. Chemical Amine salts on treatment with a base like NaOH, regenerate the parent amine. Amine salts are soluble in water but insoluble in organic solvents like ether. This reaction is the basis for the separation of amines from the non basic organic compounds insoluble in water.
The reaction of amines with mineral acids to form ammonium salts shows that these are basic in nature. Amines have an unshared pair of electrons on nitrogen atom due to which they behave as Lewis base. Basic character of amines can be better understood in terms of their K b and p K b values as explained below: K = R OH R H NH NH or [H O] K = H N H H R R or b K = N H NH H R R p K b = –log K b Larger the value of K b or smaller the value of p K b , stronger is the base. The p K b values of few amines are given in Table .
. p K b value of ammonia is . . Aliphatic amines are stronger bases than ammonia due to +I effect of alkyl groups leading to high electron density on the nitrogen atom.
Their p K b values lie in the range of to . . On the other hand, aromatic amines are weaker bases than ammonia due to the electron withdrawing nature of the aryl group. Name of amine p K b Methanamine .
N -Methylmethanamine . N,N -Dimethylmethanamine . Ethanamine . N -Ethylethanamine .
N,N -Diethylethanamine . Benzenamine . Phenylmethanamine . N -Methylaniline .
N,N -Dimethylaniline . Table . : p K b Values of Amines in Aqueous Phase You may find some discrepancies while trying to interpret the K b values of amines on the basis of +I or –I effect of the substituents present in amines. Besides inductive effect, there are other effects like solvation effect,