Introduction to Alcohols, Phenols & Ethers
Hydroxy compounds have -OH group attached to aliphatic or aromatic carbon. Alcohols are classified as monohydric, dihydric, trihydric based on number of -OH groups.
Alcohols: R-OH; Phenols: Ar-OH; Ethers: R-O-R'.
Classification of Alcohols
Monohydric (1°/2°/3°), Dihydric (Glycols), Trihydric (Glycerol).
Preparation of Monohydric Alcohols
From Alkyl Halides
1° halides give good yield; 3° give alkenes.
From Alkenes
From Carbonyl Compounds
| Compound | Reagent | Product |
|---|---|---|
| Aldehyde (RCHO) | LiAlH4 or H2/Pd | 1° Alcohol (RCH2OH) |
| Ketone (RCOR') | NaBH4 or LiAlH4 | 2° Alcohol (RCH(OH)R') |
| Carboxylic Acid (RCOOH) | LiAlH4 | 1° Alcohol (RCH2OH) |
| Ester (RCOOR') | LiAlH4 | RCH2OH + R'OH |
From Grignard Reagents
Industrial Methods
Oxo Process: Alkene + CO + H2 → Aldehyde → Alcohol
Physical Properties of Alcohols
Chemical Properties of Alcohols
Acidity & O-H Cleavage
Alcohols weak acids: ROH + Na → RONa + 1/2H2
Acidity: 1° > 2° > 3°
Esterification: ROH + R'COOH → R'COOR + H2O
C-O Cleavage
Dehydration
Oxidation
| Alcohol Type | Product | Reagent |
|---|---|---|
| 1° | Aldehyde/Carboxylic Acid | PCC/K2Cr2O7 |
| 2° | Ketone | K2Cr2O7 |
| 3° | No Reaction | - |
Distinction Tests
| Test | 1° | 2° | 3° |
|---|---|---|---|
| Lucas (ZnCl2/HCl) | No Rx/Heat | 5 min | Immediate |
| Victor Meyer | Red | Blue | No Colour |
| Iodoform | CH3CH(OH)R | CH3COR | CH3C(OH)R2 |
Polyhydric Alcohols
Dihydric (Ethylene Glycol)
Preparation: From Ethylene, Dibromoethane
Properties: Colourless, viscous, antifreeze
Reactions: Esterification, Dehydration to Aldehydes
Trihydric (Glycerol)
Preparation: From Oils/Fats, Propene
Properties: Colourless, viscous, hygroscopic
Reactions: Nitration to Nitroglycerin, Oxidation
Uses: Explosives, Antifreeze, Soaps
Phenols
Preparation
Physical Properties
Colourless solid/liquid, characteristic smell, soluble in water due to H-bonding, higher BP than hydrocarbons.
Chemical Properties
Stronger acid than alcohols: Forms phenoxide
Electrophilic Substitution: Ortho/Para directing, Halogenation, Nitration, Reimer-Tiemann (CHO), Kolbe (COOH)
Other: Esterification, Ether formation, Oxidation to Quinone
Tests
FeCl3: Violet; Br2 water: White ppt; Liebermann: Green/Blue
Derivatives of Phenol
| Compound | Preparation | Properties/Uses |
|---|---|---|
| Picric Acid | Phenol + Conc HNO3 | Yellow explosive, dye |
| Catechol | From o-Phenolsulphonic Acid | Developer, Antioxidant |
| Resorcinol | From m-Benzenedisulphonic Acid | Antiseptic, Dyes |
| Hydroquinone | From p-Benzoquinone | Developer, Antioxidant |
Ethers
Preparation
Williamson: RX + R'ONa → ROR'
Dehydration: 2ROH → ROR + H2O (H2SO4, 140°C)
From Alkyl Halides + Ag2O
Physical Properties
Gases/Liquids, low BP, soluble in water like alcohols, dipole moment.
Chemical Properties
Peroxide Formation, Hydrolysis with HI/HBr, Halogenation
Ring Substitution in Aromatic Ethers (o/p directing)
Important Points for Exams
High Yield Concepts
- Preparation Methods: Grignard, Hydroboration (Anti-Markovnikov)
- Oxidation: 1° → Aldehyde/Acid, 2° → Ketone, 3° No Rx
- Dehydration: Saytzeff Rule, 3° > 2° > 1°
- Phenol Acidity & Reactions: Reimer-Tiemann, Kolbe
- Ethers: Williamson Synthesis, Cleavage with HI
- Distinction Tests: Lucas, Iodoform, Victor Meyer
JEE Main Weightage
Typically 3-5 questions from this chapter. Focus on mechanisms, tests, preparations.