Phenolphthalein is obtained by heating phthalic anhydride with conc. `H_(2)SO_(4)` and

Options

A. Benzyl alcohol
B. Benzene
C. Phenol
D. Benzoic acid

Answer

To solve the question regarding the synthesis of phenolphthalein, we need to identify the reactants involved in its formation when phthalic anhydride is treated with concentrated sulfuric acid. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Reactants
We know that phenolphthalein is synthesized from phthalic anhydride. The question states that it is heated with concentrated sulfuric acid (H₂SO₄).

**Hint:** Look for the common reactants used in the synthesis of phenolphthalein.

### Step 2: Understand the Reaction
When phthalic anhydride is treated with concentrated sulfuric acid, a dehydration reaction occurs. The concentrated sulfuric acid acts as a dehydrating agent, facilitating the reaction.

**Hint:** Remember that concentrated sulfuric acid can remove water molecules from the reaction mixture.

### Step 3: Analyze the Product Formation
During the reaction, the phthalic anhydride undergoes a transformation where it loses a water molecule. This process leads to the formation of phenolphthalein.

**Hint:** Consider what happens to the structure of phthalic anhydride when it reacts with sulfuric acid.

### Step 4: Identify the Second Reactant
To obtain phenolphthalein, phenol is also required in the reaction. The reaction of phthalic anhydride with phenol in the presence of concentrated sulfuric acid results in the formation of phenolphthalein.

**Hint:** Think about what other organic compounds are commonly used alongside phthalic anhydride in organic synthesis.

### Step 5: Write the Final Reaction
The overall reaction can be summarized as:
\[ \text{Phthalic Anhydride} + \text{Phenol} \xrightarrow{\text{conc. } H_2SO_4} \text{Phenolphthalein} \]

**Hint:** Make sure to visualize the structure of phenolphthalein and how it relates to the reactants.

### Conclusion
Thus, the second product that is used along with phthalic anhydride to obtain phenolphthalein is **phenol**.

**Final Answer:** The answer is **phenol**.