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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Amines Know More

  • Libermann's Nitroso Reaction
    Primary, secondary and tertiary amines react differently with nitrous acid.
    Primary amines react with nitrous acid to give an alcohol. Secondary amines react with nitrous acid to produce yellow oily nitrosoamines. The reaction takes place in cold conditions. The yellow solution is then warmed with phenol and sulphuric acid to give a green coloured solution. On adding water, the colour of the solution changes to red. On adding sodium hydroxide the colour changes to greenish blue to violet. This overall reaction is called the Libermann's nitroso reaction. This reaction is only given by secondary amines. Tertiary amines dissolve in nitrous acid to give their nitrite salts.
  • Nomenclature of Amines
    Amines are
    called alkyl amines. They are named by adding the suffix amine to the name of the corresponding alkyl groups. The primary amine is named as the amino derivative and are called aminoalkanes. The prefix amino is added to the name of the parent alkane corresponding to the parent alkane. The carbon atom containing the amino group is given the lowest number. Secondary and tertiary amines are named as N-alkyl aminoalkanes. Depending upon the alkyl groups, they are named as N-alkyl or N,N-dialkyl amino alkanes. If the alkyl groups are different then the largest alkyl group forms the parent alkane and the smaller alkanes are the substituents.
    In the IUPAC system, aliphatic amines are called alkanamines.
  • Basicity of Amines
    Amines have a pyramidal structure like ammonia. The nitrogen atom is sp3 hybridised. The nitrogen atom contains a lone pair which contributes to its basicity. In aliphatic amines, the alkyl group attached is electron releasing which increases the electron density on the nitrogen atom making it more basic. Thus, the alkyl amines are more basic than ammonia. The basicity of alkyl amines is in the order 3 amine > 2 amine > 1 amine. But it is observed that the size of the alkyl group also affects the basicity. More the size of the alkyl group less is the basicity. This effect is called steric hindrance. Thus, the strongest base among the amines is 2 amine.

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