Kinetics and Mechanism of the One-Electron Reduction of Iodine by [Ru(II)(NH(3))(5)isn](2+) in Aqueous Solution.
Iodine oxidizes [Ru(II)(NH(3))(5)isn](2+) in mildly acidic (HClO(4)) aqueous solution at 25 degrees C according to the reaction I(2) + 2[Ru(II)(NH(3))(5)isn](2+) --> 2I(-) + 2[Ru(III)(NH(3))(5)isn](3+). The rate law is -d[Ru(II)]/dt = {2k(1)[I(2)] + 2k(2)[I(3)(-)]}[Ru(II)] with k(1) = 4.3 x 10(3) M(-)(1) s(-)(1) and k(2) = 80 M(-)(1) s(-)(1) at &mgr; = 0.10 M (NaClO(4)). An outer-sphere electron-transfer mechanism is proposed for both terms of the rate law, with the k(1) term corresponding to the formation of I(2)(-) and k(2) corresponding to the formation of I(2)(-) plus I(-). Subsequent reduction of I(2)(-) by Ru(II) to form I(-) is expected to be fast. A value of 2.7 for log(k(22)) (the I(2)/I(2)(-) self-exchange rate constant) is derived from the Marcus cross relationship.
Sun
Jiafei
J
Department of Chemistry, Auburn University, Auburn, Alabama 36849.
Stanbury
David M.
DM