JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Which one of the following reactions will not form acetaldehyde?

(A) $CH_{2} = CH_{2} + O_{2} Pd (II) / Cu (II) H_{2} O$
(B) $CH_{3} CH_{2} OH Cu 573 K$
(C) $CH_{3} CH_{2} OH CrO_{3} - H_{2} SO_{4}$ ✓ Correct
(D) $CH_{3} CN i) DIBAL-H ii) H_{2} O$

Answer: (C)

Solution

Ethene with oxygen over

Pd (II) / Cu (II)

in water is the Wacker oxidation, which stops cleanly at acetaldehyde. Ethanol passed over copper at 573 K is dehydrogenated, and a primary alcohol dehydrogenated this way gives the aldehyde. Acetonitrile with DIBAL-H is reduced only as far as the imine salt, and hydrolysis of that salt gives acetaldehyde. Chromium trioxide in sulfuric acid, however, is a strong oxidant in aqueous acid: the aldehyde it first forms is hydrated and oxidised further, so ethanol under these conditions gives acetic acid rather than acetaldehyde.

JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

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