Physical properties of aromatic amines

Hydrogen bonding significantly influences the properties of primary and secondary amines. Thus the boiling point of amines is higher than those of the corresponding phosphines, but generally lower than those of the corresponding alcohols. For example, methylamine and ethylamine are gases under standard conditions, whereas the corresponding methyl alcohol and ethyl alcohols are liquids. Gaseous amines possess a characteristic ammonia smell, liquid amines have a distinctive "fishy" smell.

Also reflecting their ability to form hydrogen bonds, most aliphatic amines display some solubility in water. Solubility decreases with the increase in the number of carbon atoms. Aliphatic amines display significant solubility in organic solvents, especially polar organic solvents. Primary amines react with ketones such as acetone, and most amines are incompatible with chloroform and carbon tetrachloride.

The aromatic amines, such as aniline, have their lone pair electrons conjugated into the benzene ring, thus their tendency to engage in hydrogen bonding is diminished. Their boiling points are high and their solubility in water low

Chemical properties of aromatic amines

The reactions of amines are mainly due to participation of unshared pair of electrons of nitrogen which makes them react as a nucleophile or a base (A nucleophile is a species that attacks an electron - deficient carbon and a base is a species that attacks an electron deficient hydrogen i.e., proton)

In aromatic amines, the unshared pair of electrons on the N atom facilitates electrophilic substitution in the phenyl ring. The number of hydrogen atoms on the amine ring also effect the reactions.

Salt formation

Amines being basic react with acids to form salts.

Salts of amines are typical ionic solids. Amine salts are soluble in water but insoluble in non-polar solvents. The aqueous solutions of these amines on treatment with aqueous hydroxide regenerate the amines.