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Chemistry · JEE Advanced only

Aldehydes and Ketones: Preparations from Acid Chlorides, Nitriles, Esters (JEE Advanced)

Not in the JEE Main syllabus, but it is in JEE Advanced. Study time: about 3-4 hours for thorough understanding and practice of all named reactions and their conditions.

Last updated: 26 October 2026

Direct answer

Aldehydes and ketones can be prepared from acid chlorides, nitriles, and esters through controlled reduction or hydrolysis reactions.

Aldehydes and ketones can be prepared from acid chlorides, nitriles, and esters through controlled reduction or hydrolysis reactions. These methods give you precise control over whether you get an aldehyde or ketone as the final product. Understanding the reagents and conditions for each route is essential for JEE Advanced.

Official syllabus

What the JEE Advanced syllabus says

“Preparation of: aldehydes and ketones from acid chlorides and nitriles; aldehydes from esters; benzaldehyde from toluene and benzene”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: Nature of carbonyl group, nucleophilic addition to >C=O group.

JEE Main focuses on the carbonyl group's reactivity and nucleophilic additions, but Advanced expects you to know specific preparation methods from acid derivatives. You need to learn these synthetic routes and the special reagents involved.

Key ideas

What you must understand

  • Acid chlorides undergo partial reduction with Pd-BaSO₄/H₂ (Rosenmund reduction) to give aldehydes; the poisoned catalyst stops reduction at the aldehyde stage
  • Nitriles react with Grignard reagents followed by hydrolysis to give ketones; with SnCl₂/HCl (Stephen reduction), they give aldehydes
  • Esters can be reduced to aldehydes using DIBAL-H (diisobutylaluminium hydride) at low temperature
  • Toluene is oxidized to benzaldehyde using CrO₃ in acetic anhydride (Etard reaction) or by chromyl chloride (CrO₂Cl₂)
  • Benzene can be converted to benzaldehyde via Gattermann-Koch reaction using CO + HCl with AlCl₃/CuCl catalyst
  • The choice of reducing agent determines whether you stop at aldehyde or go all the way to alcohol
Formulas

Formulas and key facts

  • RCOCl + H₂ → RCHO + HCl (Pd-BaSO₄, quinoline, Rosenmund)
  • RCN + SnCl₂ + HCl → RCH=NH·HCl → RCHO (Stephen reduction)
  • RCN + R'MgX → RC(=NMgX)R' → RCOR' (after H₃O⁺)
  • RCOOR' + DIBAL-H → RCHO (at −78°C)
  • C₆H₅CH₃ + CrO₂Cl₂ → C₆H₅CHO (Etard reaction)
  • C₆H₆ + CO + HCl → C₆H₅CHO (Gattermann-Koch, AlCl₃/CuCl)
  • Acid chloride + R₂CuLi → Ketone (Gilman reagent)
Avoid

Common mistakes

  • Confusing Rosenmund reduction (gives aldehyde) with LiAlH₄ reduction of acid chloride (gives alcohol)
  • Forgetting that Stephen reduction works only for aromatic or aliphatic nitriles to give aldehydes, while Grignard on nitriles gives ketones
  • Using DIBAL-H at room temperature instead of low temperature, which leads to over-reduction to alcohol
  • Mixing up Etard reaction (CrO₂Cl₂) with side-chain oxidation using KMnO₄ (which gives carboxylic acid, not aldehyde)
Worked example

A JEE Advanced-level example

Question. An organic compound A (C₇H₅ClO) on treatment with H₂/Pd-BaSO₄ gives compound B (C₇H₆O). Compound B gives positive Tollens test and does not decolorize Baeyer's reagent. Identify A and B, and write the reaction involved.

Show solution
  1. Compound A has molecular formula C₇H₅ClO. The presence of Cl and O suggests an acid chloride. With 7 carbons and a benzene ring pattern, A is likely benzoyl chloride (C₆H₅COCl).
  2. The reaction uses Pd-BaSO₄ with H₂, which is the Rosenmund reduction. This converts acid chlorides to aldehydes.
  3. Compound B (C₇H₆O) gives positive Tollens test, confirming it is an aldehyde. It does not decolorize Baeyer's reagent, meaning no C=C double bond is present.
  4. B must be benzaldehyde (C₆H₅CHO), which fits all observations.
  5. Reaction: C₆H₅COCl + H₂ → C₆H₅CHO + HCl (Pd-BaSO₄, quinoline)

Answer: A is benzoyl chloride (C₆H₅COCl) and B is benzaldehyde (C₆H₅CHO). The reaction is Rosenmund reduction.

Solved twice independently; both solutions agree.

FAQs

Frequently asked questions

Is Aldehydes and Ketones: Preparations from Acid Chlorides, Nitriles, Esters in the JEE Main syllabus?

No. It is in the JEE Advanced 2026 syllabus only. The closest JEE Main topic is Nature of carbonyl group, nucleophilic addition to >C=O group.

How long does Aldehydes and Ketones: Preparations from Acid Chlorides, Nitriles, Esters take to prepare for JEE Advanced?

About 3-4 hours for thorough understanding and practice of all named reactions and their conditions, if you already know the related JEE Main topic.

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