二(氢过碘酸)合银(III)配离子氧化愈创甘油醚的反应动力学及机理

在碱性介质中, 用传统的分光光度法研究了Ag(III)配离子, 即[Ag(HIO6)2]5-, 氧化药物分子愈创甘油醚的动力学及其机理. 用质谱鉴定了氧化产物；反应对Ag(III) 和愈创甘油醚均为一级；在温度25.0-40.0 ℃范围内, 通过分析[OH-]和[IO-4]tot对反应速率的影响, 二级速率常数有以下表达式：k′=(ka+kb[OH-])K1/{f([OH-])[IO-4]tot+K1}, 在25.0 ℃及离子强度0.30 mol·L-1时, 对此反应有ka=(2.6±1.2)×10-2 mol-1·L·s-1, kb=(2.8±0.1) mol-2·L2·s-1, 及K1=(4.1±0.4)×10-4 mol·L-1, 求出了涉及ka, kb的活化参数, 并据此推出反应机理为反应体系中的[Ag(HIO6)2]5-配离子在前期平衡后, 反应活性中心与药物分子形成Ag(III)-过碘酸-愈创甘油醚分子三元配合物, 配位甘油醚分子通过两个平行途径将两电子传递给中心原子Ag：一个途径无OH-离子参与, 另一途径有OH-参与完成.

Mechanism and Kinetics of Guaifenesin Oxidation by Bis(hydrogen periodato)argentate(Ⅲ) Complex Anion

Oxidation of the drug guaifenesin by a Ag(III) complex anion, [Ag(HIO6)2]5-, was studied in aqueous alkaline medium by using spectrophotometry. The major oxidation product of guaifenesin was identified by mass spectrometry. The oxidation reaction displayed an overall second-order kinetics: first-order with respect to both Ag(III) and guaifenesin. Variations of [OH-] and [IO-4]tot had a significant influence on the reaction rates, where [IO-4]tot denotes the total concentration of periodate added externally. An empirical rate expression, k′=(ka+kb[OH-])K1/{f([OH-])[IO-4]tot+K1}, was derived, where ka=(2.6±1.2)×10-2 mol-1·L·s-1, kb=(2.8±0.1) mol-2·L2·s-1, and K1=(4.1±0.4)×10-4 mol·L-1 at 25.0 ℃ and ionic strength of 0.30 mol·L-1. Activation parameters associated with ka and kb were also derived. A mechanism involving the [Ag(HIO6)(OH)(H2O)]2- as the reactive species of the oxidant was proposed. Guaifenesin and the reactive species reversibly formed a complex, which decomposed by two parallel slow steps to give rise to the products: one pathway was spontaneous and the other was assisted by a hydroxide ion.