Oxidation of catechol and L-ascorbic acid by [RuIII(tpy)(pic)(OH)]+ (tpy=2,2′6′2-terpyridine; pic- = picolinate):: Kinetic and mechanistic studies

Kinetics of oxidation of catechol (H(2)cat) to benzoquinone (BQ) and, ascorbate (HA(-)) to dehydroascorbic acid (A) by [Ru-III(tpy)-(pic)(OH)](+) (1) (tpy = 2,2'6',2-terpyridine; pic(-) = picolinate) have been studied as function of [H,cat] (or [HA-]), ionic strength (0.01 - 0.25 M), temperature (10-30 degrees C) at a constant pH = 3.2, using stopped-flow and rapid-scan diode array spetrophotometric techniques. The rate of reaction of 1 with HA- was found to be very fast as compared to that of with H(2)cat. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism. Analysis of spectral and kinetic data revealed that the reaction of 1 with catechol proceeds by a straightforward outer-sphere electron transfer pathway, whereas, reduction of 1 with HA(-) involves ion-pair formation. (C) 2006 Elsevier B.V. All rights reserved.