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Acid-Catalyzed α-Halogenation of Aldehydes and Ketones01:21

Acid-Catalyzed α-Halogenation of Aldehydes and Ketones

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By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
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Base-Promoted α-Halogenation of Aldehydes and Ketones00:51

Base-Promoted α-Halogenation of Aldehydes and Ketones

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α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base.  The reaction begins with the abstraction of  α hydrogen by the base to produce a nucleophilic enolate ion. This intermediate undergoes a subsequent nucleophilic substitution with the halogen to produce a monohalogenated carbonyl compound. If the starting substrate has more than one α hydrogen, it is difficult to stop the reaction...
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Multiple Halogenation of Methyl Ketones: Haloform Reaction01:28

Multiple Halogenation of Methyl Ketones: Haloform Reaction

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A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with the deprotonation of α hydrogen to form an enolate ion which reacts with the electrophilic halogen to give an α-halo ketone. The step continues until all the α protons are substituted to form a trihalomethyl ketone. The resulting molecule is unstable, and in the presence of a hydroxide base, it readily undergoes nucleophilic...
2.7K
Preparation of Alkynes: Dehydrohalogenation02:34

Preparation of Alkynes: Dehydrohalogenation

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Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
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Halogenation of Alkenes02:46

Halogenation of Alkenes

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Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
18.1K
α-Halogenation of Carboxylic Acid Derivatives: Overview01:14

α-Halogenation of Carboxylic Acid Derivatives: Overview

3.9K
Unlike aldehydes and ketones, carboxylic acids do not readily participate in α halogenation reactions via enols or enolate intermediates. However, α-halogenated acids are obtained through other methods. One of the approaches is the Hell–Volhard–Zelinsky (HVZ) reaction, wherein the carboxylic acid is treated with halogen in the presence of PBr3. It involves the conversion of acid to acid halide, which exists in equilibrium with its enol form. The enol attacks the...
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[Recent progress in 2-haloacid dehalogenases].

Yayue Wang1, Song Xue2, Qingfeng Zhou1

  • 1College of Biology and Food, Shangqiu Normal University, Shangqiu 476000, Henan, China.

Sheng Wu Gong Cheng Xue Bao = Chinese Journal of Biotechnology
|June 23, 2020
PubMed
Summary
This summary is machine-generated.

2-Haloacid dehalogenases are enzymes that remove halogens from compounds, aiding in pollutant degradation and chiral compound synthesis. This review covers their sources, structures, mechanisms, and applications.

Keywords:
2-haloacid dehalogenasesapplicationcatalytic mechanismprotein structure

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Area of Science:

  • Biochemistry
  • Environmental Science
  • Green Chemistry

Background:

  • 2-Haloacid dehalogenases (EC 3.8.1.X) catalyze hydrolytic dehalogenation of 2-haloacids.
  • These enzymes produce 2-hydroxyacids and halogen ions.
  • They are crucial for degrading halogenated pollutants and synthesizing chiral compounds.

Purpose of the Study:

  • To review recent advancements in 2-haloacid dehalogenases.
  • To cover their sources, protein structures, reaction mechanisms, catalytic properties, and applications.
  • To suggest future research directions.

Main Methods:

  • Biochemical characterization of various 2-haloacid dehalogenases.
  • Analysis of protein crystal structures.
  • Investigation of catalytic mechanisms.

Main Results:

  • 2-Haloacid dehalogenases exhibit a broad substrate profile.
  • They demonstrate high efficiency in enantiomer resolution.
  • These enzymes are valuable for environmental remediation and green synthesis.

Conclusions:

  • 2-Haloacid dehalogenases are versatile biocatalysts with significant environmental and synthetic applications.
  • Further research can enhance their utility in pollutant degradation and chiral synthesis.
  • Continued study of their structures and mechanisms will unlock new applications.