Kinetics and Mechanism for Oxidation of L-Proline by Bis(hydrogen periodato)argentate(III) Complex Anion

✍ Scribed by Han-Wen SUN; Hong-Mei SHI; Shi-Gang SHEN; Wei-Jun KANG; Zhi-Feng GUO

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 139 KB
• Volume: 26
• Category: Article
• ISSN: 0256-7660
• DOI: 10.1002/cjoc.200890116

✦ Synopsis

Oxidation of L-proline by bis(hydrogen periodato)argentate(III) complex anion, [Ag(HIO 6 ) 2 ] 5-, has been studied in aqueous alkaline medium in the temperature range of 25-40 ℃ by use of conventional spectrophotometry. Under the conditions for kinetic measurements, the oxidation results in decarboxylation of proline, giving rise to γ-aminobutyrate as identified by mass spectrometry. The oxidation kinetics is first order with respect to the silver(III) and proline concentrations; the second-order rate constants, decreasing with increasing [periodate], are essentially independent of [OH -]. The kinetic results were interpreted in terms of a reaction mechanism which involves a pre-equilibrium between [Ag(HIO 6 ) 2 ] 5-and [Ag(HIO 6 )(H 2 O)(OH)] 2-, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced parallelly by the fully deprotonated form of proline in rate-determining steps (described by k 1 for the former Ag(III) and k 2 for the latter one). The determined rate constants and their associated activation parameters are k 1 (25

. This is also the first time to find that [Ag(HIO 6 ) 2 ] 5-is also reactive toward a particular reductant and shows a lower reactivity than [Ag(HIO 6 )(OH)(H 2 O)] 2-.