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Detection of the Short-Lived Cation Radical Intermediate in the Electrochemical Oxidation ofN,N-Dimethylaniline by Scanning Electrochemical Microscopy
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2014-12-17 , DOI: 10.1021/ja511602v
Fahe Cao 1 , Jiyeon Kim 1 , Allen J. Bard 1
Affiliation  

The short-lived intermediate N,N-dimethylaniline (DMA) cation radical, DMA(•+), was detected during the oxidation of DMA in MeCN with 0.1 M tetra-n-butylammonium hexafluorophosphate. The detection was accomplished at steady state by scanning electrochemical microscopy (SECM) with ultramicroelectrodes using the tip generation/substrate collection mode. Cyclic voltammetry (CV) with a 2 mm Pt electrode indicates that DMA oxidation in acetonitrile is followed by a dimerization and two electrochemical reactions, which is consistent with previous results. The DMA(•+) intermediate is detected by SECM, where the DMA(•+) generated at the ca. 500 nm radius Pt tip is collected on a 5 μm radius Pt substrate when the gap between the tip and the substrate is a few hundred nanometers. Almost all of the DMA(•+) is reduced at the substrate when the gap is 200 nm or less, yielding a dimerization rate constant of 2.5 × 10(8) M(-1)·s(-1) based on a simulation. This is roughly 3 orders of magnitude larger than the value estimated by fast-scan CV. We attribute this discrepancy to the effects of double-layer capacitance charging and adsorbed species in the high scan rate CV.

中文翻译:

N,N-二甲基苯胺电化学氧化中短寿命阳离子自由基中间体的扫描电化学显微镜检测

短寿命中间体 N,N-二甲基苯胺 (DMA) 阳离子自由基 DMA(•+) 在 MeCN 中用 0.1 M 四正丁基六氟磷酸铵氧化 DMA 期间被检测到。使用尖端生成/基板收集模式,通过扫描电化学显微镜 (SECM) 和超微电极在稳态下完成检测。使用 2 mm Pt 电极的循环伏安法 (CV) 表明乙腈中的 DMA 氧化之后是二聚化和两个电化学反应,这与之前的结果一致。DMA(•+) 中间体由SECM 检测,其中DMA(•+) 在大约生成。当尖端和衬底之间的间隙为几百纳米时,500 nm 半径的铂尖端被收集在 5 μm 半径的铂衬底上。当间隙为 200 nm 或更小时,几乎所有的 DMA(•+) 在基板上都减少,基于模拟产生 2.5 × 10(8) M(-1)·s(-1) 的二聚化速率常数. 这大约比快速扫描 CV 估计的值大 3 个数量级。我们将这种差异归因于高扫描速率 CV 中双层电容充电和吸附物质的影响。
更新日期:2014-12-17
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