Question

Oxidation of toluene to benzaldehyde by the use of chromyl chloride is called

• A. Wurtz reaction
• B. Etard's reaction
• C. Fittig reaction
• D. Rosenmund's reaction

Hint:

The Etard reaction is a selective oxidation method to convert methylbenzenes like toluene into aldehydes using chromyl chloride. It avoids over-oxidation to acids, making it especially valuable in synthetic organic chemistry.

Answer 1

The Correct Option is B

The Etard reaction is a well-established organic process designed to selectively convert methyl groups on aromatic rings into aldehyde groups. The detailed mechanism is as follows:
Step 1: Reactants
The starting material is toluene (\( C_6H_5CH_3 \)).
The key reagent is chromyl chloride (\( CrO_2Cl_2 \)), used in a non-aqueous solvent such as carbon tetrachloride (\( CCl_4 \)).
Step 2: Etard Complex Formation
Chromyl chloride interacts with toluene's methyl group, creating a complex called the "Etard complex." This is a coordination complex, where chromium atoms temporarily bind with the benzylic hydrogen atoms.
Step 3: Complex Hydrolysis
Subsequent hydrolysis with water (typically dilute acid) breaks down the complex, oxidizing the methyl group into a formyl group (\( -CHO \)). \[ C_6H_5CH_3 \xrightarrow{CrO_2Cl_2/CCl_4} \text{Etard Complex} \xrightarrow{H_2O} C_6H_5CHO \]
Step 4: Final Product
The final product of this reaction is benzaldehyde (\( C_6H_5CHO \)).
Summary:
This reaction, named after French chemist Alexandre Etard, is particularly useful for transforming alkylbenzenes into aromatic aldehydes without over-oxidation to acids. This is the rationale for its selection here.