See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1: Identify the starting material and first reaction. The starting material is acetophenone (Ph-C(=O)-CH3). Treatment with NaNO2/HCl is a nitrosation reaction. The acidic alpha-hydrogen of the methyl group adjacent to the carbonyl is replaced by a nitroso group via reaction with nitrous acid (HNO2, generated in situ from NaNO2 + HCl). This gives Ph-C(=O)-CH=N-OH (the alpha-isonitrosoacetophenone, i.e., the oxime of phenylglyoxal / alpha-oximino acetophenone). So (A) = Ph-C(=O)-CH=N-OH (isonitrosoacetophenone). Step 2: Reaction of (A) with Ac2O/heat. Acetic anhydride with heat converts the oxime (A) into its acetyl derivative and then promotes a Beckmann-type or dehydration rearrangement. More precisely, Ac2O acetylates the oxime OH to give Ph-C(=O)-CH=N-OAc, and upon heating this undergoes rearrangement (analogous to Neber rearrangement or dehydration). Actually, the classical reaction of alpha-oximino ketones with Ac2O/heat produces the isatogen or the nitrile oxide intermediate, but the well-known reaction here is: alpha-oximino acetophenone treated with Ac2O gives the diacetyl derivative which on heating loses acetic acid to give phenylisocyanate or rearranges. The known pathway is that Ac2O converts the oxime to an acetoxy intermediate that dehydrates to give phenacyl nitrile or isonitrile. Actually, the standard result in this reaction sequence is: (A) = Ph-C(=O)-CH=NOH, with Ac2O/heat gives (B) = Ph-C(=O)-CN (benzoyl cyanide / phenacyl isonitrile or phenylglyoxalonitrile). The nitrile group comes from dehydration of the oxime after acetylation. Step 3: Hydrolysis of (B) with H3O+. If (B) = Ph-C(=O)-CN, then acid hydrolysis (H3O+) of the nitrile group converts -CN to -COOH, giving (C) = Ph-C(=O)-COOH (phenylglyoxylic acid / benzoylformic acid). Step 4: Match with options. Ph-C(=O)-CO2H corresponds to option (b). Why other options fail: - (a) Ph-CO2H would require loss of a carbon, not consistent with the reaction. - (c) Ph-C(=O)-CHO is phenylglyoxal; hydrolysis of a nitrile gives acid, not aldehyde. - (d) Ph-C(=O)-CH2OH would require reduction, not acid hydrolysis. Therefore, the correct answer is B.