Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anion

✍ Scribed by Shigang Shen; Hongmei Shi; Hanwen Sun

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 285 KB
• Volume: 39
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20260

✦ Synopsis

Abstract

Mephenesin is being used as a central‐acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO~6~)~2~]^5−^, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3‐(2‐methylphenoxy)‐2‐ketone‐1‐propanol by mass spectrometry. An overall second‐order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH^−^] and periodate concentration on the observed second‐order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced: k′ = (k~a~ + k~b~[OH^−^])K~1~/{f([OH^−^])[IO^−^~4~]~tot~ + K~1~}, where [IO^−^~4~]~tot~ denotes the total concentration of periodate, k~a~ = (1.35 ± 0.14) × 10^−2^M^−1^s^−1^ and k~b~ = 1.06 ± 0.01 M^−2^s^−1^ at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with k~a~ and k~b~ have been calculated. A mechanism has been proposed to involve two pre‐equilibria, leading to formation of a periodato‐Ag(III)‐mephenesin complex. In the subsequent rate‐determining steps, this complex undergoes inner‐sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH^−^ whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre‐equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440–446, 2007