A KINETIC-STUDY OF ELECTRON-TRANSFER FROM L-ASCORBIC-ACID TO SODIUM PERBORATE AND POTASSIUM PEROXY DISULFATE IN AQUEOUS ACID AND MICELLAR MEDIA

Kinetics of oxidation of L-ascorbic acid (H(2)A) by sodium perborate ( SPB) and peroxy disulphate (PDS) have been investigated in aqueous aci d and micellar media. Reaction kinetics indicated first-order dependen ce on both [oxidant] and [H(2)A]. Increase in ionic strength (mu) incr eased reaction rate only in H2SO(4) media. Rate of SPB oxidation of H( 2)A has been accelerated by acidity in HNO3 and HCl media while a decr easing trend is observed in HClO4 and H2SO4 media. The results are int erpreted by various theories of acidity functions. Reaction rate is en hanced by the addition of added [H2O2] indicating a H2O2 coordinated b oron species to be active in the present system. In the absence of mic elle, increase in [acid] altered the PDS-H(2)A reaction rate marginall y (a very small positive effect with HClO4 and negative effect with H2 SO4) Most plausible mechanisms have been proposed on the basis of expe rimental results. Activation parameters evaluated for specific kinetic constants are in accord with outer sphere electron transfer mechanism . In SPB-H(2)A system, addition of anionic micelle (Sodium lauryl sulf ate) increased the rate, stabilizing the cationic species in the trans ition state in ail the acid media. Although rate of PDS oxidation of H (2)A was catalyzed by TX and inhibited by SDS at critical micellar con centration (CMC) increase in [acid] (both HClO4 and H2SO4) beyond 9.6 x 10(-4) M decreased the rate of oxidation. This trend was explained d ue to the repulsive interaction of coanion, HA(-), and negatively char ged micellar species. (C) 1996 John Wiley & Sons, inc.