Name Reactions - Alcohols, Phenols and Ethers
(a) Kolbe’s reaction: When sodium phenoxide is heated with CO2 at 400 K under a pressure of 4 –7 atm, the resulting product on acidification yields salicylic acid.
Salicylic acid is the starting material for the manufacture of 2-acetoxybenzoic acid (aspirin).
(b) Reimer–Tiemann reaction: Treatment of phenol with chloroform in the presence of sodium hydroxide followed by hydrolysis of resulting product gives o-hydroxybenzaldehyde (salicylaldehyde) as a major product.
(c) Williamson synthesis: It consists of reacting an alkyl halide with sodium alkoxide or sodium phenoxide to form ether.
It is a convenient method for the preparation of symmetrical as well as unsymmetrical ethers.
DISTINCTION BETWEEN PRIMARY, SECONDARY AND TERTIARY ALCOHOLS
(a) Lucas test: In this test, the alcohol is treated with Lucas reagent which is an equimolar mixture of HCl and ZnCl2. Alcohols are soluble in Lucas reagent and form a clear solution. On reaction, alkyl chlorides are formed which being insoluble result in turbidity in the solution.
If turbidity appears immediately, tertiary alcohol is indicated. If turbidity appears within five minutes, secondary alcohol is indicated. If turbidity appears only upon heating, primary alcohol is indicated.
(b) Iodoform test: When ethyl alcohol or any alcohol containing the group CH3—CH(OH)— or CH3—CO— group is heated with iodine and aqueous NaOH or Na2CO3 solution at 333–343 K, a yellow precipitate of iodoform is obtained.
(c) Ferric chloride test for phenols: Phenol gives a violet-coloured water soluble complex with ferric chloride.
In general, all compounds containing enolic group (=C—OH) respond to this test. However, the colours of complexes are different such as green, blue, violet, etc., and depend upon the structure of phenols.
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