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4. Osmium(VIII) Catalyzed Oxidation of some sugars in
presence of alkaline potassium bromate
Sheila Srivastava* Shalini Singh, Parul Srivastava and Arti Jaiswal
Spectro-kinetic Lab, Feroze Gandhi College, Rae Bareli – 229001,
U.P., India
*Author for correspondence: E-mail:
she_ila72@yahoo.com
Abstract:
Osmium(VIII) catalyzed oxidation of some sugars (D-glucose &
D-galactose) by potassium bromate in alkaline medium is
found to occur via oxidant-catalyst complex formation in a
slow step followed by the interaction of substrate and
complex in the fast step to yield the products with
regeneration of catalyst. The reaction is carried out in the
presence of mercuric acetate as a scavenger for bromide ion.
The reaction shows zero order in substrates(D-glucose & D-galactose),
first order each in [KBrO3] and [Os(VIII)] and
positive effect with respect to [OH-]. Negligible
effect of change in Hg(OAc)2, ionic strength of
the medium and D2O has been observed. [OsO4
(H2O)2] and [HBrO3] are the
reactive species of Os(VIII)oxide and potassium bromate,
respectively. Gluconic acid and Galactonic acid have been
identified as the main oxidation products of the reaction.
Various activation parameters have been calculated and
recorded. A suitable mechanism in conformity with the
kinetic observations has been proposed and the thermodynamic
parameters computed.
Keywords
: kinetics, Os(VIII), catalysis, D-glucose, D-galactose,
KBrO3.
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