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A kinetic study of electron transfer from L‐Ascorbic acid to sodium perborate and potassium peroxy disulphate in aqueous acid and micellar media
Author(s) -
Rajanna K. C.,
Reddy K. Narsi,
Kumar U. Umesh,
Sai Prakash P. K.
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:3<153::aid-kin1>3.0.co;2-u
Subject(s) - chemistry , sodium perborate , ascorbic acid , aqueous solution , potassium , aqueous medium , electron transfer , sodium , kinetic energy , inorganic chemistry , hydrogen peroxide , nuclear chemistry , organic chemistry , food science , physics , quantum mechanics
Kinetics of oxidation of L‐ascorbic acid (H 2 A) by sodium perborate (SPB) and peroxy disulphate (PDS) have been investigated in aqueous acid and micellar media. Reaction kinetics indicated first‐order dependence on both |oxidant| and |H 2 A|. Increase in ionic strength (μ) increased reaction rate only in H 2 SO 4 media. Rate of SPB oxidation of H 2 A has been accelerated by acidity in HNO 3 and HCl media while a decreasing trend is observed in HClO 4 and H 2 SO 4 media. The results are interpreted by various theories of acidity functions. Reaction rate is enhanced by the addition of added |H 2 O 2 | indicating a H 2 O 2 coordinated boron species to be active in the present system. In the absence of micelle, increase in |acid| altered the PDS(SINGLEBOND)H 2 A reaction rate marginally (a very small positive effect with HClO 4 and negative effect with H 2 SO 4 ). Most plausible mechanisms have been proposed on the basis of experimental results. Activation parameters evaluated for specific kinetic constants are in accord with outer sphere electron transfer mechanism. In SPB(SINGLEBOND)H 2 A system, addition of anionic micelle (Sodium lauryl sulfate) increased the rate, stabilizing the cationic species in the transition state in all the acid media. Although rate of PDS oxidation of H 2 A was catalyzed by TX and inhibited by SDS at critical micellar concentration (CMC) increase in |acid| (both HClO 4 and H 2 SO 4 ) beyond 9.6 × 10 −4 M decreased the rate of oxidation. This trend was explained due to the repulsive interaction of coanion, HA − , and negatively charged micellar species. © 1996 John Wiley & Sons, Inc.