6) BY SUBSTITUTION-INERT IRON(2) COMPLEXES IN ACIDIC AQUEOUS SOLUTION

The kinetics of the reaction of chromium(VI) with Fe(CN)64- Fe(bip)(CN)42- (bip = 2,2ʹ-bipyridine), Fe(bip)2(CN)2, and Fe(bip)32+ have been examined over wide ranges of initial concentrations at 25.0° in per-chlorate solutions of 0.50 M ionic strength. Each reaction follows the rate equation, – d[HCrO4]/dt =K2[HCrO4−] • [Fe(II)], where k2 is a complex function of [H+]. A major product of the reactions of the cyanoiron(II) complexes is in each case apparently a Cr(III)-Fe(III) binuclear complex. A comparison of these results with those of previous studies on related systems indicates that the form of the rate equation can be correlated quite well with the relative substitution-inertness of one-equivalent reducing agents. © 1969, American Chemical Society. All rights reserved.