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Regioselectivity of Electrophilic Additions-Peroxide Effect02:35

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In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
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Sharpless Epoxidation

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The conversion of allylic alcohols into epoxides using the chiral catalyst was discovered by K. Barry Sharpless and is known as Sharpless epoxidation. The use of a chiral catalyst enables the formation of one enantiomer of the product in excess. This chiral catalyst is mainly a chiral complex of titanium tetraisopropoxide and tartrate ester (specific stereoisomer). The stereoisomer used in the chiral catalyst dictates the formation of the enantiomer of the product. In other words, the use of...
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Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
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Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
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在激活的Rh化Pd上选择性电气化基基氧化

Jianan Erick Huang1, Yiqing Chen1, Pengfei Ou1

  • 1Department of Electrical and Computer Engineering, University of Toronto, 35 St George Street, Toronto, Ontario M5S 1A4, Canada.

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现在可再生的二醇 (PG) 电合成效率更高. 一种新型的催化剂与补充改善了选择性和稳定性,在100小时内实现了75%的PG生产率.

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科学领域:

  • 电化学
  • 催化剂
  • 可持续的化学

背景情况:

  • 二醇 (PG) 的生产是碳密集型的.
  • 目前的电合成方法对PG的选择性很低.
  • 化学制造业的脱碳至关重要.

研究的目的:

  • 在电合成中增强二醇选择性.
  • 研究改善PG生产的催化剂机制.
  • 开发一种可再生化学合成的稳定高效的电催化剂.

主要方法:

  • 的电催化氧化
  • 涉及 (Pd) 和 (Rh) 兴奋剂的机制研究.
  • 密度函数理论 (DFT) 的计算.
  • 长期运行稳定性测试 (100小时).

主要成果:

  • 形成了一个转移稳定的PdO氧化层,提高了活性和选择性.
  • 兴奋剂显著增强了PG选择性.
  • 在PG生产中实现了75%的法拉基效率.
  • 催化剂经过100小时的稳定运行.

结论:

  • 可再生能源的电合成可以有效地产生甘醇.
  • 开发的Rh-doped Pd催化剂为可持续的PG制造提供了一个有前途的途径.
  • 了解催化剂表面重建是优化电催化过程的关键.