alkyl halide followed by alkaline hydrolysis gives primary amine. Aniline cannot be prepared by this method because the arylhalides do not undergo nucleophilic substitution with the anion formed by phthalimide NH alcoholic NK R - X (SN2) R aqueous KOH OK OK + R NH ( amine) Phthalimide Potassium phthalimide N - alkyl phthalimide KOH –H O Potassium pthalati b) Hoffmann’s ammonolysis When Alkyl halides (or) benzylhalides are heated with alcoholic ammonia in a sealed tube, mixtures of , and amines and quaternary ammonium salts are obtained. CH Br NH .. NH ..
CH - Br (CH )NH .. CH Br (CH ) N .. CH Br (CH ) N Br - amine - amine - amine Quarternary ammonium bromide This is a nucleophilic substitution , the halide ion of alkyl halide is substituted by the -NH group. The product primary amine so formed can also has a tendency to act as a nucleophile and hence if excess alkyl halide is taken, further nucleophilic substitution takes place leading XII U13-Organic Nitrogen XII U13-Organic Nitrogen - - - - to the formation of quarternary ammonium salt.
However, if the process is carried out with excess ammonia, primary amine is obtained as the major product. The order of reactivity of alkylhalides with amines. RI > RBr > RCl c) Alkyl halide can also be converted to primary amine by treating it with sodium azide (NaN ) followed by the reduction using lithium aluminium hydride. Br NaN N LiAlH NH + N Methylbromide Methyl azide Methylamine d) Preparation of aniline from chlorobenzene When chlorobenzene is heated with alcoholic ammonia, aniline is obtained.
C H Cl NH Cu O / C NH aniline ) Ammonolysis of hydroxyl compounds a) when vapour of an alcohol and ammonia are passed over alumina, W O (or) silica at C,