There can be a fourth aliphatic group bonded to the nitrogen, it is no longer an amine but it referred to as a quaternary ammonium ion. NH3 is also not an amine but is often used in comparisons along with its protonated molecule, NH4+, ammonium.

Phenylamines are used in the production of azo dyes, which are synthetic dyes used in food and textiles.

Physical Properties

Primary and secondary amines have hydrogen bonding so have relatively high melting points for their Mr, a tertiary amine does not have a hydrogen bonded to its nitrogen so does not hydrogen bonding so is lower melting point than primary and secondary. An ammonium ion produces electrostatic forces and has an ionic structure produces very high melting points.

Ammonia and shorter chain amines are polar enough to dissolve in water, amines with longer chain are less soluble in water as the chain length increases. Similar to the solubilities of carboxylic acids.

Ammonia and amines can act as Bronsted-Lowry bases and accept a proton, they can also act as nucleophiles as it has a lone pair.

Production of Amines

Reduction of RNO2 to RNH2 Sn/HCl

Nitro containing compounds can be reduced using tin and hydrochloric acid to produce a primary amine.

Nucleophilic Substitution of Haloalkanes

Using a large excess of ammonia a haloalkane can be convert to a primary amine by nucleophilic substitution.

Reduction of Amide with NaBH4

Amides can be reduced using sodium borohydride to a primary or secondary amine.

Amines as bases

Amines can accept protons, making them a Bronsted-Lowry base, the aliphatic group(s) attached will affect the strength of the base. We need to be able to compare and give reason for the order of strength of bases of ammonia, primary amines and phenylamine. The strength of the base depends on how available the lone pair is for accepting a proton and primary amines have the most available lone pair, and phenylamine being the least available which gives the following base strength.

The reason for the lone pair being more or less available is related to the positive inductive affect, in methylamine the methyl group pushes electrons towards the nitrogen making the lone pair more available, in the phenyl amine due to overlap of the p orbital in nitrogen and the benezes delocalised ring there is an electron withdrawing affect which makes it a weaker base. Ammonia sits in the middle.

Amines as nucleophiles

A nucleophile is a molecule or ion which can donate a pair of electrons and form bonds between itself and electron deficient parts of molecules.

Reaction with haloalkanes

Amine will react with a haloalkane to initially produce a primary amine the conditions are heated in ethanol.

If a large excess of ammonia is used the major of the product will be the primary alkane, if there is limited amount of ammonia then the reaction will continue to produce a secondary amine.

The reaction can continue to produce a tertiary amine and a quaternary ammonium salt.

If a large excess of the haloalkane is produced the quaternary ammonium salt will be the major product. In this reaction a mixture of products will be made in varying proportions fractional distillation would be used to separate them. Quaternary ammonium salts are often referred to as cationic surfactants, they are used in both fabric and hair conditioner.