Case: Read the passage and answer the following questions

Aldehydes and ketones are generally prepared by oxidation of primary and secondary alcohols. Dehydrogenation of alcohols gives aldehydes and ketones. Ozonolysis alkenes give aldehydes ketones or a mixture of both depending on the substitution pattern of the alkene. Aldehydes are prepared from acyl chloride, nitrile, esters and even from hydrocarbons by different kinds of oxidation. Ketones are prepared from benzene or its derivatives through Friedel-Crafts acylation reaction. Carboxylic acids are prepared from aldehydes and ketones on oxidation. Nitriles are hydrolysed to amides and then to carboxylic acids. It is even prepared using Grignard’s reagent.

What is the name of the reaction in which toluene is oxidized to benzaldehyde by chromyl chloride?

Etard reaction

The correct answer is option 4. Etard reaction.

The name of the reaction in which toluene is oxidized to benzaldehyde by chromyl chloride is the Etard reaction.

This reaction is a specialized method for the partial oxidation of an aromatic methyl group to an aldehyde group.

Understanding the Etard Reaction

• Reagent: Chromyl chloride ($CrO_{2}Cl_{2}$) in a solvent like carbon tetrachloride ($CCl_{4}$) or carbon disulfide ($CS_{2}$).
• The Intermediate: The chromyl chloride oxidizes the methyl group to form a brown-colored chromium complex.
• Hydrolysis: Subsequent hydrolysis of this chromium complex with water yields the final product, Benzaldehyde.

Why the other options are incorrect:

• Fittig reaction: Used for the coupling of two aryl halides to form a diaryl compound using metallic sodium.
• Rosenmund reaction: The reduction of an acyl chloride to an aldehyde using $H_{2}/Pd/BaSO_{4}$.
• Stephen reaction: The reduction of a nitrile to an aldehyde using $SnCl_{2}/HCl$.

Summary of Oxidizing Toluene

While many strong oxidizing agents (like acidified $KMnO_{4}$) would oxidize toluene all the way to benzoic acid, the Etard reaction is prized because it stops specifically at the aldehyde stage.