Amines, Amino Acids, Polymers

Chemistry Unit 4

Amines

Amines can be thought of as derivatives of ammonia.

Ammonia

It is where one or more of the hydrogen atoms have been replaced by alkyl or aryl groups.

Primary amine

Secondary amine

Tertiary amine

Naming amines – suffix –amine OR prefix amino-

Primary - general formula RNH₂

CH₃-NH₂ is methylamine

Benzene amine is amino benzene

Secondary – RR’NH

(CH₃)₂NH is dimethylamine

Tertiary – RR’R’’N

(C₂H₅)₃N is trimethylamine

And as always different substituents are written in alphabetical order

Reactivity

Amines have a lone pair of electrons.

This lone pair may be used to form a bond with a H⁺ ion, and we say the amine is acting as a base.

The lone pair may also be used to form a bond with an electron-deficient atom, and we say the amine is acting as a nucleophile.

Amines as a base

Amines can accept a proton à they are B.L. bases.

The lone pair on the nitrogen atom allows the nitrogen atom to act as a proton acceptor.

All amines react with strong acids to form alkylammonium salts.

Reactions with acids

Amines react with acids in the same way as ammonia:

            NH₃ + HCl à NH₄Cl

            2NH₃ + H₂SO₄ à (NH₄)₂SO₄

Primary amines:    R₁-NH₂ + HCl à R₁-NH₃Cl

                                    2R₁-NH₂ + H₂SO₄ à (R₁-NH₃)₂SO₄

Secondary amines: R₁R₂-NH + HCl à R₁R₂-NH₂Cl

                                    2R₁R₂-NH + H₂SO₄ à (R₁R₂-NH₂)₂SO₄

Tertiary amines:    R₁R₂R₃-N + HCl à R₁R₂R₃-NHCl

                                    2R₁R₂R₃-N + H₂SO₄ à (R₁R₂R₃-NH)₂SO₄

Comparison of base strengths

The basicity of an amine is dependent on the availability of the lone pair of electrons on the nitrogen atom. The more available the lone pair, the stronger the base. The availability of the lone pair in turn depends on how much electron density is on the nitrogen atom, and this depends on the adjacent atoms.

Alkyl groups release electrons away from the alkyl group and towards the nitrogen atom. (Inductive effect)

The inductive effect of the alkyl group increases the electron density on the nitrogen atom. Primary alkylamines are stronger bases than ammonia.

Secondary alkylamines have 2 inductive effects and are therefore stronger bases than primary alkylamines.

Tertiary alkylamines are not stronger bases than secondary alkylamines, as they are less soluble in water.

Aryl groups withdraw electrons from the nitrogen, because the lone pair of…