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首页> 外文期刊>Journal of Physical Organic Chemistry >Kinetics and mechanism of the reaction between 4-hexadecylbenzenediazonium ions and vitamin C in emulsions: further evidence of the formation of diazo ether intermediates in the course of the reaction
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Kinetics and mechanism of the reaction between 4-hexadecylbenzenediazonium ions and vitamin C in emulsions: further evidence of the formation of diazo ether intermediates in the course of the reaction

机译：乳液中4-十六烷基苯重氮离子与维生素C反应的动力学和机理：反应过程中重氮醚中间体形成的进一步证据

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摘要

The kinetics and mechanism of the reaction between hydrophobic 4-hexadecylarenediazonium ions, 16-ArN2+ and vitamin C, VC, in a model emulsion prepared by mixing octane, acidic (HCl) water and the non-ionic surfactant hexaethyleneglycol monododecyl ether, C12E6, were investigated. Because emulsions are opaque, linear sweep voltammetry, LSV, was employed to monitor the reaction. Voltammograms of 16-ArN2+ in emulsions show two reduction peaks as in aqueous systems. The half-life for the spontaneous decomposition of 16-ArN2+ in the emulsion was estimated as t(1/2) = 14.5 h at T = 25 degrees C. Upon addition of VC to the system, the first reduction peak of 16-ArN2+ disappears almost immediately and a new reduction peak is detected at E-p = -0.25 V. Electrochemical titration of 16-ArN2+ shows that the new peak corresponds to the formation of a 1:1 adduct. The i(p)(Ep -0.25 V) values can be linearly correlated with [16-ArN2+] and the observed rate constants, k(obs), were determined by fitting the (i(p), t) data to the integrated first order equation. The variation of k(obs) with [VC] follows a saturation kinetics profile, consistent with the formation of an intermediate in a pre-equilibrium step. All the evidence is consistent with a reaction mechanism comprising two competitive pathways, the spontaneous D-N + A(N) mechanism and the unimolecular decomposition of a transient diazo ether (DE) formed in a pre-equilibrium step. The data allowed estimations of the interfacial rate constant for the reaction between 16-ArN2+ and VC- but did not allow the determination of the equilibrium constant for the DE formation.
机译：在通过混合辛烷，酸性（HCl）水和非离子表面活性剂六乙二醇单十二烷基醚C12E6制备的模型乳液中，疏水性4-十六烷基二烯化氮鎓离子16-ArN2 +与维生素C，VC之间的反应动力学和机理为调查。由于乳液是不透明的，因此采用线性扫描伏安法（LSV）监测反应。乳液中16-ArN2 +的伏安图显示了两个还原峰，如在水性体系中一样。乳液中16-ArN2 +自发分解的半衰期在T = 25摄氏度时估计为t（1/2）= 14.5 h。向系统中添加VC后，16-ArN2 +的第一个还原峰几乎立即消失，并在Ep = -0.25 V处检测到新的还原峰。16-ArN2 +的电化学滴定表明，新峰对应于1：1加合物的形成。 i（p）（Ep -0.25 V）值可以与[16-ArN2 +]线性相关，并且通过将（i（p），t）数据拟合到积分值可以确定观察到的速率常数k（obs）一阶方程。 k [obs]与[VC]的变化遵循饱和动力学曲线，这与在预平衡步骤中形成中间体一致。所有证据均与包含两个竞争途径的反应机理一致，即自发的D-N + A（N）机理和在预平衡步骤中形成的瞬态重氮醚（DE）的单分子分解。数据允许估计16-ArN2 +和VC-之间反应的界面速率常数，但不能确定DE形成的平衡常数。

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