ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF CATION RADICALS .3. REACTION PATHWAYS OF CARBAZOLIUM RADICAL IONS
ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF CATION RADICALS .3. REACTION PATHWAYS OF CARBAZOLIUM RADICAL IONS
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DOI：
10.1149/1.2134365
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发表时间：
1975-01-01
影响因子：
3.9
通讯作者：
NELSON, RF
中科院分区：
文献类型：
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作者：
AMBROSE, JF;CARPENTER, LL;NELSON, RF
以前的工作已经阐明了咔唑和几种n取代衍生物的阳极氧化途径。这些研究现在已经扩展到76个环取代咔唑，利用电化学和光谱技术来研究各种取代咔唑阳离子自由基的反应性。一般发现3、6、9 (N)位反应性极强；如果这些位点没有被惰性取代基阻断，则电解氧化产生的阳离子自由基通过偶联-脱质子迅速反应。在某些情况下，取代基从阳离子自由基的3和6位被消除，然后偶联形成取代的双脲基。在其他情况下，获得相对稳定的阳离子自由基，并记录其EPR和可见吸收光谱。结果表明，由于咔唑环的平面性，取代咔唑阳离子自由基的反应活性明显高于类似的二苯胺和三苯胺离子。咔唑在过去是一个相对不重要的分子，由于在聚合研究中使用取代咔唑和作为唑唑胺引起的麻痹的抑制剂，目前引起了相当大的兴趣(1)。此外，多环咔唑已被许多工人确定为致癌物质（2-4），甲基取代咔唑已从香烟烟雾中分离出来（5,6）。由于这些分子的致癌活性可能与其氧化还原特性有关，并且考虑到目前和未来的研究可能会验证我们环境中其他取代咔唑的存在，因此认为有必要对许多不同取代咔唑的阳极氧化途径进行广泛的调查。由于溶解度问题，这些研究仅限于非水介质，即乙腈。这项工作也旨在为研究简单和生物重要的吲哚的氧化行为奠定基础。初步的研究表明，吲哚及其衍生物在阳极氧化中具有极强的活性，因此希望通过对活性较低的咔唑的研究获得大量的背景知识。由于涉及的化合物较多，取代模式以及取代基对咔唑阳离子自由基反应途径的影响被普遍阐明；然而，有几种化合物尚未完全表征，因此必须等待进一步、更详细的研究才能完全披露。由于这种调查性质，对所涉及的机制和产品的猜测获得了相当大的许可；正在进行的研究有望反驳或证实这些猜测，但无论如何，人们觉得这些想法至少是可信的，而且往往是可能的。先前的研究已经证实，咔唑在阳极氧化时，形成一个非常不稳定的阳离子自由基，通过偶联-去质子反应生成9,9 ‘和3,3 ’-双脲基；人们认为会形成8种更高的聚合物
Previous work had elucidated the anodic oxidation pathways of carbazole and several N-substituted derivatives. These studies have now been extended to seventy-six ring-substituted carbazoles using electrochemical and spectroscopic techniques to study the reactivity of the various substituted carbazole cation radicals. Generally, it was found that 3, 6, and 9 (N) positions are extremely reactive; if these sites are not blocked by inert substituents the cation radicals generated by electrolytic oxidation react rapidly via coupling-deprotonation. In some cases, substituents are eliminated from the 3 and 6 positions in the cation radicals followed by coupling to form substituted bicarbazyls. In other cases, relatively stable cation radicals were obtained and their EPR and visible absorption spectra were recorded. It was found that the reactivities of substituted carbazole cation radicals are considerably greater than those of analogous di-and triphenylaminium ions due to the planarity of the carbazole aromatic rings.Carbazole, a relatively unimportant molecule in the past, is of considerable interest at present due to the uses of substituted carbazoles in polymerization studies and as inhibitors of zoxazolamine-induced paralysis (1). In addition, polycyclic carbazoles have been established as carcinogenic agents by a number of workers (2-4) and methyl-substituted carbazoles have been isolated from cigarette smoke (5, 6). Since the carcinogenic activity of these molecules may be associated with their redox properties, and considering that present and future studies may verify the presence of other substituted carbazoles in our environment, it was deemed desirable to carry out a broad survey of the anodic oxidation pathways of a number of variously substituted carbazoles. Due to solubility problems, these studies were limited to nonaqueous media, namely acetonitrile. This work is also designed to serve as a basis for investigating the oxidation behavior of simple and biologically important indoles. Preliminary work has shown that indole and its derivatives are extremely reactive upon anodic oxidation, so it was hoped that a good deal of background knowledge could be obtained from studies of the less reactive carbazoles. Due to the large number of compounds involved, substitution patterns as well as substituent effects upon the reaction pathways of the carbazole cation radicals were generally elucidated; however, several compounds have been incompletely characterized and so full disclosure must await further, more detailed investigations. Because of this survey nature, considerable license has been taken with regard to speculation on the mechanisms and products involved; on-going studies will hopefully refute or verify these speculations but in any case it is felt that the ideas forwarded are at least plausible and often likely. Previous work had established that carbazole, upon anodic oxidation, forms a very unstable cation radical that reacts via coupling-deprotonation to 9, 9'-and 3, 3'-bicarbazyls; 8 higher polymers were thought to form