Ashok Kumar Singh*, Vinod Kumar Singh, Shahla Rahmani, Jaya Srivastava and Bharat Singh Department of Chemistry, University of Allahabad, Allahabad-211002, INDIA, ashokeks@rediffmail.com

(Received 15 December 2005; accepted 27 February 2006)

Abstract: The kinetics of oxidation of D-galactose (Gal) and L-sorbose (Sor) by N-bromoacetamide (NBA) in the presence of Pd(II) as catalyst and Hg(II) as co-catalyst are presented. The reactions follow identical kinetics, being first order in both substrates and Pd(II). The first order kinetics with respect to NBA at low concentrations tends to zero-order in its higher concentration range. Positive effect of [Hg(II)] and decreasing effect of [H⁺], [Cl^-] and [NHA] on the rate of oxidation of Gal and Sor were observed. A zero effect of variation of ionic strength of the medium on the rate of oxidation was observed. Utilizing the values of observed rate constants at four different temperatures, the activation parameters have been calculated for each reducing sugars. D-lyxonic acid and L-threonic acid were identified as the main reaction products in the oxidation of D-galactose and L-sorbose, respectively. The results are in accord with a mechanism in

 which the complex, in the rate determining step, decomposes into an intermediate which finally changes  into products through a series of fast steps with regeneration of effective species of the catalyst.

Key words: Mechanism, Pd(II) and Hg(II) co-catalysis, Acidic medium, Oxidation, Reducing sugars, N-bromoacetamide.

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