Which of the following reactants on reaction with conc. NaOH followed by acidification gives the following lactone as the only product?
(A)(see structure)
(B)(see structure)
(C)(see structure)✓ Correct
(D)(see structure)
Answer: (C)
Solution
The product is phthalide, a lactone formed from phthalaldehyde (benzene-1,2-dicarbaldehyde). When phthalaldehyde is treated with concentrated NaOH, it undergoes an intramolecular Cannizzaro reaction. One aldehyde group is oxidized to a carboxylate while the other is reduced to a hydroxymethyl group. Upon acidification, the carboxylic acid and the hydroxymethyl group on adjacent carbons cyclize to form the lactone (phthalide). Option (C) shows phthalaldehyde, which is the correct starting material.
JEE Advanced · 2006 · 09 Apr 2006 · One or more correct options
