Question

A mixture of ethyl iodide and n-propyl iodide is subjected to Wurtz reaction. The hydrocarbon which will not be formed is:
A. butane
B. propane
C. pentane
D. hexane

Answer 1

Hint: Alkanes are generally represented by ${{\text{C}}_{\text{n}}}{{\text{H}}_{2{\text{n}} + 2}}$. Wurtz reaction is one of the oldest organic preparations of alkanes. Alkanes are produced from the Wurtz reaction. This reaction is the treatment of alkyl halides with sodium metal in dry ether. Generally, this reaction produces higher alkanes.

Complete step by step solution:
Wurtz reaction generally produces a dimer which is derived from two alkyl halides. It produces a mixture of products. The two alkyl halides may be the same or different.
General chemical equation of Wurtz reaction is given below:
 ${\text{RX}} + 2{\text{Na}} \to {{\text{R}}^ - }{\text{N}}{{\text{a}}^ + } + {\text{NaX}}$
${{\text{R}}^ - }{\text{N}}{{\text{a}}^ + } + {\text{RX}} \to {\text{R}} - {\text{R}} + {\text{NaX}}$, where ${\text{R}}$ and ${\text{X}}$ are alkanes and halides.
From the question given, we can understand that ethyl iodide and n-propyl iodide are reacted with sodium in the presence of dry ether. The reaction is given below:
${\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{I}} + {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{I}}\xrightarrow[{{\text{ether}}}]{{{\text{Na}}}}{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3} + {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3} + {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3}$
Butane and hexane are self-addition products. While pentane is a cross-addition product. Self-addition products are formed by addition of each reactant with itself, i.e. two equivalents of ethyl iodide produces butane in the presence of sodium metal in dry ether. Also, hexane is produced when two equivalents of n-propyl iodide are reacted with sodium metal in the presence of dry ether. Cross-addition product is formed when both are reacted and undergo Wurtz reaction.
Since the Wurtz reaction produces higher alkanes, propane is not formed.

Hence, the correct option is B.

Note: When ethyl halide and methyl halide is reacted together with sodium metal in the presence of dry ether, propane can be obtained. This also produces other alkanes like butane and ethane. The products are obtained with respect to the reactants.