The major product obtained on interaction of phenol with sodium hydroxide and carbon dioxide is
(a)

Q: Why does $CO_2$ act as an electrophile?

Carbon dioxide has a central carbon atom double-bonded to two highly electronegative oxygen atoms. This pulls electron density away from the carbon, making it electron-deficient and susceptible to nucleophilic attack.

Q: Why is the ortho product major and not para?

The sodium ion ($Na^+$) coordinates with both the phenoxide oxygen and the incoming $CO_2$ oxygen, stabilizing the transition state specifically at the ortho position. This chelation effect makes the ortho product dominant.

Q: What happens if we use $KOH$ instead of $NaOH$?

Interestingly, if you use potassium hydroxide ($KOH$), the para product becomes the major product! The potassium ion is larger and cannot effectively chelate the two oxygen atoms, so steric hindrance pushes the substitution to the para position.

Q: Can phenol react with $CO_2$ without $NaOH$?

No, phenol is not nucleophilic enough to attack a weak electrophile like $CO_2$. Converting it to the phenoxide ion using $NaOH$ drastically increases the electron density in the ring, enabling the reaction.

Q: What is the difference between Kolbe's and Reimer-Tiemann reaction?

Both are electrophilic aromatic substitutions on phenol. Kolbe's reaction uses $CO_2$ to add a carboxylic acid group ($-COOH$), yielding salicylic acid. Reimer-Tiemann uses chloroform ($CHCl_3$) to add an aldehyde group ($-CHO$), yielding salicylaldehyde.

Question

The major product obtained on interaction of phenol with sodium hydroxide and carbon dioxide is

Options:

(A) benzoic acid

(B) salicylaldehyde

(C) salicylic acid

(D) phthalic acid

Sigma Percentile · Accepted Answer

### The Magic of Kolbe's Reaction

Welcome to one of the most elegant and historically significant reactions in organic chemistry! When we mix phenol with sodium hydroxide and carbon dioxide, we aren't just performing a random chemical combination; we are executing the famous **Kolbe's reaction** (also known as the Kolbe-Schmitt reaction).

This reaction is the gateway to synthesizing a compound that has cured billions of headaches worldwide. Let's break down the chemistry step by step.

### Activating the Phenol Ring

Phenol itself is a decent nucleophile, but carbon dioxide ($CO_2$) is a very weak electrophile. If we just bubble $CO_2$ through phenol, nothing much happens. We need to supercharge our phenol!

This is where sodium hydroxide ($NaOH$) comes into play. The base abstracts the acidic proton from phenol, converting it into the **phenoxide ion**.

$$C_6H_5OH + NaOH \rightarrow C_6H_5O^-Na^+ + H_2O$$

The phenoxide ion is significantly more reactive towards electrophilic aromatic substitution than phenol. The negative charge on the oxygen atom delocalizes into the benzene ring, making the ortho and para positions highly electron-rich.

### The Electrophilic Attack

Now that our ring is activated, we introduce carbon dioxide. Even though $CO_2$ is a weak electrophile, the highly reactive phenoxide ion attacks the electron-deficient carbon atom of $CO_2$.

Interestingly, this attack happens predominantly at the **ortho position**. Why? Because the sodium ion ($Na^+$) acts as a chelating agent, coordinating with both the phenoxide oxygen and the oxygen of the incoming $CO_2$ molecule. This stabilizes the transition state at the ortho position, leading to the formation of **sodium salicylate** as the major intermediate.

### The Final Acidification

We are almost there! We have sodium salicylate, but we want the free acid. To achieve this, we perform a simple acidification step by adding a dilute acid (providing $H^+$ ions).

The acid protonates the carboxylate group, replacing the sodium ion and yielding our final, glorious product: **salicylic acid** (also known as $o$-hydroxybenzoic acid).

### The Way Forward: From Salicylic Acid to Aspirin

Salicylic acid is incredibly stable due to **intramolecular hydrogen bonding** between the $-OH$ and $-COOH$ groups. But its story doesn't end here.

If you take salicylic acid and react it with acetic anhydride, you perform an acetylation reaction on the hydroxyl group. The product of this reaction is acetylsalicylic acid, universally known as **Aspirin**! Understanding Kolbe's reaction is literally understanding the foundation of modern pharmaceuticals.

Animated Solution for Chemistry - Organic Chemistry: The major product obtained on interaction of phenol with sodium hydroxide and carbon dioxide is

Select Answer:

Visualized Solution

$Reactants$

$Reagents$

$Intermediate Formation$

$Acidification$

$Final Product$

$Significance$

The Sigma Insight: Alcohols, Phenols, Ethers

The Magic of Kolbe's Reaction

Activating the Phenol Ring

The Electrophilic Attack

The Final Acidification

The Way Forward

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