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

Kinetics of oxidation of catechol (H₂cat) 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 H₂cat] (or HA⁻]), ionic strength (0.01 − 0.25 M), temperature (10–30 °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 H₂cat. 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.