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Nucleophilic Reactivities of Hydrazines and Amines: The Futile Search for the α?Effect in Hydrazine Reactivities

机译:肼和胺类的亲核反应性:对肼反应性中的α?作用的徒劳搜索

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摘要

The kinetics of the reactions of amines, hydrazines, hydrazides, andnhydroxylamines with benzhydrylium ions and quinone methides were studied innacetonitrile and water by UV−vis spectroscopy, using conventional spectrometersnand stopped-flow and laser-flash techniques. From the second-order rate constantsnk2 of these reactions, the nucleophilicity parameters N and sN were determinednaccording to the linear free energy relationship log k2 = sN(N + E). While methylngroups increase the reactivities of the α-position of hydrazines, they decrease thenreactivities of the β-position. Despite the 102 times lower reactivities of amines andnhydrazines in water than in acetonitrile, the relative reactivities of differentlynsubstituted amines and hydrazines are almost identical in the two solvents. In bothnsolvents hydrazine has a reactivity similar to that of methylamine. This observationnimplies that replacement of one hydrogen in ammonia by Me increases thennucleophilicity more than introduction of an amino group, if one takes into account that hydrazine has two reactive centers. Plotsnof log k2 versus the corresponding equilibrium constants (log K) or Brønsted basicities (pKaH) do not show enhancednnucleophilicities (α-effect) for either hydrazines or hydroxylamine relative to alkylamines.
机译:胺,肼,酰肼和正羟胺与二苯甲基铵离子和醌甲基化物的反应动力学通过紫外可见分光光度法在乙腈和水中进行了研究,采用常规分光光度计和定流和激光闪光技术。根据这些反应的二阶速率常数nk2,根据线性自由能关系log k2 = sN(N + E)确定亲核参数N和sN。尽管亚甲基增加了肼的α-位置的反应性,但是它们却降低了β-位置的反应性。尽管胺和联苯胺在水中的反应性比乙腈低102倍,但两种溶剂中不同取代的胺和肼的相对反应性几乎相同。在两种溶剂中,肼的反应性都与甲胺类似。该观察结果暗示,如果考虑到肼具有两个反应中心,那么用Me代替氨中的一个氢,则亲核性会比引入氨基更大。 log k2相对于相应的平衡常数(log K)或Brønsted碱度(pKaH)的图没有显示出肼或羟胺相对于烷基胺的增强的亲核性(α效应)。

著录项

  • 来源
    《The Journal of Organic Chemistry》 |2012年第18期|8142-8155|共14页
  • 作者单位

    Department Chemie Ludwig-Maximilians-Universität München Butenandtstrasse 5-13 (Haus F) 81377 München Germany;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
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  • 入库时间 2022-08-17 13:29:36

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