Alcohols, Phenols & Ethers 

Alcohols – Introduction

Alcohols are derivatives of water in which one hydrogen atom is replaced by an alkyl group. General formula: R–OH

• –OH group is directly attached to an aliphatic carbon
• Simplest alcohol: Methanol (CH₃OH)

Preparation of Alcohols

From Alkenes (Hydration)

• Acid-catalysed hydration (H₂SO₄): follows Markovnikov’s rule; rearrangement possible
• Oxymercuration–demercuration: Markovnikov addition without rearrangement
• Hydroboration–oxidation: anti-Markovnikov addition

Reduction Methods

• Aldehydes → 1° alcohols
• Ketones → 2° alcohols
• Carboxylic acids, acid chlorides → alcohols (LiAlH₄)
• NaBH₄ reduces aldehydes, ketones and acid halides only

From Grignard Reagents (RMgX)

• HCHO + RMgX → 1° alcohol
• Aldehyde + RMgX → 2° alcohol
• Ketone + RMgX → 3° alcohol
• Ester + 2RMgX → 3° alcohol

Commercial Preparation

• Methanol: CO + 2H₂ → CH₃OH (Cu–ZnO–Cr₂O₃)
• Ethanol: Fermentation of sugars

Physical Properties of Alcohols

• Higher boiling point than haloalkanes (H-bonding)
• Boiling point decreases with branching
• Lower alcohols are completely miscible with water

Acidity of Alcohols

• Alcohols are weaker acids than water
• Acidic strength: 1° > 2° > 3° alcohol
• More +I groups → less acidic

Reactions of Alcohols

Cleavage of O–H Bond

• With Na → sodium alkoxide + H₂
• With RMgX → alkane

Cleavage of C–O Bond

• With PCl₅, PCl₃, SOCl₂ → alkyl halides
• Reactivity: 3° > 2° > 1° alcohol

Lucas Test

• 3° alcohol: immediate turbidity
• 2° alcohol: turbidity in 5–10 min
• 1° alcohol: no turbidity at room temp

Dehydration (conc. H₂SO₄)

• At 140°C → ether
• At 170°C → alkene
• Ease: 3° > 2° > 1° alcohol

Oxidation

• 1° alcohol → aldehyde → acid
• 2° alcohol → ketone
• 3° alcohol → no oxidation

Polyhydric Alcohols

Ethylene Glycol (Ethane-1,2-diol)

• Colourless, viscous liquid
• Used as antifreeze
• High boiling point (extensive H-bonding)

Glycerol (Propane-1,2,3-triol)

• Prepared by saponification of fats/oils
• Highly viscous, hygroscopic liquid
• Used in explosives (nitroglycerine), cosmetics, medicines

Phenols

Phenols have –OH group directly attached to an aromatic ring.

Acidity of Phenols

• More acidic than alcohols
• EWG increases acidity; EDG decreases acidity
• p-nitrophenol > o-nitrophenol > m-nitrophenol

Preparation of Phenol

• From benzene sulphonate (fusion with NaOH)
• From chlorobenzene (Dow’s process)
• From diazonium salts
• Cumene–phenol process (industrial)

Reactions of Phenol

• Electrophilic substitution (o,p-directing)
• Nitration → picric acid
• Kolbe reaction → salicylic acid
• Reimer–Tiemann reaction → salicylaldehyde

Ethers

Ethers are derivatives of water in which both hydrogens are replaced by alkyl/aryl groups.

Preparation

• Dehydration of 1° alcohols
• Williamson ether synthesis (SN2)

Properties

• Lower boiling point than alcohols
• Polar but no hydrogen bonding
• Lower ethers are soluble in water

Reactions of Ethers

• With HI: cleavage of C–O bond
• Reactivity: HI > HBr > HCl
• Aromatic ethers undergo electrophilic substitution (o,p-directing)