Mechanism of Phenol Alkylation in Zeolite H-BEA Using In Situ Solid-State NMR Spectroscopy
作者:Zhenchao Zhao、Hui Shi、Chuan Wan、Mary Y. Hu、Yuanshuai Liu、Donghai Mei、Donald M. Camaioni、Jian Zhi Hu、Johannes A. Lercher
DOI:10.1021/jacs.7b02153
日期:2017.7.12
electrophile, the cyclohexyl carbeniumion, is directly formed in a protonation step when cyclohexene is the coreactant. In the presence of cyclohexanol, its protonated dimers at Brønsted acid sites hinder the adsorption of cyclohexene and the formation of a carbeniumion. Thus, it is demonstrated that protonated cyclohexanol dimers dehydrate without the formation of a carbeniumion, which would otherwise
使用原位 13C MAS NMR 光谱研究了固体酸催化苯酚与环己醇和环己烯在非极性溶剂十氢化萘中的烷基化反应机理。只有在大部分环己醇脱水成环己烯后,苯酚与环己醇的烷基化才会开始。由于苯酚和环己醇显示出相似的吸附强度,因此这种严格的反应顺序并不是由于苯酚与环己醇的接触受限,而是由于存在反应性亲电试剂,只要存在大量环己醇。13C 同位素标记表明,当环己烯是共反应物时,反应性亲电子试剂环己基碳正离子在质子化步骤中直接形成。在环己醇存在下,其在 Brønsted 酸位点的质子化二聚体阻碍了环己烯的吸附和碳正离子的形成。因此,证明质子化的环己醇二聚体在不形成碳鎓离子的情况下脱水,否则碳鎓离子将有助于动力学相关步骤中的烷基化。同位素加扰表明环己基苯基醚的分子内重排对芳环的烷基化没有显着贡献。
Unraveling the Dynamic Network in the Reactions of an Alkyl Aryl Ether Catalyzed by Ni/γ-Al<sub>2</sub>O<sub>3</sub>in 2-Propanol
作者:Long Qi、Ali Chamas、Zachary R. Jones、Eric D. Walter、David W. Hoyt、Nancy M. Washton、Susannah L. Scott
DOI:10.1021/jacs.9b09071
日期:2019.10.30
undergoes facile H/D exchange (k3 = 0.046 s-1 gcat-1 at 175 °C). While the source of the reducing equivalents for both hydrogenolysis and hydrogenation is exclusively H2/D2(g) rather than the alcohol solvent at these temperatures, the initial isotopic composition of adsorbed H/D on the catalyst surface is principally determined by the solvent isotopic composition (2-PrOH/D). All reactions are preceded by
A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials
作者:Jan Sehnert、Jürgen Senker
DOI:10.1002/chem.200601726
日期:2007.7.27
isotope labeling with computational methods and different solid-state NMR techniques. We chose triphenylphosphite (TPP) as an interesting example of our investigations because TPP exhibits two crystalline modifications and two different amorphous phases one of which is highly correlated. In particular we analyzed the conformational distribution in three of these phases. A sample of triply labeled 1-[13C]TPP
Synthesis of
<sup>13</sup>
C‐labeled parabens from isotopically enriched phenols using the Houben–Hoesch reaction
作者:Keith P. Reber、John D. Sivey、Matthew Vollmuth、Priyansh D. Gujarati
DOI:10.1002/jlcr.3992
日期:2022.7
environmental concern. In order to identify these transformation products and investigate their mechanism of formation, a synthetic route to ethyl parabens labeled with the stable isotope carbon-13 at specific positions within the benzene ring was developed. This efficient two-step procedure starts from commercially available 13C-labeled phenols and involves (1) initial acylation of the phenol via a Houben–Hoesch
对羟基苯甲酸酯是多种消费品中的抗菌添加剂。然而,在废水消毒过程中由对羟基苯甲酸酯形成的卤代化合物是一个潜在的环境问题。为了识别这些转化产物并研究它们的形成机制,开发了一种在苯环内特定位置用稳定同位素碳 13 标记对羟基苯甲酸乙酯的合成路线。这种有效的两步法从市售的13 C 标记的苯酚开始,包括 (1) 通过与三氯乙腈的 Houben-Hoesch 反应对苯酚进行初始酰化,然后 (2) 对所得三氯甲基酮进行改进的卤仿反应,得到对应13C 标记的对羟基苯甲酸乙酯的总产率为 65%–80%。还研究了改进的卤仿反应的范围,允许合成衍生自伯醇或仲醇的其他对羟基苯甲酸酯,包括13 C-和氘标记的酯。此外,4-羟基苯甲酸可以直接由常见的三氯甲基酮中间体在用氢氧化锂处理后形成。该方案补充了现有的制备13 C 标记的对羟基苯甲酸酯衍生物的方法,并提供了在 Houben-Hoesch 反应(形成对二取代产物)