Question

Which of the following represents Etard reaction?

• A. $\text{C}_6\text{H}_5-\text{CH}_3 + \text{CrO}_2\text{Cl}_2 \xrightarrow{\text{(i) } \text{CS}_2, \text{ (ii) } \text{H}_3\text{O}^+} \text{C}_6\text{H}_5\text{CHO}$
• B. $\text{C}_6\text{H}_5-\text{CH}_3 + \text{CrO}_3 + (\text{CH}_3\text{CO})_2\text{O} \xrightarrow{\text{(i) } 273-283\text{ K}, \text{ (ii) } \text{H}_3\text{O}^+, \Delta} \text{C}_6\text{H}_5\text{CHO}$
• C. $\text{C}_6\text{H}_6 + \text{CO} + \text{HCl} \xrightarrow{\text{Anhy. }\text{AlCl}_3} \text{C}_6\text{H}_5\text{CHO}$
• D. $\text{C}_6\text{H}_5\text{COCl} + \text{H}_2 \xrightarrow{\text{Pd-BaSO}_4} \text{C}_6\text{H}_5\text{CHO}$

Hint:

Remember: "Etard reaction uses Chromyl chloride ($\text{CrO}_2\text{Cl}_2$)".
This single reagent association is highly reliable for identifying the reaction in competitive examinations.

Answer 1

The Correct Option is A

Step 1: Rule out the other named reactions first.
Benzene with CO/HCl over anhydrous $\text{AlCl}_3$ is Gattermann-Koch formylation, and acid chloride with $\text{H}_2$ over Pd-BaSO4 is Rosenmund reduction, both genuine routes to benzaldehyde but neither is Etard's reagent.
Step 2: Pin down what actually defines the Etard reaction.
It's specifically chromyl chloride ($\text{CrO}_2\text{Cl}_2$) oxidising a toluene-type methyl group, forming a brown chromium complex in $\text{CS}_2$ solvent.
Step 3: Complete the sequence.
That complex is then hydrolysed with dilute acid to release the aldehyde product.
Step 4: Match this to the options.
Toluene with $\text{CrO}_2\text{Cl}_2$ in $\text{CS}_2$ followed by aqueous workup is exactly the first option.
Final answer: Option 1.