Question

Identify the reactant, reagent and condition of Kolbe's reaction from following.

• A. $\text{C}_6\text{H}_5\text{ONa}$, $\text{CO}_2$ and $398\text{ K}$, $6\text{ atm}$
• B. $\text{C}_6\text{H}_5\text{ONa}$, $\text{Na}_2\text{CO}_3$ and $398\text{ K}$
• C. $\text{C}_6\text{H}_5\text{OH}$, $\text{CHCl}_3$ and aq. NaOH
• D. $\text{C}_6\text{H}_5\text{OH}$, dil. $\text{HNO}_3$ and $413\text{ K}$

Hint:

To remember Kolbe's vs Reimer-Tiemann:
Kolbe uses Carbon dioxide ($\text{CO}_2$) to make an Acid (Salicylic acid).
Reimer-Tiemann uses chloRoform ($\text{CHCl}_3$) to make an Aldehyde (Salicylaldehyde).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the correct starting material (reactant), the chemical reagent, and the specific temperature/pressure conditions required for Kolbe's reaction (also known as the Kolbe-Schmitt reaction).

Step 2: Key Formula or Approach:
Kolbe's reaction is a carboxylation reaction used to convert phenol into salicylic acid (2-hydroxybenzoic acid).
The active reactant is not phenol itself, but rather its sodium salt, sodium phenoxide.
The electrophile in this reaction is carbon dioxide ($\text{CO}_2$).

Step 3: Detailed Explanation:
Let's analyze the options:
(C) represents the Reimer-Tiemann reaction, which uses phenol, chloroform, and a base to produce salicylaldehyde.
(D) represents the nitration of phenol.
(A) correctly lists sodium phenoxide ($\text{C}_6\text{H}_5\text{ONa}$) as the reactant and $\text{CO}_2$ as the reagent. The standard conditions for this electrophilic aromatic substitution are a temperature of roughly $398 - 400\text{ K}$ and an elevated pressure of $4 - 7\text{ atm}$. Under these conditions, sodium salicylate is formed, which upon subsequent acidification yields salicylic acid.

Step 4: Final Answer:
The correct combination is $\text{C}_6\text{H}_5\text{ONa}$, $\text{CO}_2$ and $398\text{ K}$, $6\text{ atm}$, matching option (A).