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7.4.2 - Preparation of Phenols

Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Preparation from Haloarenes

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Teacher
Teacher

Today, we're diving into how we can prepare phenols, starting with the conversion of haloarenes. Can anyone tell me how phenol is derived from chlorobenzene?

Student 1
Student 1

Is it through a reaction with sodium hydroxide?

Teacher
Teacher

Exactly! Chlorobenzene reacts with sodium hydroxide when we heat it at high pressures. This reaction forms sodium phenoxide, which can be converted into phenol by acidification. Remember, think of 'high heat, high pressure' for this reaction!

Student 2
Student 2

So, the product sodium phenoxide is a key intermediate?

Teacher
Teacher

That's correct! The sodium phenoxide is crucial for obtaining phenol. Let’s keep it in mind with the acronym SPA: Sodium, Phenoxide, Acid to remember the sequence of reactions!

Preparation from Benzenesulphonic Acid

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Teacher
Teacher

Next, let’s explore how we can prepare phenol from benzenesulphonic acid. Can anyone explain the steps involved?

Student 3
Student 3

Do we start with sulfonation of benzene?

Teacher
Teacher

Correct! After sulfonating benzene, we get benzenesulphonic acid. Heating this with sodium hydroxide produces sodium phenoxide. What comes after that?

Student 4
Student 4

We need to acidify sodium phenoxide to get phenol!

Teacher
Teacher

Exactly! To remember this process, use the mnemonic 'Sodium Sulfone, Acid to Leave.' It's a straightforward way to retain this method.

Preparation from Diazonium Salts

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Teacher
Teacher

Now, let’s cover the preparation of phenols via diazonium salts. Who can summarize how this happens?

Student 1
Student 1

We create a diazonium salt from an aromatic amine, then what?

Teacher
Teacher

Great start! Once you’ve formed the diazonium salt, what happens next?

Student 2
Student 2

It can be hydrolyzed to yield phenol, right?

Teacher
Teacher

Exactly! The hydrolysis of diazonium salts produces phenol. You can remember this with the acronym DAH: Diasonium, Acidify, Hydrolyze.

Industrial Preparation from Cumene

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Teacher
Teacher

Finally, let’s discuss the industrial preparation of phenol from cumene. Why is this method significant?

Student 3
Student 3

Because it produces both phenol and acetone, right?

Teacher
Teacher

Correct! The cumene process is efficient as it yields two valuable products. Can someone explain the steps?

Student 4
Student 4

Cumene is oxidized to hydroperoxide, then acidified?

Teacher
Teacher

Exactly! This method is convenient. Let's remember it as the '2P Process' - Producing two products: Phenol and Acetone.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

Phenols can be prepared from various chemical precursors through several industrial and laboratory methods.

Standard

The preparation of phenols involves methods that utilize haloarenes, benzenesulphonic acid, diazonium salts, and the cumene process. These processes highlight the versatility of aromatic compounds and their reactivity under specific conditions, which are crucial for industrial applications.

Detailed

Preparation of Phenols

Phenols, known for their aromatic character, can be synthesized through various methods.

Methods of Preparation:

  1. From Haloarenes: Chlorobenzene can be converted to phenol by fusing it with sodium hydroxide at high temperature (623K) and high pressure (320 atm). Upon acidification of the resulting sodium phenoxide, phenol is produced.
  2. From Benzenesulphonic Acid: Benzene undergoes sulfonation with oleum to form benzenesulphonic acid, which can then be transformed into sodium phenoxide through heating with molten sodium hydroxide. Acidification of this sodium salt leads to phenol.
  3. From Diazonium Salts: A diazonium salt is created by treating an aromatic primary amine with nitrous acid at low temperatures. This diazonium salt can be hydrolyzed to form phenols upon warm water treatment or through dilute acid treatment.
  4. From Cumene: The major industrial method for producing phenol involves the oxidation of cumene (isopropylbenzene) to cumene hydroperoxide, which, when treated with dilute acid, yields phenol along with acetone as a by-product.

Significance:

The production of phenols is significant in the chemical industry, as they serve as precursors to various chemicals and have applications in fields such as pharmaceuticals, plastics, and antiseptics.

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Audio Book

Dive deep into the subject with an immersive audiobook experience.

Introduction to Phenols

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Phenol, also known as carbolic acid, was first isolated in the early nineteenth century from coal tar. Nowadays, phenol is commercially produced synthetically. In the laboratory, phenols are prepared from benzene derivatives by any of the following methods:

Detailed Explanation

Phenol is an important chemical compound used in various applications, and its industrial production has evolved over time. Initially derived from natural sources like coal tar, phenol is now more commonly produced through synthetic processes. Understanding how phenols are prepared is key for grasping their applications and properties.

Examples & Analogies

Think of phenol like a building block in a factory. Initially, it was obtained from raw materials (coal tar), but as technology advanced, manufacturers developed more efficient methods (synthetic production) to produce it quickly and in large quantities.

Preparation from Haloarenes

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  1. From haloarenes
    Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced.

Detailed Explanation

This method of preparing phenols involves taking chlorobenzene, a compound in which chlorine is attached to a benzene ring, and reacting it with sodium hydroxide (NaOH) at high temperature and pressure. Upon cooling and subsequent reactions, phenol is obtained. This preparation route highlights the substitution reaction where the chlorine atom is replaced by a hydroxyl group, producing phenol.

Examples & Analogies

Imagine replacing a broken part in a machine with a better one. Here, the chlorine (the broken part) is replaced by a hydroxyl group (the better part) during the reaction, improving the functionality of the compound, just like a functional upgrade in machinery.

Preparation from Benzenesulphonic Acid

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  1. From benzenesulphonic acid
    Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.

Detailed Explanation

This preparation involves sulphonating benzene to introduce a sulfonic acid group, which can later be converted to a phenol through a series of reactions, including heating with sodium hydroxide and acidifying the product. This process also emphasizes how functional groups can be modified to create desired compounds.

Examples & Analogies

Consider making a specialty drink by mixing ingredients in specific steps. First, you add a flavor (sulphonation), then you heat it (to transform it), and finally, you add something to enhance its taste (acidification), which eventually gives you the final product, just like preparing phenol from benzenesulphonic acid.

Preparation from Diazonium Salts

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  1. From diazonium salts
    A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2 + HCl) at 273-278 K. Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids.

Detailed Explanation

In this method, an aromatic primary amine reacts with nitrous acid to form a diazonium salt, which is a high-energy intermediate. This salt can be hydrolyzed, or broken down in the presence of water or dilute acid, to yield phenol. This reaction illustrates how diazonium salts serve as important intermediates in organic synthesis.

Examples & Analogies

Think of a diazonium salt as a temporary storage box for items before they are moved into their proper places. Here, the items (phenol) are safely stored in the box (diazonium salt) until conditions are right for them to be moved to the final destination (phenol).

Preparation from Cumene

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  1. From cumene
    Phenol is manufactured from the hydrocarbon, cumene. Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid. Acetone, a by-product of this reaction, is also obtained in large quantities by this method.

Detailed Explanation

Cumene is a hydrocarbon that undergoes oxidation to produce cumene hydroperoxide. This compound can then be converted into phenol and acetone in a single process. The dual production of phenol and acetone from cumene makes this method of preparation commercially significant in the chemical industry.

Examples & Analogies

Imagine a factory that specializes in making two products from one process. Instead of creating one item at a time, the factory can produce both phenol and acetone from cumene, similar to how a bakery might create bread and pastries from the same dough.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Preparation from Haloarenes: Phenol is synthesized by fusing haloarenes with sodium hydroxide.

  • Preparation from Benzenesulphonic Acid: Conversion of benzenesulphonic acid to phenol via sodium phenoxide.

  • Preparation from Diazonium Salts: Hydrolysis of diazonium salts yields phenols.

  • Industrial Preparation: The cumene process produces phenol and acetone.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Phenol is obtained from chlorobenzene through sodium hydroxide at high temperatures.

  • Benzene is sulphonated to benzenesulphonic acid and then treated with sodium hydroxide for phenol synthesis.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • When chlorobenzene meets NaOH, phenol is the straightforward path.

📖 Fascinating Stories

  • Imagine a chemist named Ben who took a trip to find sodium hydroxide to convert chlorobenzene into precious phenol, leading him to the land of aromatic reactions.

🧠 Other Memory Gems

  • Remember 'D.A.H.' for Diazotization, Acidification, Hydrolysis for easy recall of diazonium to phenol.

🎯 Super Acronyms

Use 'C.P.P.' for Cumene Process Phenol, to denote cumene leading to phenol and acetone.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Phenol

    Definition:

    An aromatic compound characterized by a hydroxyl group (-OH) attached to a carbon atom of an aromatic ring.

  • Term: Haloarene

    Definition:

    An aromatic compound containing at least one halogen atom substituent.

  • Term: Diazonium Salt

    Definition:

    A compound containing a diazonium group (-N2^+) that can be formed from aromatic amines.

  • Term: Cumene

    Definition:

    An aromatic hydrocarbon used as a precursor in the production of phenol and acetone.