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IJC-A Vol.46A(03) [March 2007] >


Title: Homogeneous catalysis of manganese(II) in the oxidation of citric acid by bromate: A novel kinetic behaviour of citric acid
Authors: Reddy, Cherkupally Sanjeeva
Issue Date: Mar-2007
Publisher: CSIR
IPC CodeInt. Cl. ⁸ B01J8/00; C07B33/00
Abstract: The kinetic and mechanistic studies on Mn(II)-catalysed oxidation of citric acid by acid bromate in presence of Hg(II) as a scavenger have been carried out under varying conditions. The reaction exhibits 1.5 order each in [bromate] and [acid], and less than unit order in [Mn(II)]. The kinetic behaviour of citric acid is novel, being 0.30 order in the lower [citric acid] range and tending to –0.25 order at higher [citric acid]. Hg(OAc)₂ and D₂O have insignificant effect on the reaction rate. Formal redox potential for the Mn(II)/Mn(III)–citric acid couple is determined as 0.32 V (vs SCE) and 0.58 V (vs NHE). These findings are accounted quantitatively by the formation of 1:1 (MnCt) and 1:2 (MnCt₂) manganese(II)-citric acid complexes of which only 1:1 (MnCt) complex is kinetically active towards the bromate oxidation. In the envisaged mechanism, acid bromate reacts with the 1:1 (MnCt) complex, whose formation is precedent to the Mn(II)-Br(V) reaction. It results in an intermediate complex, which subsequently decomposes to the products. At higher [citric acid], the ratio of 1:2 and 1:1 Mn(II)-citric acid complexes reached 1.98. The effects of [pyrophosphate], [LiF], dielectric constant of the media and ionic strength are also in accordance with the proposed mechanism. Reaction constants involved in the proposed mechanism have been evaluated and thermodynamic parameters computed.
Page(s): 407-415
ISSN: 0376-4710
Source:IJC-A Vol.46A(03) [March 2007]

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