The major product formed when aniline reacts with concentrated H_2SO_4 followed by heating with H_2SO_4 at 453-473k is

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Answer

To solve the question regarding the major product formed when aniline reacts with concentrated H₂SO₄ followed by heating at 453-473 K, we can break down the process into several steps:

### Step 1: Understanding the Reactants
Aniline (C₆H₅NH₂) is an aromatic amine that contains a benzene ring and an amino group (-NH₂). When it reacts with concentrated sulfuric acid (H₂SO₄), we need to consider the nature of the reaction, which is sulfonation.

**Hint:** Identify the structure of aniline and the functional groups present.

### Step 2: Reaction with Concentrated H₂SO₄
When aniline is treated with concentrated H₂SO₄, it forms an intermediate compound known as aniline hydrogen sulfate. This occurs because the amino group (-NH₂) can act as a base and protonate, leading to the formation of the anilinium ion (C₆H₅NH₃⁺) and bisulfate ion (HSO₄⁻).

**Hint:** Consider the protonation of the amino group in the presence of strong acids.

### Step 3: Heating the Intermediate
Upon heating the aniline hydrogen sulfate at temperatures between 453-473 K, the reaction proceeds to form para-amino-benzenesulfonic acid. This is due to the electrophilic substitution reaction where the -SO₃H group from sulfuric acid substitutes at the para position relative to the amino group on the benzene ring.

**Hint:** Recall that electrophilic aromatic substitution reactions often favor substitution at the para position when there is a directing group like -NH₂.

### Step 4: Formation of the Major Product
The major product formed is para-amino-benzenesulfonic acid (C₆H₄(NH₂)(SO₃H)), which has the amino group at the para position to the sulfonic acid group. This compound can also exist in a zwitterionic form, where it has both a positive charge (from the ammonium ion) and a negative charge (from the sulfonate ion).

**Hint:** Visualize the structure of the product to identify the positions of the functional groups.

### Step 5: Conclusion
The major product of the reaction between aniline and concentrated H₂SO₄ followed by heating is para-amino-benzenesulfonic acid, also known as sulfanilic acid.

**Final Answer:** Para-amino-benzenesulfonic acid (sulfanilic acid).