80. Arrange the reactions given below in a proper sequence for the conversion of ethane to methane.

(1) treatment with sodium hydroxide

(2) treatment with aqueous $\mathrm{KOH}$

(3) treatment with $\mathrm{NaOH}+\mathrm{CaO}$

(4) halogenation

(5) reaction with acidified ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$

The correct option is B

4 2 5 1 3

Explanation:

Part (i): Halogenation:

• Ethane $\left({\mathrm{CH}}_3{\mathrm{CH}}_3\right)$ reacts with chlorine $\left({\mathrm{Cl}}_2\right)$ in the presence of light to form Chloroethane $\left({\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}\right)$ and Hydrogen chloride $\left(\mathrm{HCl}\right)$.
• The reaction involved is: ${\mathrm{CH}}_3{\mathrm{CH}}_3+{\mathrm{Cl}}_2\stackrel{\mathrm{light}}{\to }{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}+\mathrm{HCl}$

Part (ii): Treatment with aqueous $\mathrm{KOH}$:

• Chloroethane reacts with aqueous Potassium hydroxide $\mathrm{KOH}$ to form Ethanol $\left({\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\right)$and Potassium chloride $\left(\mathrm{KCl}\right)$
• The reaction involved is: ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Cl}+\mathrm{KOH}\left(\mathrm{aqueous}\right)\to {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}+\mathrm{KCl}$

Part (iii): Reaction with acidified ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$:

• Ethanol is oxidized to Ethanoic acid $\left({\mathrm{CH}}_3\mathrm{COOH}\right)$ in the presence of acidified Potassium dichromate ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$.
• The reaction involved is:${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7}{\to }{\mathrm{CH}}_3\mathrm{COOH}$

Part (iv): Treatment with Sodium hydroxide:

• Ethanoic acid is treated with Sodium hydroxide $\left(\mathrm{NaOH}\right)$ to form Sodium acetate $\left({\mathrm{CH}}_3\mathrm{COONa}\right)$.
• The reaction involved is: ${\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{H}}_2\mathrm{O}$

Part (v): Treatment with $\mathrm{NaOH}+\mathrm{CaO}$:

• Sodium acetate is heated with Soda lime $\mathrm{NaOH}+\mathrm{CaO}$ to form Methane $\left({\mathrm{CH}}_4\right)$ and Sodium carbonate $\left({\mathrm{Na}}_2{\mathrm{CO}}_3\right)$.
• The reaction involved is: ${\mathrm{CH}}_3\mathrm{COONa}+\mathrm{NaOH}\stackrel{\mathrm{CaO},∆}{\to }{\mathrm{CH}}_4+{\mathrm{Na}}_2{\mathrm{CO}}_3$

The correct sequence for the conversion of ethane to methane is 4 2 5 1 3. Hence, option (B) is the correct answer