Explain the following with an example:
i. Kolbe's reaction
ii. Reimer-Tiemann reaction
iii. Williamon's ether synthesis
iv. Usymmetrical ether

Explanation

(i) Kolbe's reaction : Sodium phenoxide when heated with `CO_(2)` at 400K under a pressure of 4-7 atmospheres followed by acidification gives 2-hydroxybenzoic acid (salicylic acid) as the major product along with a small amount of 4-hydroxybenzoic acid. This reaction is called Kolbe's reaction.

(ii) Reimer-Tiemann reaction : Treatment of phenol with CHC 13 in presence of aqueous sodium or potassium hydroxide at 340 K followed by hydrolysis of the resulting product gives 2-hydroxybenzaldehyde (salicyialdehyde) as the major product. This reaction is called Reimer - Tiemann reaction.

(iii) Williamson's ether synthesis : It involves the treatment of an alkyl halide with a suitable sodium alkoxide to obtain ethers. The sodium alkoxide for the purpose is prepared by action of sodium on a suitable alcohol. In this reaction alkyl halide should primary. Secondary and tertiary halides will predominantly give an alkene.
`underset("Sodium ethoxide")(CH_(3)CH_(2)-bar(O)-Na^(+))+Br-underset("Ethylbromide")(CH_(2)CH_(3))overset(330K)underset(S_(N)2)rarr underset("Diethylether")(CH_(3)CH_(2)-O-CH_(2)CH_(3))+Na^(+)Br^(-)`
(iv) Unsymmetrical ether : If the alkyl or aryl groups attached to the oxygen atom are different, enthers are called unsymmetrical ethers. For example, ethylmethylether, 4-chlorophenyl-4- nitrophenyl ether, ect.