Question

why methane can not be prepared by kolbe's method?

Answer 1

In the Kolbe's reaction an aqueous solution of the sodium or potassium salt of the carboxylic acid is electrolyzed . Alkane is formed at the anode.

CH₃COOK → CH₃COO^- + K⁺

At anode:- CH₃COO^- - e^- → CH₃COO^.

CH₃COO^. → CH₃^. + CO₂

CH₃^. + CH₃^. → C₂H₆

At cathode:-

2 H₂O + 2e^- → 2 OH^- + H₂.

This method is used for the preparation of ethane and the higher alkanes. Methane cannot be prepared by this method because in this reaction two alkyl free radicals combine to form alkane . Thus this reaction require at least two carbon atom ( at least one from each alkyl free radical) . In the methane only single carbon atom is present. Hence it can not be prepared by this reaction.