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 .