There are various methods by which amines are prepared. So the following methods are :

`=>` Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum and also by reduction with metals in acidic medium.

`=>` Nitroalkanes can also be similarly reduced to the corresponding alkanamines.

`=>` Reduction with iron scrap and hydrochloric acid is preferred because `color{red}(FeCl_2)` formed gets hydrolysed to release hydrochloric acid during the reaction. Thus, only a small amount of hydrochloric acid is required to initiate the reaction.

The carbon - halogen bond in alkyl or benzyl halides can be easily cleaved by a nucleophile.

● Hence, an alkyl or benzyl halide on reaction with an ethanolic solution of ammonia undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (`color{red}(–NH_2)`) group.

● This process of cleavage of the `color{red}(C–X)` bond by ammonia molecule is known as ammonolysis.

● The reaction is carried out in a sealed tube at `373 K`.

● The primary amine thus obtained behaves as a nucleophile and can further react with alkyl halide to form secondary and tertiary amines, and finally quaternary ammonium salt. See fig.

`color{red}(underset(1^o)(RNH_2) overset(RX)→ underset(2^o)(R_2NH) overset(RX)→ underset(3^o)(R_3N) overset(RX)→ undersettext(Quaternary ammonium salt)(R_4 overset(+)N overset(-)X))`

`=>` The free amine can be obtained from the ammonium salt by treatment with a strong base :

`color{red}(R - overset(+)NH_3overset(-)X+NaOH → R-NH_2+H_2O +overset(+)Na overset(-)X)`

`color{green}(text(Disadvantage ))` : Ammonolysis yields a mixture of primary, secondary and tertiary amines and also a quaternary ammonium salt.

● However, primary amine is obtained as a major product by taking large excess of ammonia.

● The order of reactivity of halides with amines is `color{red}(RI > RBr > RCl)`.

`=>` Nitriles on reduction with lithium aluminium hydride `color{red}(LiAlH_4)` or catalytic hydrogenation produce primary amines.

● This reaction is used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine.

`color{red}(R-C equiv N underset(Na(Hg)//C_2H_5OH) overset(H_2//Ni)→ R- CH_2-NH_2)`

The amides on reduction with lithium aluminium hydride yield amines.

`color{red}(R - overset(overset(O)(||))C-NH_2 underset((ii)H_2O) overset((i) LiAlH_4)→ R-CH_2-NH_2)`

`=>` Gabriel synthesis is used for the preparation of primary amines.

`=>` Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine.

`=>` Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

`=>` Hoffmann developed a method for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide.

`=>` In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom.

`=>` The amine so formed contains one carbon less than that present in the amide.

`color{red}(R - overset(overset(O)(||))C-NH_2+Br+4NaOH → R-NH_2+Na_2CO_3+2NaBr+2H_2O)`