JEE Main · 2022 · 26 Jun 2022 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Oxidation of toluene to Benzaldehyde can be easily carried out with which of the following reagents?

(A) $CrO X_{3}$ /acetic acid, $H X_{3} O X^{+}$
(B) $CrO X_{3}$ /acetic anhydride, $H X_{3} O X^{+}$ ✓ Correct
(C) $KMnO X_{4} / HCl$ , $H X_{3} O X^{+}$
(D) $CO / HCl$ , anhydrous $AlCl X_{3}$

Answer: (B)

Solution

The oxidation of toluene to benzaldehyde requires a controlled oxidation that stops at the aldehyde stage without further oxidation to benzoic acid.

Etard reaction: Toluene is oxidized with chromyl chloride (

CrO X_{2} Cl X_{2}

) or

CrO X_{3}

in acetic anhydride (Ac₂O) to give benzaldehyde. The acetic anhydride prevents over-oxidation.

Other reagents:

$CrO X_{3}$ /acetic acid or $KMnO X_{4}$ would oxidize toluene all the way to benzoic acid
$CO / HCl$ with $AlCl X_{3}$ is the Gattermann-Koch reaction for formylation, not oxidation of a methyl group

Therefore,

CrO X_{3}

/acetic anhydride,

H X_{3} O X^{+}

is the correct reagent.

JEE Main · 2022 · 26 Jun 2022 · Shift 2 · Single correct option

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JEE Main · 2022 · 26 Jun 2022 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Solution

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