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Butanoic acid (CH3CH2CH2COOH) is subjected to the following two-step reaction sequence: (i) NaOH followed by electrolysis (Kolbe electrolysis); (ii) Cr2O3 catalyst at 780 K and 20 atm pressure. How many sp² carbon atoms are present in the final product P?

1. 6
2. 4
3. 3
4. 2

Correct answer: 6

Solution

Kolbe electrolysis of CH3CH2CH2COO⁻ decarboxylates and couples two propyl radicals to give n-hexane (C6H14). Cr2O3 at 780 K / 20 atm then causes catalytic dehydrogenation and cyclisation (aromatisation) to give benzene (C6H6), which has 6 sp² carbon atoms.

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