Kolbe electrolysis
Electrolysis of an aqueous solution of the sodium or potassium salt of a carboxylic acid gives an alkane at the anode.
Sodium propanoateCH₃CH₂COONaCompound - Step 1
electrolysis of the aqueous solution
ButaneCH₃CH₂CH₂CH₃Alkane
How it works
- At the anode the carboxylate loses an electron and CO₂ to give an alkyl radical.
- Two alkyl radicals combine to form R-R.
- Hydrogen is released at the cathode.
What it makes
Alkanes with 2(n-1) carbons from an acid with n carbons.
Where it fails
Mixed salts give mixtures of alkanes. Methane cannot be made.
Class 11, Chapter 9 Hydrocarbons
Kolbe electrolysis: quick answers
What is formed from sodium ethanoate?
Ethane at the anode (with CO2), and hydrogen at the cathode.
How does Kolbe electrolysis differ from decarboxylation?
Electrolysis joins two alkyl groups; soda lime decarboxylation gives an alkane with one carbon less.
What is formed at the cathode?
Hydrogen gas (and NaOH).