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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...

Regioselectivity of Electrophilic Additions-Peroxide Effect

Regioselectivity of Electrophilic Additions-Peroxide Effect

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.

Formation of Halohydrin from Alkenes

Formation of Halohydrin from Alkenes

An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.

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...

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...

Radical Anti-Markovnikov Addition to Alkenes: Mechanism

Radical Anti-Markovnikov Addition to Alkenes: Mechanism

The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...

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Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

Published on: November 22, 2016

Bromate formation from bromide oxidation by the UV/persulfate process.

Jing-Yun Fang¹, Chii Shang

¹Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.

Environmental Science & Technology

|July 27, 2012

Summary

Bromate formation during UV/persulfate oxidation is driven by sulfate radicals, increasing with persulfate and bromide levels. Higher pH and natural organic matter in real water significantly reduce bromate production.

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Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

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Area of Science:

Environmental Chemistry
Water Treatment Technologies
Oxidation Processes

Background:

Bromate is a regulated disinfection byproduct.
UV/persulfate is an advanced oxidation process for water treatment.
Understanding bromate formation mechanisms is crucial for safe water.

Purpose of the Study:

Investigate bromate formation during UV/persulfate treatment.
Evaluate the impact of pH, persulfate, and bromide concentrations.
Compare bromate formation in ultrapure and real water.

Main Methods:

Oxidation experiments in ultrapure and real water matrices.
Varied pH, persulfate dosage, and bromide concentration.
Analyzed bromate formation and reaction intermediates.

Main Results:

Bromate formation increased with persulfate dosage and bromide concentration.
Sulfate radicals drive bromate formation via hypobromous acid/hypobromite intermediates.
Bromate formation decreased significantly above pH 7 and was lower in real water due to natural organic matter (NOM).

Conclusions:

UV/persulfate process efficacy for bromate reduction is pH-dependent.
NOM in real water mitigates bromate formation by scavenging reactive species.
Bromate formation and micropollutant degradation are coupled, influenced by NOM presence.