Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 3: Problem 172

Statement 1 Pure phenol is a colourless solid but turns reddish brown on keeping. and Statement 2 Phenol is slowly oxidized by air to quinone.

Short Answer

Expert verified
Answer: Phenol turns reddish-brown over time when exposed to air due to the slow oxidation process that converts phenol to quinone. The formation of quinone causes the reddish-brown color as it absorbs light in the visible spectrum due to its increased conjugation in comparison to phenol.

Step by step solution

01

Understanding the structure of phenol and quinone

Phenol is an aromatic compound with the formula C6H5OH, which consists of a benzene ring with a hydroxyl (-OH) group attached to one of its carbon atoms. Quinone, on the other hand, is an organic compound with the formula C6H4O2. In the case of phenol oxidation, the quinone formed is 1,2-benzoquinone, also called simply 'quinone'. It has a benzene ring with two carbonyl groups (=O) in the 1,2-positions (adjacent carbon atoms).
02

Discussing the oxidation process from phenol to quinone

Over time, when phenol is exposed to air, it undergoes a slow oxidation process. Oxidation is a chemical reaction that involves the loss of electrons. In the case of phenol, the hydroxyl group (-OH) loses its hydrogen atom as a proton, and the remaining oxygen forms a double bond with the benzene ring. This results in the formation of the two carbonyl groups (=O) on the quinone molecule.
03

Explaining how the formation of quinone causes the reddish-brown color in phenol

As phenol slowly oxidizes to quinone in the presence of air, the resulting quinone molecules have a reddish-brown color. This color change is mostly due to the increased conjugation in the quinone molecule as compared to phenol, which causes quinone to absorb light in the visible spectrum. The more quinone that forms in the sample, the more pronounced the reddish-brown color becomes. Therefore, when pure phenol is kept for an extended period, its color turns from colorless to a reddish-brown due to the formation of quinone by slow oxidation in the presence of air.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Sodium phenoxide when heated with \(\mathrm{CO}_{2}\) under pressure gives sodium salicylate. This reaction is known as (a) Reimer-Tiemann reaction (b) Schotten-Baumann reaction (c) Williamson's synthesis (d) Kolbe's reaction

Statement 1 Salicylic acid may be prepared from sodium phenoxide by Kolbe-Schmidt reaction using carbon dioxide. and Statement 2 Kolbe-Schmidt reaction is a nucleophilic substitution reaction.

Ethyl benzene \(\stackrel{\mathrm{NBS}}{\longrightarrow} \mathrm{A} \stackrel{\text { alc.KOH }}{\longrightarrow} \mathrm{B}\). The product \(\mathrm{B}\) in the above reaction sequence is (a) styrene (b) 1 -phenyl ethanol (c) 2 -phenyl ethanol (d) p-ethylphenol

Reaction of benzene with 1,2-dichloroethane in presence of anhydrous aluminium chloride will give

Phenol + phthalic anhydride \(\frac{\text { conc. } \mathrm{H}_{2} \mathrm{SO}_{4}}{\text { heat }}{\longrightarrow}(\mathrm{X})\). The product \((\mathrm{X})\) is used as (a) an antipyretic (b) a catalyst (c) an indicator (d) a laboratory reagent
See all solutions

Recommended explanations on Chemistry Textbooks

Chemical Analysis

Read Explanation

Organic Chemistry

Read Explanation

Physical Chemistry

Read Explanation

Making Measurements

Read Explanation

Chemical Reactions

Read Explanation

Ionic and Molecular Compounds

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free