Chromic acid oxidation of hexitols in the presence of 2,2′-bipyridyl catalyst in aqueous micellar media: A kinetic study

✍ Scribed by Monirul Islam; Bidyut Saha; Asim K. Das

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 267 KB
• Volume: 38
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20181

✦ Synopsis

Abstract

In aqueous H~2~SO~4~ media, chromic acid oxidation of hexitols (D‐sorbitol and D‐mannitol) to their corresponding aldohexoses in presence and absence of 2,2′‐bipyridyl (bipy) have been studied under the experimental conditions, [hexitols]~T~ ≫ [Cr(VI)]~T~ and [bipy]~T~ ≫ [Cr(VI)]~T~ (subscript T stands for the total concentration). Under the conditions, both the slower uncatalyzed and faster bipy‐catalyzed paths go on simultaneously. The monomeric species of Cr(VI) has been found to be kinetically active in absence of bipy whereas in the bipy‐catalyzed path, the Cr(VI)–bipy complex has been found to be the active oxidant. Both the paths show first‐order dependence on [hexitol]~T~ and [Cr(VI) ]~T~. The uncatalyzed path shows a second‐order dependence on [H^+^]. The bipy‐catalyzed path is first order in [bipy]~T~. These rate‐dependence patterns remain the same in the presence of externally added surfactants. Sodium dodecyl sulfate (SDS), an anionic surfactant, has been found to accelerate both the uncatalyzed and bipy‐catalyzed paths while N‐cetylpyridinium chloride (CPC), a cationic surfactant, shows the rate‐retarding effect for both the uncatalyzed and bipy‐catalyzed paths. The observed micellar effects have been rationalized by considering the distribution of the reactants between the aqueous and micellar phases in terms of the proposed reaction mechanism. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 531–539, 2006