CHAPTER AT A GLANCE
1. Alcohols and phenols may be classified as monohydric, dihydric, trihydric or polyhydric according to number of hydroxyl groups they contain one, two, three or many respectively in their molecules.
2. Primary (1°), secondary (2°) and tertiary (3°) alcohols are those in which OH group is attached to a primary, secondary and tertiary carbon atom respectively.
3. Ethers are classified as simple or symmetrical ethers if the alkyl or aryl groups attached to the oxygen atom are same, and mixed or unsymmetrical ethers if the two groups are different.
4. Preparation of Alcohols
(i) From alkenes:
- (a) By acid catalysed hydration: The addition reaction takes place in accordance with Markovnikov’s rule.
- (b) By hydroboration-oxidation: Hydration of alkenes by this method takes place in anti-markovnikov’s way.
- (c) By mercuration demercuration.
(ii) From carbonyl compounds
- (a) By reduction of aldehydes and ketones : On reduction aldehydes give l O alcohols and ketones give 2° alcohols.
- (b) By reduction of carboxylic acids and esters
- (c) From Grignard reagents
5. Phenols may be prepared by
(i) Substitution of halogen in
(a) Haloarenes
(b) Sulphonic acids, e.g., in benzenesulphonic acid
(ii) From hydrolysis of diazonium salts (iii) Industrially from Cumene
6. Chemical reactions of alcohols
(i) Reactions involving the cleavage of the O – H bond:
(a) Reaction with alkali metals- acidic nature:
7. Reactions of phenols –
(i) Phenols are weak acids: They turn blue litmus solution to red but do not decompose weak alkali like NaHCO3 (difference from carboxylic acids).
(ii) Electrophilic substitution reactions : The presence of -OH group in phenols activates the aromatic ring towards electrophilic substitution and directs the incoming group to the ortho and para positions due to resonance effect.
(iii) Kolbe’s reaction : In this reaction sodium phenoxide is treated with CO2 at 400K under 3 – 7 atm pressure, sodium salicylate is formed which is
acidified to get salicylic acid.
(iv) Reimer-Tiemann reaction: In this reaction phenol reacts with chloroform in presence of NaOH and produce salicylaldehyde or with CC14 and NaOH to give salicylic acid.
8. Preparation of Ethers:
9. Physical Properties :
(i) Boiling point of ethers are much lower than corresponding alcohols, because ethers do not form intermolecular H-bonding.
(ii) Insoluble in water.
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