Which of the following intermediates are involved in the acid catalyzed esterification of carboxylic acid?

Options

A.
B.
C.
D.

Answer

To solve the question regarding the intermediates involved in the acid-catalyzed esterification of carboxylic acids, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The acid-catalyzed esterification involves a carboxylic acid reacting with an alcohol in the presence of an acid catalyst (usually sulfuric acid). This reaction forms an ester and water.

2. **Formation of the Protonated Carboxylic Acid**:
The first step is the protonation of the carboxylic acid. The lone pair of electrons on the oxygen of the carbonyl group (C=O) attacks a proton (H⁺) from the acid catalyst, resulting in a protonated carboxylic acid (R-C(OH)₂⁺).

3. **Nucleophilic Attack by Alcohol**:
The alcohol (ROH) acts as a nucleophile and attacks the electrophilic carbon of the protonated carboxylic acid. This forms a tetrahedral intermediate (R-C(OH)(OR)⁺).

4. **Proton Transfer**:
A proton transfer occurs within the tetrahedral intermediate. The hydroxyl group (OH) that is now positively charged can lose a proton, leading to the formation of a new intermediate (R-C(OH)(OR)₂).

5. **Formation of the Ester**:
The tetrahedral intermediate collapses, leading to the elimination of water (H₂O) and forming the ester (R-C(=O)(OR) + H⁺).

6. **Identifying Intermediates**:
The intermediates formed during these steps include:
- Protonated carboxylic acid (R-C(OH)₂⁺)
- Tetrahedral intermediate (R-C(OH)(OR)⁺)
- Another tetrahedral intermediate before the final collapse (R-C(OH)(OR)₂)

### Conclusion:
Based on the above steps, the intermediates involved in the acid-catalyzed esterification of carboxylic acids include the protonated carboxylic acid and the tetrahedral intermediates. Therefore, the correct options among the given choices would be those that match these intermediates.