Question

How to convert $C{H_3}C{H_2}CN$ to $C{H_3}C{H_2}C{H_3}$?

Answer 1

Hint: In organic chemistry, the reactions in which there is a gain in the electronegative element or loss in the electropositive element is known as oxidation reaction whereas the reaction in which there is a gain in electropositive element or a loss in electronegative element is termed as reduction reaction. For the given conversion, as the nitrogen atom which is electronegative is removed from the compound, so we can say that $C{H_3}C{H_2}CN$ is reduced to $C{H_3}C{H_2}C{H_3}$.

Complete answer:
The given conversion can be done by the following reaction mechanism:
Step-1: Reduction of propionitrile in the presence of lithium aluminium hydride:
When $C{H_3}C{H_2}CN$ reacts with $LiAl{H_4}$, then the $CN$ bond in the compound is reduced to $C{H_2} - N{H_2}$. The reaction takes place as follows:
$C{H_3}C{H_2}CN\xrightarrow{{LiAl{H_4}}}C{H_3}C{H_2}C{H_2}N{H_2}$
Step-2: Reaction of primary amine formed, with sodium nitrate in the presence of hydrochloric acid.
When the primary amine reacts with $NaN{O_2}$ in the presence of $HCl$, then the formation of respective alcohol takes place. The reaction proceeds as follows:
$C{H_3}C{H_2}C{H_2}N{H_2} + NaN{O_2}\xrightarrow{{HCl}}C{H_3}C{H_2}(OH)C{H_3}$
Step-3: Reaction with concentrated sulphuric acid.
The alcohol formed, when heated in the presence of concentrated ${H_2}S{O_4}$ which is a dehydrating agent. The formation of respective alkene takes place along with the removal of water molecules. The reaction proceeds as follows:
\[C{H_3}C{H_2}(OH)C{H_3}\xrightarrow{{{H_2}S{O_4}}}C{H_3}C{H_2} = C{H_2}\]
Step-4: Reduction of alkene takes place.
When the hydrogen molecule reacts with the alkene formed in the presence of nickel metal, then propane is formed as the product. The reaction takes place as follows:
\[C{H_3}C{H_2} = C{H_2}\xrightarrow[{Ni}]{{{H_2}}}C{H_3}C{H_2}C{H_3}\]
Hence by following the given reaction sequence, $C{H_3}C{H_2}CN$ is converted to $C{H_3}C{H_2}C{H_3}$.

Note:
It is important to note that the given compound propionitrile i.e., $C{H_3}C{H_2}CN$ can directly be converted into propane i.e., $C{H_3}C{H_2}C{H_3}$ by the reaction with red phosphorus in the presence of hydrogen iodide. The reaction proceeds as follows:
$C{H_3}C{H_2}CN\xrightarrow[{HI}]{{{\text{Red P}}}}C{H_3}C{H_2}C{H_3}$