TITLE:
Spectral Evidence for the One-Step Three-Electron Oxidation of Phenylsufinylacetic Acid and Oxalic Acid by Cr(VI)
AUTHORS:
Perumal Subramaniam, Natesan Thamil Selvi
KEYWORDS:
Phenylsulfinylacetic Acid; Oxalic Acid; Co-Oxidation; Nucleophilic Attack of Sulfur; Three-Electron Transfer; Substituent Effect
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.4 No.10A,
September
26,
2013
ABSTRACT:
The co-oxidation of a
mixture of phenylsulfinylacetic acid (PSAA) and oxalic acid (OxH2)
by Cr(VI) in 20% acetonitrile-80% water (v/v) medium follows third order
kinetics, first order, each with respect to PSAA, OxH2 and Cr(VI). The reaction
involves nucleophilic attack of sulfur atom of PSAA on chromium of the
oxidizing species, Cr(VI)-OxH2 to
form a ternary complex, Cr(VI)-OxH2-PSAA followed by a one-step
three-electron reduction of Cr(VI) to Cr(III) and simultaneous oxidation of
both the substrates. The reaction is catalysed by Mn2+ ion while
retarded by Al3+ ion. Electron releasing substituents in the
meta- and para-positions of the phenyl ring of PSAA enhance the rate of
co-oxidation while electron withdrawing substituents retards the
reaction. The Hammett plots at different temperatures exhibit excellent
correlation with negative ρ values.
The reaction series obey isokinetic relationship and the observed isokinetic
temperature is lying below the experimental range of temperature.