See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The Cannizzaro reaction occurs between two aldehydes that have no alpha-hydrogen atoms under concentrated base conditions. When two different aldehydes are used, a crossed Cannizzaro reaction takes place. Step 1 – Identify the reaction type: 3,4-dimethoxybenzaldehyde (an aromatic aldehyde with no alpha-H) reacts with formaldehyde (HCHO, also no alpha-H) in the presence of concentrated NaOH. This is a crossed Cannizzaro reaction. Step 2 – Determine the relative reactivity: In a crossed Cannizzaro reaction, formaldehyde is preferentially oxidized (it is the better hydride donor due to its small size and high electrophilicity toward nucleophilic addition, and it is more readily oxidized). Formaldehyde acts as the reducing agent (hydride donor) and is itself oxidized to formate (HCO2(-)). Step 3 – Determine the products: The hydride from formaldehyde is transferred to the carbonyl carbon of 3,4-dimethoxybenzaldehyde, reducing it to the corresponding benzyl alcohol: 3,4-dimethoxybenzyl alcohol (CH2OH on the ring). Formaldehyde is simultaneously oxidized to formate ion (HCO2(-)). Step 4 – Confirm the products: Product 1 = 3,4-dimethoxybenzyl alcohol (the aromatic aldehyde is reduced to alcohol). Product 2 = HCO2(-) (formate ion, the oxidation product of formaldehyde). Step 5 – Eliminate other options: - Option (a): Shows CH3OH as the byproduct, which would require formaldehyde to be reduced to methanol, meaning the aromatic aldehyde is oxidized. This does not occur preferentially because HCHO is more easily oxidized. - Options (c) and (d): Show a carboxylic acid (COOH) as the product from the aromatic aldehyde, implying oxidation of the aryl aldehyde, which does not occur in Cannizzaro; Cannizzaro involves disproportionation (one oxidized, one reduced) not further oxidation to acid. - Option (b) correctly shows 3,4-dimethoxybenzyl alcohol + HCO2(-), consistent with the crossed Cannizzaro mechanism where HCHO is oxidized to formate and the aryl aldehyde is reduced to the benzyl alcohol. Therefore, the correct answer is B.