Kinetics and mechanism of oxidation of a ternary complex involving dipicolinatochromium(III) and DL-aspartic acid by N-bromosuccinimide

✍ Scribed by Hassan A. Ewais; Ahmed E. Ahmed; Ahmed A. Abdel-Khalek

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 109 KB
• Volume: 36
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20014

✦ Synopsis

Abstract

The kinetics of oxidation of [Cr^III^(Dpc)(Asp)(H~2~O)~2~] (Dpc = dipicolinic acid and Asp = DL‐aspartic acid) by N‐bromosuccinimide (NBS) in aqueous solution have been found to obey the equation:

equation image

where k~2~ is the rate constant for the electron transfer process, K~1~ is the equilibrium constant for deprotonation of [Cr^III^(Dpc)(Asp)(H~2~O)~2~], K~2~ and K~3~ are the pre‐equilibrium formation constants of precursor complexes [Cr^III^(Dpc)(Asp)(H~2~O)(NBS)] and [Cr^III^(Dpc)(Asp)(H~2~O)(OH)(NBS)]^−^. Values of k~2~ = 4.85 × 10^−2^ s^−1^, K~1~ = 1.85 × 10^−7^ mol dm^−3^, and K~2~ = 78.2 mol^−1^ dm^3^ have been obtained at 30°C and I = 0.1 mol dm^−3^. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr^III^(Dpc)(Asp)(H~2~O)(OH)]^−^ is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 394–400, 2004