Phenols and Ethers — Part 1: Phenols: visual lesson, ISC Class 12 Chemistry

Lesson

Phenols

Part 1 — compounds with an –OH group directly on a benzene ring.

In this lesson you will

Classify and name phenols and write equations for preparing phenol by four methods
Explain why phenol is more acidic than ethanol, and write its reactions with NaOH, Na, Zn, acetyl chloride, acetic anhydride and PCl₅
Predict products of electrophilic substitution, Kolbe and Reimer–Tiemann reactions
Describe the ferric chloride and azo dye tests and uses of phenol

Table of phenols and their uses
Phenol	Where it is used
Phenol (carbolic acid)	First surgical antiseptic; Bakelite; drugs
Salicylic acid (from phenol)	Aspirin, skin creams
4-Chloro-3,5-dimethylphenol	Household disinfectants
Picric acid	Dyes; formerly explosives

Concept

Classification and nomenclature

Phenols are monohydric, dihydric or trihydric by the number of –OH groups on the ring. Substituted phenols are named as derivatives of phenol, numbering from the C–OH carbon.

Table of names of phenols
Structure	Common name	IUPAC name
C₆H₅OH	Phenol (carbolic acid)	Phenol
CH₃C₆H₄OH (meta)	m-Cresol	3-Methylphenol
C₆H₄(OH)₂ (1,2)	Catechol	Benzene-1,2-diol
C₆H₄(OH)₂ (1,3)	Resorcinol	Benzene-1,3-diol
C₆H₄(OH)₂ (1,4)	Quinol (hydroquinone)	Benzene-1,4-diol
C₆H₃(OH)₃ (1,2,3)	Pyrogallol	Benzene-1,2,3-triol

Concept

Preparation of phenol

Four methods: (1) from benzenediazonium chloride (warm with water); (2) from chlorobenzene (Dow process: NaOH, 623 K, 300 atm); (3) from benzenesulphonic acid (sodium salt fused with NaOH, then acid); (4) from cumene (industrial).

\ce{C6H5N2Cl + H2O ->[warm] C6H5OH + N2 + HCl}

\ce{C6H5Cl + 2NaOH ->[623 K, 300 atm] C6H5ONa + NaCl + H2O}

\ce{C6H5SO3Na + 2NaOH ->[573 K] C6H5ONa + Na2SO3 + H2O}

Table of methods of preparing phenol
Starting material	Key reagent and condition
Benzenediazonium chloride	Warm with water
Chlorobenzene	NaOH, 623 K, 300 atm; then HCl
Sodium benzenesulphonate	Fuse with NaOH; then HCl
Cumene	O₂ (air); then dilute acid

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