Revision: Std XII >> Alcohols, Phenols, and Ethers MAH-MHT CET (PCM/PCB) Alcohols, Phenols, and Ethers

Definition: Esterification

Alcohols and phenols form esters by reaction with carboxylic acid, acid halides and acid anhydrides. This reaction is called esterification.

Key Points: Alcohols, Phenols and Ethers

Alcohols and phenols both contain —OH group but differ in the type of hydrocarbon — aliphatic vs aromatic.
Ethers have the general formula R—O—R, where oxygen bridges two carbon groups.

Types of Alcohols

Type	Meaning	Position of —OH
Allylic Alcohol	—OH attached to sp³-hybridised carbon next to C=C double bond	Carbon next to C=C
Benzylic Alcohol	—OH attached to sp³-hybridised carbon next to aromatic ring	Benzylic carbon
Vinylic Alcohol	—OH attached directly to a vinylic carbon (CH₂=CH—) or aryl carbon	On C=C bond

Key Points: Classification of Alcohols, Phenols and Ethers

Classification of Alcohols

Based on number of —OH groups

Based on hybridisation of carbon bearing —OH (Monohydric only):

Type	Description	Example
Primary (1°)	—OH on primary carbon	R–CH₂–OH
Secondary (2°)	—OH on secondary carbon	R–CH(OH)–R
Tertiary (3°)	—OH on tertiary carbon	R–C(OH)(R)–R
Allylic	—OH on sp³ carbon next to C=C	CH₂=CH–CH₂OH
Vinylic	—OH directly on sp² carbon of C=C	CH₂=CH–OH
Benzylic	—OH on sp³ carbon next to aromatic ring	C₆H₅–CH₂–OH

Classification of Phenols

Type	—OH Groups	Example
Monohydric	1	Phenol
Dihydric	2	Catechol (Benzene-1,2-diol)
Trihydric	3	Phloroglucinol (Benzene-1,3,5-triol)

Classification of Ethers

Type	Description	Example
Simple / Symmetrical	Same alkyl/aryl groups on both sides of O	CH₃–O–CH₃ (Dimethyl ether), C₆H₅–O–C₆H₅ (Diphenyl ether)
Mixed / Unsymmetrical	Different alkyl/aryl groups on both sides of O	CH₃–O–C₂H₅ (Ethyl methyl ether), C₂H₅–O–C₆H₅ (Ethyl phenyl ether)

Key Points: Nomenclature of Alcohols, Phenols and Ethers

Alcohol names are derived from alkanes by replacing ‘e’ with ‘ol’ (e.g., methane → methanol).
In alcohols, the longest chain containing –OH is selected and numbered to give the lowest locant to the –OH group.
Phenol is the simplest aromatic alcohol; substituted phenols use ortho (1,2), meta (1,3), and para (1,4) positions.
Ethers are named as alkoxyalkanes in IUPAC; the smaller group becomes the alkoxy prefix.
Common names: Alcohol → alkyl + alcohol, Ether → alkyl groups + ether

Key Points: Preparation of Alcohols and Phenols

Hydroboration–Oxidation — This method of preparing alcohols from alkenes follows Anti-Markovnikov's rule; though the product seems as Markovnikov's, it is equivalent to anti-Markovnikov's addition.
Lucas Reagent Test — On adding Lucas reagent: a primary alcohol turns turbid only on heating, a secondary alcohol turns turbid slowly without heating, and a tertiary alcohol turns turbid immediately without heating.
Grignard Reagent Preparation of Alcohols — Formaldehyde (HCHO) + RMgX → 1° alcohol (R–CH₂OH); aldehyde (R'CHO) + RMgX → 2° alcohol; ketone (R'COR'') + RMgX → 3° alcohol.
Preparation of Phenol — Phenol can be prepared from chlorobenzene (NaOH/623 K/150 atm – Dow Process), benzene sulphonic acid (NaOH/573 K), cumene (O₂/cobalt naphthenate/423 K – commercial method), and aniline (NaNO₂–HCl/273 K, then H₂O/Δ – diazotisation).
Acidic Character — In aqueous medium, phenols show a weak acidic character, while alcohols are neutral.

Key Points: Physical Properties of Alcohols and Phenols

Intermolecular Forces — Alcohols and phenols are polar; –OH groups form strong hydrogen bonding.
Boiling Point — Increases with molecular mass; decreases with branching (n-butyl > isobutyl > sec-butyl > tert-butyl).
Solubility — Phenols and lower alcohols (≤3 C) are water-soluble via H-bonding with water.
Kolbe's & Reimer–Tiemann — Phenoxide + CO₂/H⁺ → salicylic acid; + CHCl₃/NaOH → salicylaldehyde (electrophile: CCl₂).
Oxidation/Reduction of Phenol — Na₂Cr₂O₇/H₂SO₄ → p-benzoquinone; 3H₂/Ni/433 K → cyclohexanol; Zn → benzene.

Key Points: Chemical Properties of Alcohols and Phenols

Litmus Test — Aqueous alcohols are neutral to litmus, while aqueous phenols turn blue litmus red, confirming the acidic character of phenols.
Reaction with Bases — Phenols react with NaOH to form water-soluble sodium phenoxide (regenerated on acidification with HCl) but do not react with NaHCO₃, since phenol is a weak acid.
Esterification — Alcohols/phenols react with carboxylic acids (conc. H₂SO₄ catalyst), acid anhydrides (H⁺ catalyst), or acid chlorides (in pyridine) to form esters; Aspirin is the acetyl derivative of salicylic acid formed using acetic anhydride.
Reactivity with Hydrogen Halides — Order of alcohol reactivity: 3° > 2° > 1°; order of HX reactivity: HI > HBr > HCl (HCl needs anhydrous ZnCl₂ catalyst).
Oxidation of Alcohols — 1° alcohol → aldehyde (with PCC, best reagent) → further to carboxylic acid (with KMnO₄/K₂Cr₂O₇/HNO₃); 2° alcohol → ketone (with CrO₃); 3° alcohols resist oxidation and break C–C bonds only at high temperature.

Key Points: Physical Properties of Ethers

Methods of preparation of ethers: Acid-catalysed dehydration of alcohols (conc. H₂SO₄, 443 K); catalytic dehydration (Al₂O₃, 250°C); Williamson synthesis (alkyl halide + sodium alkoxide, Sₙ2); reaction of alkyl halides with dry Ag₂O.
Preparation of Diethyl Ether (Simple Ether): From ethanol using conc. H₂SO₄ / H₃PO₄ at 413 K; or by Williamson's synthesis from C₂H₅ONa + BrCH₂CH₃ under heat.
Reactions of Diethyl Ether: O₂ (long contact) → peroxide; dil. H₂SO₄ → 2 C₂H₅OH; PCl₅ → C₂H₅OH + C₂H₅Cl; hot HI → C₂H₅I + C₂H₅OH; excess HI → 2 C₂H₅I.
Preparation of Anisole (Mixed Ether): CH₃Br + sodium phenoxide (C₆H₅ONa) → Methyl phenyl ether (Anisole) on heating.
Reactions of Anisole: HI (398 K) → phenol + CH₃I; Br₂/CH₃COOH → p-bromoanisole (major) + o-bromoanisole (minor); conc. HNO₃ + conc. H₂SO₄ → 4-nitroanisole (major) + 2-nitroanisole (minor); CH₃Cl/AlCl₃ → 4-methoxytoluene (major) + 2-methoxytoluene (minor); CH₃COCl/AlCl₃ → 4-methoxyacetophenone (major) + 2-methoxyacetophenone (minor).

Key Points: Chemical Properties of Ethers

1. Classification: Chemical properties of ethers are classified mainly into reactions involving cleavage of the C–O bond.

2. C–O Bond Cleavage Reactions:

3. Reactivity order of HX with ethers: HI > HBr > HCl.

4. Preparation of Diethyl Ether:

5. Reactions of Diethyl Ether: