Kolbe's Electrolytic Method

$$2\text{R--COONa} + 2\text{H}_2\text{O} \xrightarrow{\text{Electrolysis}} \text{R--R} + 2\text{CO}_2 + \text{H}_2 + 2\text{NaOH}$$

Concept: Electrolysis of a concentrated aqueous solution of sodium or potassium salt of a carboxylic acid yields a symmetrical alkane containing an even number of carbon atoms at the anode.

Electrode Reactions:

At Anode (Oxidation):

$$2\text{R--COO}^- \xrightarrow{-2e^-} 2\text{R--COO}\cdot \xrightarrow{-2\text{CO}_2} 2\text{R}\cdot \to \text{R--R}$$

At Cathode (Reduction):

$$2\text{H}_2\text{O} + 2e^- \to \text{H}_2\uparrow + 2\text{OH}^-$$

Key Notes:

• As electrolysis proceeds, hydroxide ions ($$\text{OH}^-$$) accumulate near the cathode, causing the pH of the solution to increase (becomes basic).
• Methane ($$\text{CH}_4$$) cannot be prepared by Kolbe's electrolysis.