See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The starting material is 2-phenyl-1,3-dioxolane, which is a cyclic acetal formed from benzaldehyde (PhCHO) and ethylene glycol (HOCH2CH2OH). The reaction shown is the hydrolysis (deprotection) of this acetal back to the parent aldehyde and diol. Step 1 - Identify the functional group: The starting material is a cyclic acetal. Acetals are stable under basic and neutral conditions but are readily hydrolyzed under acidic aqueous conditions. Step 2 - Mechanism of acetal hydrolysis: Under acidic conditions (H2SO4 catalyst) with water and heat, the acetal undergoes acid-catalyzed hydrolysis. A lone pair on one of the ring oxygens is protonated, facilitating C-O bond cleavage to form an oxocarbenium ion intermediate. Water then attacks this intermediate, and after proton transfers, the acetal is converted back to the aldehyde (benzaldehyde) and the diol (ethylene glycol). Step 3 - Why option (b) is correct: H2O, H2SO4 (acid catalyst), and heat provide the acidic aqueous conditions necessary for acetal hydrolysis. This is the standard method for deprotecting an acetal to regenerate the carbonyl compound. Step 4 - Why other options fail: - (a) LiAlH4 followed by H2O: LiAlH4 is a strong reducing agent. It would reduce the acetal but does not hydrolyze it back to the aldehyde; it would give an alcohol product instead. - (c) H2O, NaOH, heat: Acetals are stable under basic conditions. Base-catalyzed hydrolysis of acetals does not occur readily because there is no mechanism to protonate and activate the C-O bond under basic conditions. - (d) PCC, CH2Cl2: PCC is an oxidizing agent used to oxidize primary alcohols to aldehydes or secondary alcohols to ketones. It does not hydrolyze acetals. Therefore, the correct answer is B.