On heating with dilute sulphuric acid, naphthalene - 1 sulphonic acid gives predominantly

Options

A. naphthalene
B. naphthalene 2 - sulphonic acid
C. 1 - naphthol
D. 2 - naphthol

Answer

To solve the question, we need to analyze the reaction of naphthalene-1-sulfonic acid when heated with dilute sulfuric acid. Here's a step-by-step solution:

### Step 1: Understand the Structure of Naphthalene-1-Sulfonic Acid
Naphthalene-1-sulfonic acid has a sulfonic acid group (-SO3H) attached to the first carbon of the naphthalene ring. The structure can be visualized as follows:

```
SO3H
|
C1 - C2
/ \
C8 C3
| |
C7 C4
\ /
C6 - C5
```

### Step 2: Heating with Dilute Sulfuric Acid
When naphthalene-1-sulfonic acid is heated with dilute sulfuric acid, the acidic medium facilitates a rearrangement reaction. The hydrogen atom at the second position (C2) of the naphthalene ring can shift to the position of the sulfonic acid group (C1).

### Step 3: Rearrangement Mechanism
This rearrangement is a reversible reaction where the hydrogen atom at C2 moves to C1, and the sulfonic acid group moves to C2. The resulting structure will be:

```
SO3H
|
C1 - C2
/ \
C8 C3
| |
C7 C4
\ /
C6 - C5
```
After the rearrangement, we have naphthalene-2-sulfonic acid.

### Step 4: Naming the Product
The product formed after the rearrangement is naphthalene-2-sulfonic acid. This is because the sulfonic acid group is now located at the second position of the naphthalene ring.

### Step 5: Conclusion
Thus, the predominant product formed when naphthalene-1-sulfonic acid is heated with dilute sulfuric acid is **naphthalene-2-sulfonic acid**.

### Final Answer
The correct answer is **naphthalene-2-sulfonic acid**.

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