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IJC-A Vol.46A [2007] >
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 Code: | Int. 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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