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AMINES

Organic Chemistry

Class XII

Dr. Tanuja Nautiyal

Amines Amines are similar to ammonia (base) with one

or more alkyl groups bonded to the nitrogen atom.

Amines occurs widely in living organisms. Many amines are naturally occurring

compounds that are very active physiologically. Numerous drugs used for the treatment of

mental illness, hay fever, heart problems, and other physical disorders are amines.

Bonding Characteristics of Nitrogen Atoms in Organic Compounds:

Carbon forms four bonds. (4 valence electron, 4 covalent bond, No nonbonding electron pair).

Nitrogen forms three bonds(5 valence electron, 3 covalent bond,1 nonbonding electron pair).

An Amine is an organic derivative of ammonia(NH4) in which one or more alkyl, cycloalkyl, oraryl groups are attached to the nitrogen atom.

Alkyl amine

Aryl amine

Amines are classified on the basis of how manyhydrocarbon groups are bonded to theammonia nitrogen atom as:

Primary amines (10) Secondary amines (20)Tertiary amines (30)

Classification of Amines

Primary Amine is an amine in which the nitrogen atom isbonded to one hydrocarbon group and two hydrogenatoms.The generalized formula for a primary amine is RNH2.The functional group present in a primary amine, the NH2

group is called an Amino group.An Amino group is the -NH2 functional group.

Classification of Amines

Primary Amine

CH3 – NH2

Secondary Amine Is an amine in which the nitrogenatom is bonded to two hydrocarbon groups and onehydrogen atom. The generalized formula for asecondary amine is R2NH. CH3 – NH – CH3

Secondary Amine

Classification of Amines

Tertiary Amine is an amine in which the nitrogenatom is bonded to three hydrocarbon groups andno hydrogen atom. The generalized formula for atertiary amine is R3N

Tertiary Amine

Classification of Amines

Classification of Amines

The methylamines (mono-, di-, tri-) and ethylamine are gases at room temperature , other amines are liquid at room temperature.

Amines are irritating to the skin, eyes, and mucous membranes and are toxic by ingestion.

Aromatic amines are generally toxic. Amines are readily absorbed through the skin and affect both the blood and the nervous system.

Physical Properties of Amines:

The boiling points of amines are intermediatebetween those of alkanes and alcohols of similarmolecular mass.

Amines are higher than alkane boiling point, becausehydrogen bonding is possible between aminemolecules but not between alkane molecules.Intermolecular hydrogen bonding of amines involvesthe hydrogen atoms and nitrogen atoms of the aminogroup.

Boiling points of amines

Tertiary amines have lower boiling point thanprimary and secondary amines becauseintermolecular hydrogen bonding is not possible intertiary amines.Secondary and tertiary amines have no hydrogenatoms directly bonded to the nitrogen atom.

Boiling points of amines

Tertiary Amines

Primary Amines

Secondary Amines

Boiling point Increases

The boiling point of amines are lower than those ofcorresponding alcohols, because N – H bonds are weakerthan O – H bonds, as nitrogen is less electronegative thanoxygen.The difference in hydrogen-bond strength :O– H electronegativity differences (3.5) -(2.1) = 1.4N– H electronegativity differences(3.0) - (2.1) = 0.9

Why the boiling point of amines are lower than those of corresponding alcohols?

Amines with less than six carbon atoms are infinitelysoluble in water.

This solubility results from hydrogen bonding betweenthe amines and water as amine nitrogen atom has anonbonding electron pair that can form a hydrogenbond with a hydrogen atom of water.

Solubility of Amines

Basicity of Amines

Both amines and ammoniaproduce basic aqueous solution

Amines and Ammonia are weak bases. The weak-base behaviour of amines and ammonia are due to its acceptance of a proton (H+) from water to produce ammonium ion and hydroxyl ion.

Both amines and ammonia produce basic aqueous solution

Basicity of Amines

NH3 + H2O → NH4+ + OH-

Ammonia Ammonium ion

CH3NH2 + H2O → CH3NH3+ + OH-

Methylamine Methyl ammonium ion

Nomenclature of Amines

Nomenclature of Amines

Naming the positive ion that results from theinteraction of an amine with water is based on thefollowing two rules:

Rule 1: For alkylamine, the ending of the name of theamine is changed from amine to ammonium ionExamples: Ethylammonium ion

Rule 2: For aromatic amines, the final –e of the name ofthe amine is replaced by –iumionExamples: Anilinium ion

Nomenclature of Amines

Preparation of Amines

Reduction of nitro compounds

Aromatic amines are normally prepared by reduction of the corresponding aromatic nitro compound.

Aniline is prepared from nitrobenzene. Reducing agents: Fe/H+, Sn/H+ or catalytic hydrogenation (example, H2/Pdor Pt or Ni).

Reduction of amides

Amides yield primary amines on reduction by lithiumaluminum hydride, LiAlH4. The oxygen atom isreplaced by two hydrogen atoms, 2o and 3o amidesproduce 2o and 3o amines, respectively.

Reduction of Nitriles

Nitriles can be reduced by strong reducing agent like H2

with catalyst (Ni) or LiAlH4 to yield primary amines.

Hoffmann degradation of amides

Hoffmann degradation of amides Heating the amideswith a mixture of bromine and KOH or NaOH. amideswill change to amines. is used to shorten the chain byone carbon.

The reaction of ammonia with an alkyl halide leads tothe formation of a primary amine.

The primary amine that is formed can also react withthe alkyl halide, which leads to a di-substitutedamine.(2o amine)

Reduction of halides with ammonia

Chemical Reactions of Amines

Reaction of amines with an acid gives aquarternary salts (an ammonium ion)

Alkylation of amines

Reaction of Amines

Formation of amides

From acid anhydride

From acid chloride

From esters

Reaction with nitrous acid

Primary aliphatic and aromatic amines formalkyldiazonium salts with nitrous acid.

We get many useful products from alkyldiazonium salts,as it is an unstable salt.

Reaction with nitrous acid

Primary amines

Secondary amines

Ternary amines

Reaction of nitrous acid with aliphatic amines in coldacidic solution can be used to distinguish betweenprimary, secondary and tertiary amines.

Reaction of nitrous acid with amines

Reaction with nitrous acid

Secondary aliphatic and aromatic amines formnitrosoamine (yellow oils) with nitrous acid.

Primary amines heated with tri-chloromethane and alcoholic KOH solution will produce a foul odour of isocyanide RNC

Carbyl amine Reaction

Conversion of Primary, Secondary & Tertiary Amines

Presentation by

Dr. Tanuja NautiyalSharda Public School

Almora