Question

Aqueous solution of the following compound on electrolysis gives ethane

• A. Acetic acid
• B. Acetamide
• C. Potassium acetate
• D. Ethyl acetate

Answer 1

The correct option is C

Potassium acetate

Let's recall Kolbe's electrolysis

The electrolysis of an aqueous solution of sodium/potassium salt of a fatty acid gives higher alkane. Do note that the electrolysis of an aqueous solution of sodium/potassium salt of a dibasic acid gives alkene, whereas the electrolysis of aqueous solution of sodium/potassium salt of dibasic unsaturated fatty acid gives alkyne.

$2RCOONa\stackrel{Electrolysis}{\to }R-R+2C{O}_2+2\stackrel{-}{O}H+H_2$

Therefore,

Mechanism (free radical)

$2RCOONa$ $\to$ $2RCO{O}^{-}$ + $2N{a}^{+}$

At anode (oxidation)

$2RCO{O}^{-}\to 2\stackrel{-}{e}+2RCO\stackrel{\cdot }{O}$
$2\stackrel{-}{e}+2RCO\stackrel{\cdot }{O}\to 2\stackrel{\cdot }{R}+2C{O}_2\uparrow$
$2\stackrel{\cdot }{R}\to R-R$

At cathode (reduction): reduction of $H_{2}O$ takes place since reduction potential of is greater than $N{a}^{⨁}$

$2H_{2}O+2e^{-}\to 2OH+H_2$

Methane cannot be prepared by this method

$2C{H}_{3}COOK+2H_{2}O\stackrel{Electrolysis}{\to }C{H}_3-C{H}_3+2C{O}_2+2KOH+H_2$