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Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene

Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene

Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...

α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction

α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction

The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the Hell–Volhard–Zelinski reaction. The reaction is catalyzed by phosphorus tribromide, which can be used directly or produced in situ from red phosphorus and bromine. The mechanism comprises PBr3 catalyzed conversion of acid to acid bromide and hydrogen bromide. The acid bromide enolizes to its enol form in the presence of HBr. The nucleophilic enol attacks the bromine molecule...

Halogenation of Alkenes

Halogenation of Alkenes

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.

Radical Substitution: Allylic Bromination

Radical Substitution: Allylic Bromination

In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...

Preparation and Reactions of Sulfides

Preparation and Reactions of Sulfides

Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.

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Related Experiment Video

Updated: Jul 8, 2026

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates

Published on: March 6, 2019

[A new bromine-containing reagent for cysteine modification].

T V Minaeva, E N Danilovtseva, V V Annenkov

Bioorganicheskaia Khimiia

|January 5, 2008

Summary

A new reagent, 5-Bromo-2[(2-iodoacetyl)amino]benzenesulfonic acid (AIBSA), was synthesized to modify cysteine thiol groups in proteins. Its stability and unique bromine signature aid in identifying labeled peptides via mass spectrometry.

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Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

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Last Updated: Jul 8, 2026

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates

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Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

Published on: September 28, 2022

Area of Science:

Biochemistry
Chemical Biology
Proteomics

Context:

Cysteine thiol groups are crucial in protein structure and function.
Specific chemical reagents are needed for selective protein modification.
Mass spectrometry is a key tool for analyzing peptides and proteins.

Purpose:

To synthesize and characterize a novel reagent for cysteine modification.
To determine the reactivity of the new reagent with thiol groups.
To establish a method for identifying modified peptides using mass spectrometry.

Summary:

5-Bromo-2[(2-iodoacetyl)amino]benzenesulfonic acid (AIBSA) was synthesized as a reagent for modifying free cysteine thiol groups.
Rate constants for AIBSA's interaction with thiols were determined, indicating its reactivity.
The bromine atom in AIBSA provides a unique isotopic signature for easy identification of labeled peptides in mass spectra.

Impact:

Provides a stable and light-resistant reagent for protein and peptide analysis.
Facilitates the identification of cysteine-modified peptides in complex biological samples.
Enhances the utility of mass spectrometry in proteomics research by enabling specific labeling strategies.