In Hofmann degradation reaction, the amine formed has one carbon less than the parent amide. To obtain primary amine with same number of carbon atoms from primary amide, reduction is done with LiAlH4 / ether.
Physical Properties of Amines
1. The lower aliphatic amines are gases with fishy smell.
2. Primary amines witb three or more carbon atoms are liquid and higher members are all solids.
3. Lower aliphatic amines are water suluble because they can form hydrogen bonds with water molecules, however the solubility decreases with increase in hydrophobic alkyl group.
4. Boiling points order primary > secondary > tertiary
5. Tertiary amines does not have intermolecular association due to the absence of hydrogen atom available for hydrogen bond formation.
Basic Strength of Amines
Amines act as Lewis bases due to the presence of lone pair of electrons on the nitrogen atom.
More the Kb( dissociation constant of base), higher is the basicity of amines.
Lesser the pKb‘ higher is the basicity of amines.
Aliphatic amines( CH3NH2) are stronger bases than NH3 due to the electron releasing +/ effect of the alkyl group.
Among aliphatic methyl amines, the order of basic strength in aqueous solution is as follows
( C2H5NH >( C2H5) 3N > C2H5NH2 > NH3
( CH3) 2NH > CH3NH2 >( CH3) 3N > NH3
Aromatic amines are weaker basesthan aliphatic amlnes and NH3, due to the fact that the electron pair on the nitrogen atom is involved in resonance with the π-electron pairs of the ring.