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

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

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[IO4-]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-])[IO4-]tot+K1｝,在25.0℃及离子强度0.30mol·L-1时,对此反应有ka=(2.6±1.2)×10-2mol-1·L·s-1,kb=(2.8±0.1)mol-2·L2·s-1,及K1=(4.1±0.4)×10-4mol·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.

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 [IO4^-]tox had a significant influence on the reaction rates, where [IO4^-]tox denotes the total concentration of periodate added externally. An empirical rate expression, k＇=（ka＋kb[OH^-]）K1/{f[OH^-]）[IO4^-]（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 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.