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Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC PDF Download

Introduction

Chugaev reaction mechanism is a concerted process, which has been discussed below along with its application and limitation. Chugaev reaction was first of all reported by Chugaev in 1899. It is a type of elimination reaction, also known as pyrolytic elimination.

Chugaev reaction

  • Alcohol reacts with carbon disulfide in presence of sodium hydroxide to give sodium xanthate, which on further alkylation with methyl iodide (generally) gives xanthate ester. This xanthate upon pyrolysis produces olefin or alkene. Thus, the conversion of alcohol into olefin by the corresponding xanthate esters is called Chugaev reaction. This reaction is also known as Chugaev elimination or Chugaev xanthate reaction.
    Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC
  • This reaction is very useful for the conversion of secondary and tertiary alcohol into an alkene. You may have questions on your head, why primary alcohol is not suitable for this purpose? right. Its because the xanthate ester of primary alcohol generally has high thermal stability therefore, it is difficult to decompose by heating.
    • This pyrolysis takes place via an intramolecular cis-elimination without the rearrangement of carbon framework.

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What is the Chugaev reaction?
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Chugaev reaction mechanism

The mechanism of Chugaev reaction is discussed below.

Step 1: Formation of xanthate ester

In this process, alcohol reacts with CS2 in presence of NaOH, followed by alkylation produces xanthate ester.
Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC

Step 2: Pyrolysis of xanthate ester.

This step is a concerted process, which takes place in presence of heat. Actually, this step is the Chagaev reaction in which the pyrolysis of xanthate ester takes place.
Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC

Some examples of Chugaev Reaction

Let’s see examples of this reaction.
Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC

Question for Chugaev Reaction and Mechanism
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Which of the following is a limitation of the Chugaev reaction?
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Application of Chugaev reaction

This reaction can be used for the preparation of different types of olefins including bornylene, menthene, etc.

Limitation

If the Beta-carbon contains more than one hydrogen or if the elimination is possible in more than one position, a mixture of isomeric olefins is produced. For example,
Chugaev Reaction and Mechanism | Chemistry Optional Notes for UPSC

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FAQs on Chugaev Reaction and Mechanism - Chemistry Optional Notes for UPSC

1. What is the Chugaev reaction?
The Chugaev reaction is a chemical reaction that involves the conversion of an aromatic diazonium salt into a corresponding aryl fluoride through the reaction with hydrogen fluoride (HF) or a fluoride source. It is named after the Russian chemist Alexander Chugaev, who first reported this reaction in the early 20th century.
2. What is the mechanism of the Chugaev reaction?
The Chugaev reaction proceeds through a nucleophilic aromatic substitution (S​NAr) mechanism. The diazonium salt reacts with hydrogen fluoride (HF) or a fluoride source to generate a fluoronium ion intermediate. This intermediate then undergoes an S​NAr reaction with the aromatic ring to replace the diazonium group with a fluorine atom, resulting in the formation of an aryl fluoride.
3. Can you provide some examples of the Chugaev reaction?
Certainly! Here are a few examples of the Chugaev reaction: 1. Conversion of benzenediazonium chloride to fluorobenzene using hydrogen fluoride (HF) as the fluorinating agent. 2. Transformation of 4-nitrobenzenediazonium chloride to 4-fluoronitrobenzene using potassium fluoride (KF) as the fluoride source. 3. Synthesis of 2-chloro-5-fluorotoluene from the corresponding benzenediazonium salt and hydrogen fluoride (HF). 4. Conversion of 2,4-dinitrobenzenediazonium chloride to 2,4-dinitrofluorobenzene using a fluoride source like cesium fluoride (CsF). 5. Preparation of 2-fluoro-5-nitroaniline by reacting 2-nitrobenzenediazonium chloride with hydrogen fluoride (HF).
4. How is the Chugaev reaction relevant to the UPSC exam?
The Chugaev reaction is a significant topic in organic chemistry, and its understanding is crucial for students preparing for the UPSC exam in the field of chemistry. Questions related to reaction mechanisms, transformations, and applications of the Chugaev reaction may be asked in the exam to test the candidates' knowledge of organic chemistry and their ability to apply it in various contexts.
5. What are some common FAQs about the Chugaev reaction?
1. Is the Chugaev reaction limited to the synthesis of aryl fluorides? 2. Can other halogens be used instead of fluorine in the Chugaev reaction? 3. What are the advantages of using the Chugaev reaction compared to other fluorination methods? 4. Are there any limitations or challenges associated with the Chugaev reaction? 5. Can the Chugaev reaction be applied to the synthesis of complex organic molecules?
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