Phenolphthalein can be prepared by reaction of phenol and

Options

A. phthalic anhydride
B. phathalic acid
C. terephthalic acid
D. all of these

Answer

To prepare phenolphthalein, we need to react phenol with phthalic anhydride in the presence of an acid catalyst. Here’s a step-by-step breakdown of the reaction:

### Step 1: Identify the Reactants
- **Reactants**: Phenol (C6H5OH) and Phthalic Anhydride (C8H4O3).
- **Catalyst**: Concentrated sulfuric acid (H2SO4) is used to facilitate the reaction.

### Step 2: Understand the Structure of Phthalic Anhydride
- Phthalic anhydride can be derived from phthalic acid by removing a water molecule (dehydration).
- The structure of phthalic anhydride consists of two carbonyl groups (C=O) connected by an oxygen atom.

### Step 3: Reaction Mechanism
1. **Formation of Phenolate Ion**:
- In the presence of sulfuric acid, phenol can lose a proton (H+) to form a phenolate ion (C6H5O^-).

2. **Nucleophilic Attack**:
- The phenolate ion acts as a nucleophile and attacks the electrophilic carbon of the phthalic anhydride, leading to the formation of a tetrahedral intermediate.

3. **Formation of Phenolphthalein**:
- The tetrahedral intermediate collapses, resulting in the elimination of a water molecule and the formation of phenolphthalein (C20H14O4).
- The final structure of phenolphthalein includes two phenolic groups linked by a phthalate moiety.

### Step 4: Final Product
- The final product, phenolphthalein, is an organic compound that serves as a pH indicator, turning pink in alkaline solutions and remaining colorless in acidic solutions.

### Summary of Reaction:
- **Overall Reaction**:
\[ 2 \text{C}_6\text{H}_5\text{OH} + \text{C}_8\text{H}_4\text{O}_3 \xrightarrow{\text{H}_2\text{SO}_4} \text{C}_{20}\text{H}_{14}\text{O}_4 + \text{H}_2\text{O} \]

### Conclusion:
- Phenolphthalein can be prepared by the reaction of phenol with phthalic anhydride in the presence of concentrated sulfuric acid.

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