Electrochemical Polymerization of Aniline Investigated Using On-Line Electrochemistry/Electrospray Mass Spectrometry
作者:Haiteng Deng、Gary J. Van Berkel
DOI:10.1021/ac990527y
日期:1999.10.1
A thin-layer electrochemical flow cell coupled on-line with electrospray mass spectrometry (EC/ES-MS) was used to investigate the soluble products from the controlled-potential anodic polymerization of aniline in H2O and H2O/CH3OH (1/1 v/v) with ammonium acetate and acetic acid or ammonium hydroxide as electrolytes (pH 4, 6.5, or 9). At a working electrode (glassy carbon) potential of 1.0 V versus Ag/AgCl, singly protonated aniline oligomers containing as many as 10 aniline units (10-mer) were observed in the ES mass spectra when the polymerization in H2O/CH3OH at pH 4 was carried out. The abundance of the higher n-mers decreased at higher solution pH and in 100% H2O at pH 4. Most of the oligomers were observed in more than one redox state ranging from fully oxidized (all imine nitrogens) to fully reduced (all amine nitrogens). The number of different redox states observed for the n-mers increased with increasing n. The structures of the reduced (m/z 185) and oxidized (m/z 183) aniline dimer ions (head-to-tail, tail-to-tail, or head-to-head) produced from the polymerization of aniline at pH 4, 6.5, and 9 in H2O/CH3OH were revealed to vary as a function of pH by comparison of their tandem mass spectrometry product ion spectra with the product ion spectra of the dimer standards. EC/ES-MS potential scan experiments, in which the working electrode current and major n-mer ions for n = 2, 3, and 4 were monitored as a function of electrode potential, were used to probe the growth mechanism to higher aniline oligomers. Under the conditions used, the controlled-current electrolytic process inherent to the operation of the ES ion source did not significantly influence the formation or nature of the oligomers observed. Beyond the current application, the results presented here serve to demonstrate the utility of EC/ES-MS as a tool in identifying the initial products of electropolymerization and in studying the products of electrode reactions in general.
使用薄层电化学流动池与电喷雾质谱 (EC/ES-MS) 在线耦合来研究苯胺在 H2O 和 H2O/CH3OH (1/1 v/ v) 用乙酸铵和乙酸或氢氧化铵作为电解质(pH 4、6.5 或 9)。在相对于 Ag/AgCl 的工作电极(玻璃碳)电位为 1.0 V 的情况下,当在 pH 4 的 H2O/CH3OH 中聚合时,在 ES 质谱中观察到含有多达 10 个苯胺单元(10 聚体)的单质子化苯胺低聚物进行了。在较高溶液 pH 值和 pH 4 的 100% H2O 中,较高 n 聚体的丰度降低。观察到大多数低聚物处于不止一种氧化还原状态,范围从完全氧化(所有亚胺氮)到完全还原(所有胺氮) )。观察到的 n-mers 不同氧化还原态的数量随着 n 的增加而增加。 pH 值下苯胺聚合产生的还原 (m/z 185) 和氧化 (m/z 183) 苯胺二聚体离子(头对尾、尾对尾或头对头)的结构通过将串联质谱产物离子谱与二聚体标准品的产物离子谱进行比较,发现 H2O/CH3OH 中的 4、6.5 和 9 作为 pH 函数而变化。 EC/ES-MS 电位扫描实验,其中工作电极电流和 n = 2、3 和 4 的主要 n 聚体离子作为电极电位的函数进行监测,用于探测更高苯胺低聚物的生长机制。在所使用的条件下,ES 离子源操作固有的受控电流电解过程不会显着影响观察到的低聚物的形成或性质。除了当前的应用之外,这里提出的结果还证明了 EC/ES-MS 作为识别电聚合初始产物和研究一般电极反应产物的工具的实用性。