Question

Which of the following reactions do NOT provide an aldehyde as a product?

• A. A
• B. B
• C. C
• D. D

Hint:

Organometallic reagents have varying reactivities:
$\text{R}_2\text{Cd}$ and $\text{R}_2\text{Zn}$ are mild nucleophiles that halt at the ketone stage when reacted with acid chlorides, whereas $\text{RMgX}$ and $\text{RLi}$ are strong nucleophiles that carry the reaction to tertiary alcohols.

Answer 1

The Correct Option is A

Step 1 : Understanding the Question:
The question asks us to identify which of the given organic chemical reactions does not produce an aldehyde as its major product.

Step 2 : Key Formulas and Approach:
The approach involves identifying the name and mechanism of each reaction:

• Reaction (a): Treatment of an acid chloride with a dialkylcadmium reagent.

• Reaction (b): Rosenmund reduction.

• Reaction (c): Stephen reduction.

• Reaction (d): Étard reaction.

Step 3 : Detailed Explanation:
Let us evaluate each reaction individually:

• Reaction (a): Benzoyl chloride is treated with dibenzylcadmium, $(\text{C}_6\text{H}_5\text{CH}_2)_2\text{Cd}$.
Organocadmium reagents are less nucleophilic than Grignard reagents. They react smoothly with acid chlorides to yield ketones, but do not react further to form tertiary alcohols.
The reaction is:
\[ 2\text{C}_6\text{H}_5\text{COCl} + (\text{C}_6\text{H}_5\text{CH}_2)_2\text{Cd} \rightarrow 2\text{C}_6\text{H}_5\text{COCH}_2\text{C}_6\text{H}_5 + \text{CdCl}_2 \]
The product is benzyl phenyl ketone, which is a ketone, not an aldehyde.

• Reaction (b): Benzoyl chloride is reduced with hydrogen gas in the presence of palladium on barium sulfate catalyst ($\text{Pd-BaSO}_4$).
This is the Rosenmund reduction, which selectively reduces acid chlorides to benzaldehyde (an aldehyde).

• Reaction (c): Benzonitrile is reduced using tin(II) chloride ($\text{SnCl}_2$) and $\text{HCl}$, followed by acidic hydrolysis.
This is the Stephen reduction, which converts nitriles to imines, which are then hydrolyzed to benzaldehyde (an aldehyde).

• Reaction (d): Toluene is oxidized using chromyl chloride ($\text{CrO}_2\text{Cl}_2$) in carbon disulfide ($\text{CS}_2$), followed by hydrolysis.
This is the Étard reaction, which selectively oxidizes the methyl group of toluene to form benzaldehyde (an aldehyde).

Step 4 : Final Answer:
Reaction (a) yields a ketone instead of an aldehyde, making it the correct choice.
This corresponds to Option (A).