Question

In the presence of Grignard reagent (RMgX), which of the following is used to prepare a carboxylic acid?

• A. \(NH_{3}\)
• B. \(CO_{2}\) (Dry ice)
• C. \(H_{2}O\)
• D. \(O_{2}\)

Hint:

Important Grignard reactions: \[ \boxed{ \begin{aligned} RMgX+HCHO &\rightarrow 1^\circ \text{ alcohol}\\ RMgX+\text{Aldehyde} &\rightarrow 2^\circ \text{ alcohol}\\ RMgX+\text{Ketone} &\rightarrow 3^\circ \text{ alcohol}\\ RMgX+CO_2 &\rightarrow \text{Carboxylic acid} \end{aligned} } \] Always remember that dry ice (\(CO_2\)) is used to prepare carboxylic acids from Grignard reagents.

Answer 1

The Correct Option is B

A Grignard reagent $RMgX$ reacts with dry carbon dioxide ($CO_2$, i.e., dry ice) via nucleophilic addition to form a magnesium carboxylate salt $RCOOMgX^+$. Subsequent acid hydrolysis liberates the carboxylic acid $RCOOH$, achieving a one-carbon chain extension from the original alkyl halide.