The reduction of Fe(CN) 5 L 2− (L = pyridine, isonicotinamide, 4,4 -bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1-7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H 2 A(k 0 ), HA − (k 1 ), and A 2− (k 2 ), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka 1 and Ka 2 , the rate constants are k 0 = 1.8, 7.0, and 4.4 M −1 s −1 ; k 1 = 2.4 × 10 3 , 5.8 × 10 3 , and 5.3 × 10 3 M −1 s −1 ; k 2 = 6.5 × 10 8 , 8.8 × 10 8 , and 7.9 × 10 8 M −1 s −1 for L = py, isn, and bpy, respectively, at µ = 0.

The nitrile ligands undergo hydrolysis to amides under mild conditions when Ru(NH3)5NCR 2+ (R = 4-py, 4-pyCH3 + and CH=CHCN) complexes are oxidized to Ru(III). The rate of hydrolysis of Ru(NH3)5NCpy 3+ increases with the increase in acid concentration as a result of the protonation of the pyridyl nitrogen. The kinetic results yield the rate constant of the hydrolysis for Ru(NH 3)5NCpyH 4+ complex as 0.12 s -1 at m = 1.0 M HCl/LiCl, greater than that of a deprotonated species by nearly two orders of magnitude. The enormous increase in rate for the protonated complex arises mainly from the increase in electron withdrawing power due to protonation which will decrease the electron density on the nitrile carbon and make it easier for the nucleophilic attack of the water molecule.