(i) Kolbe’sreaction:
When phenol is treated with sodium hydroxide, sodiumphenoxide is produced. This sodium phenoxide when treated with carbon dioxide,followed by acidification, undergoes electrophilic substitution to giveortho-hydroxybenzoic acid as the main product. This reaction is known asKolbe’s reaction.
(ii) Reimer-Tiemannreaction:
When phenol is treated with chloroform (CHCl3) inthe presence of sodium hydroxide, a −CHO group is introduced at the orthoposition of the benzene ring.
This reaction is known as the Reimer-Tiemann reaction.
The intermediate is hydrolyzed in the presence of alkalisto produce salicyclaldehyde.
(iii) Williamsonether synthesis:
Williamson ether synthesis is a laboratory method toprepare symmetrical and unsymmetrical ethers by allowing alkyl halides to reactwith sodium alkoxides.
This reaction involves SN2attack of the alkoxide ion on the alkyl halide. Better results are obtained incase of primary alkyl halides.
If the alkyl halide is secondary or tertiary, thenelimination competes over substitution.
(iv) Unsymmetricalether:
An unsymmetrical ether is an ether where twogroups on the two sides of an oxygen atom differ (i.e., have an unequal numberof carbon atoms). For example: ethyl methyl ether (CH3−O−CH2CH3).