Question

When chloroform is treated with amine and \[{\rm{KOH}}\], we get:
A. Rose odour smell
B. Sour almond like smell
C. Offensive odour
D. Sour oil of wintergreen like smell

Answer 1

Hint: Alkyl isocyanide is formed when a primary amine is heated with chloroform and potassium hydroxide. This reaction is known as carbylamine reaction.

Complete Step by Step Solution:
Organic compounds containing nitrogen are amines. Also, amines are considered to be derivatives of ammonia in which one or more hydrogen atoms have been replaced by alkyl groups or aryl groups. Primary amines are the compounds in which one hydrogen atom in ammonia is replaced by an alkyl or aryl group. Some examples of primary amines are methylamine, ethylamine, phenyl amine etc.

In carbylamine reaction, primary amine undergoes heating with chloroform and potassium hydroxide to form alkyl isocyanide. Alkyl isocyanide gives a very offensive odour.
The general reaction can be shown as:
\[{\rm{RN}}{{\rm{H}}_{\rm{2}}}\,\,{\rm{ + }}\,\,{\rm{CHC}}{{\rm{l}}_{\rm{3}}}\,\,{\rm{ + }}\,\,{\rm{3KOH}} \to {\rm{RNC}}\,\,{\rm{ + }}\,\,{\rm{3KCl}}\,\,{\rm{ + }}\,{\rm{3}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\]
Here, \[{\rm{RN}}{{\rm{H}}_{\rm{2}}}\]= primary amine
\[{\rm{CHC}}{{\rm{l}}_{\rm{3}}}\]= chloroform
\[{\rm{KOH}}\]= potassium hydroxide
\[{\rm{RNC}}\]= alkyl isocyanide (carbylamine)
\[{\rm{KCl}}\]= potassium chloride
\[{{\rm{H}}_{\rm{2}}}{\rm{O}}\]= water
The above reaction is not shown by secondary and tertiary amine. Hence, this reaction can be used to differentiate primary amines from secondary amines and tertiary amines.

The balanced chemical equation for chloroform reacting with primary amine and potassium hydroxide can be written as shown below:
\[\begin{array}{l}{{\rm{C}}_2}{{\rm{H}}_5}{\rm{N}}{{\rm{H}}_{\rm{2}}}\,\,{\rm{ + }}\,\,{\rm{CHC}}{{\rm{l}}_{\rm{3}}}\,\,{\rm{ + }}\,\,{\rm{3KOH}} \to {{\rm{C}}_2}{{\rm{H}}_5} - {{\rm{N}}^ + } \equiv {{\rm{C}}^ - }\,\,{\rm{ + }}\,\,{\rm{3KCl}}\,\,{\rm{ + }}\,{\rm{3}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\\end{array}\]
Here, \[{{\rm{C}}_2}{{\rm{H}}_5}{\rm{N}}{{\rm{H}}_{\rm{2}}}\]= ethylamine (primary amine)
\[{{\rm{C}}_2}{{\rm{H}}_5} - {{\rm{N}}^ + } \equiv {{\rm{C}}^ - }\]= ethyl isocyanide (carbylamine)

Ethyl isocyanide (carbylamine) is believed to have a very offensive odour.
Therefore, option C is correct.

Note: The mechanism for the reaction is believed to involve the formation of nitrogen ylide by the addition of dichlorocarbene that is formed initially. This is followed by the transfer of proton and further elimination of hydrogen chloride to give the desired product.