Question

Give reasons of the following observations:

a. Aniline is acetylated before nitration reaction.

b. pK_b of aniline is lower than the m-nitroaniline.

c. Primary amine on treatment with benzenesulphonyl chloride forms a product which is soluble in NaOH however secondary amine gives product which is insoluble in NaOH.

d. Aniline does not react with methyl chloride in the presence of anhydrous AlCl₃ catalyst.

Answer 1

a. Aniline is acetylated, before nitration reaction in order to avoid formation of tarry oxidation products and protecting the amino group, so that p -nitro derivative can be obtained as major product.

b. pK_b of aniline is lower than the m-nitro aniline. The basic strength of aniline is more that m-nitroaniline. pk_b value is inversely proportional to basic strength. Presence of Electron withdrawing group decrease basic strength.

c. Due to the presence of acidic hydrogen in the N-alkylbenzenesulphonamide formed by the treatment of primary amines.

d. Aniline does not react with methylchloride in the presence of AlCl₃ catalyst , because aniline is a base and AlCl₃ is Lewis acid which lead to formation of salt.