Methods of Preparation of Amines Preparation and Properties

Methods of Preparation of Amines Preparation and Properties

By Alkyl Halides :

→ By ammonolysis (Hoffmann’s Method) : When conc. ammonia and alkyl halide is heated at 373 K in a sealed tube, then a mixture of primary, secondary, tertiary amines and quaternary ammonium salt are obtained.

Methods of Preparation of Amines Preparation and Properties

→ Carbon-halogen bond in alkyl and benzyl halides easily break by nucleophiles. Therefore this reaction is an example of nucleophilic substitution reaction (SN) which ammonia or amine molecule acts as a nucleophile due to the presence of lone pair on the nitrogen atom.

Methods of Preparation of Amines Preparation and Properties 1

The order of reactivity of halides with amines is as follows :

RI > RBr > RCl

The ammonium salt formed initially gives a primary amine on treatment with a strong base

Methods of Preparation of Amines Preparation and Properties 2

→ Ammonolysis has the disadvantages of yielding a mixture of primary, secondary, tertiary amines and quaternary ammonium salt. It is not convenient to separate the mixture in the laboratory.

→ However, primary amine is obtained as a major product by taking large quantity of ammonia and less quantity of alkyl halide.

Methods of Preparation of Amines Preparation and Properties

→ By Gabriel’s Phthalamide Reaction This method can be used for preparing only primary amines. Phthalamide is treated with alcoholic KOH to give potassium phthalamide which is treated with alkyl halide. The hydrolysis of N-alkyl phtha]amide with 20% HCl under pressure gives primary amines.

Methods of Preparation of Amines Preparation and Properties 3
Methods of Preparation of Amines Preparation and Properties 4

By reduction of Cyanide and Isocyanide :

→ Primary amine can be prepared from reduction of alkyl or aryl cyanide in the presence of reducing agent like H2 (Raney Ni), LiAlH4 or Na/C2H5OH

Methods of Preparation of Amines Preparation and Properties 5

→ Hydrogen cyanide is reduced to prepare methyl amine

Methods of Preparation of Amines Preparation and Properties 6

→ The reaction when takes place in the presence of alcohol and sodium, then the reaction is called Mendius reduction.

→ If reaction is done with isocyanide, secondary amine is formed.

Methods of Preparation of Amines Preparation and Properties 7

By Amides :

→ By reduction : Amides are reduced to the corresponding amines containing same number of carbon atoms by LiAlH4 or Na/C2H5OH.

Methods of Preparation of Amines Preparation and Properties 8

→ By Hottmann’s Bromamide Reaction : Hoffmann developed a method for preparation of primary amines in which amides are treated with Bi and aqueous or ethanolic solution of NaOH. This reaction involves the migration of alkyl or aryl group from carbonyl carbon ofamide to the carbonyl atom of amine. The amine formed in such reaction contains one carbon atom less than the amide.

Methods of Preparation of Amines Preparation and Properties 9

By Reductive Ammination of Carbonyl Compounds :

→ Reaction between carbonyl compounds and ammonia results in the formation of irnines which are hydrogenated in the presence of Ni to give primary amine.

Methods of Preparation of Amines Preparation and Properties 10
Methods of Preparation of Amines Preparation and Properties 11

By Grlgnanrd’s reagent :

→ The reaction of grignard reagent with chioramine gives primary amines

RMgX + Cl — NH2 → RNH2 + MgXCl
CH3MgCl + Cl — NH2 → CH3NH2 + MgCl2

Methods of Preparation of Amines Preparation and Properties

By Acid Chloride (Curtius reaction) :

→ By this method, primary amines are formed by acid chlorides

Methods of Preparation of Amines Preparation and Properties 12

→ The reaction in which nitrogen is released from acetyl azide and hydrolysis of formed ijitermediate in acidic or basic medium form primary amine which contain one carbon less is called Curtius reaction.

By Carboxylic acid (Schmidi’s reaction) :

→ It is a modification of Curtius reaction. In this process carboxylic acid i heated with hydrazoic acid and cone. sulphuric acid to give primary amine.

Methods of Preparation of Amines Preparation and Properties 13

→ In this reaction aceylazide (R—CON3) and alkyl isocyanat (R—NCO) formed as intermediate compound.

By Nitroalkanes :

→ Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum at normal temperature.

Methods of Preparation of Amines Preparation and Properties 14
Methods of Preparation of Amines Preparation and Properties 15

→ Reduction of nitro compounds can be done with metals in acidic medium.
Example : Zn + HCl, Sn + HCl or Fe + HCl etc.

By reduction of Oximes :

→ Oximes obtained from aldehvdes and ketones by reaction with hydroxylamine can be reduced to primary amines with either Na/C2H5OH or LiAlH4.

From Aldehyde :

Methods of Preparation of Amines Preparation and Properties 16

From Ketone :

Methods of Preparation of Amines Preparation and Properties 17

Chemistry Notes

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