Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anion |
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Authors: | Shigang Shen Hongmei Shi Hanwen Sun |
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Institution: | 1. College of Chemistry and Environmental Science, Hebei University, Baoding 071002, Hebei Province, People's Republic of China;2. College of Chemistry and Environmental Science, Hebei University, Baoding 071002, Hebei Province, People's Republic of ChinaCollege of Chemistry and Environmental Science, Hebei University, Baoding 071002, Hebei Province, People's Republic of China |
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Abstract: | Mephenesin is being used as a central‐acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, Ag(HIO6)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′ = (ka + kbOH?])K1/{f(OH?])IO?4]tot + K1}, where IO?4]tot denotes the total concentration of periodate, ka = (1.35 ± 0.14) × 10?2M?1s?1 and kb = 1.06 ± 0.01 M?2s?1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with ka and kb 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 |
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