Question

Etard's reaction involves the preparation of Benzaldehyde from:
(A) Toluene
(B) Ethyl benzene
(C) Benzoyl chloride
(D) Sodium benzoate

Answer 1

Hint: Etard’s reaction involves oxidation of a methyl group attached to an aromatic system with Chromyl chloride reagent. This reaction yields corresponding aldehyde as a main product.

Complete step by step answer:
Let’s see the basics about the Etard reaction.
- Etard's reaction is a chemical reaction that involves the direct oxidation of an aromatic methyl group to an aldehyde using chromyl chloride.
- Chromyl chloride is used as an oxidising agent in this reaction. Chromium metal is in +6 oxidation state in Chromyl chloride, so it can oxidise other compounds.
- This reaction is important in synthetic organic chemistry because it oxidises methyl group to –CHO while other oxidising agents directly oxidise it to –COOH group only. Such as $KMn{{O}_{4}},{{K}_{2}}C{{r}_{2}}{{O}_{7}}$ oxidises methyl group directly to the corresponding carboxylic acid.
- The mechanism of this reaction involves a reaction followed by sigmatropic rearrangement.

For example, Toluene can be oxidized to benzaldehyde by Etard reaction.

-Here, we can see that the methyl group of toluene is an aromatic methyl group and so it can be oxidised by Chromyl chloride to corresponding aldehydes. If a methyl group is attached to any aromatic heterocyclic ring, then also this reaction is possible. So, when toluene will react with Chromyl chloride, it will give benzaldehyde as a main product.
So, the correct answer is “Option C”.

Note: Remember that if an ethyl group or any other alkyl chain other than methyl is attached to the aromatic ring, then it cannot give aldehyde as a product. Instead, they will give ketone products with ketone group on the carbon which is directly attached with an aromatic ring.