Which of the following is most reactive towards sulphonation ?

Options

A. m-Xylene
B. o-Xylene
C. Toluene
D. p-Xylene

Answer

To determine which compound is most reactive towards sulfonation, we need to analyze the electron density in the aromatic rings of the given compounds: Metazoline, Orthoziline, Toluene, and Paraziline. Sulfonation is an electrophilic substitution reaction, where an electrophile (in this case, SO3) attacks the aromatic ring.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Metazoline
- Orthoziline
- Toluene
- Paraziline

2. **Understand Sulfonation**:
- Sulfonation involves the attack of an electrophile (SO3) on the aromatic ring.
- The reactivity of the aromatic compound towards sulfonation depends on the electron density of the ring.

3. **Analyze the Electron Donating Groups**:
- Toluene has a methyl group (–CH3) which is an electron-donating group. It increases the electron density of the ring, making it more reactive towards electrophiles.
- Both ortho and para positions relative to the methyl group will have increased electron density due to the +I (inductive) effect and hyperconjugation.

4. **Analyze Metazoline and Orthoziline**:
- In Metazoline, the methyl group is in the meta position relative to the nitrogen atom. The electron density is increased at the ortho and para positions but less effectively at the meta position.
- In Orthoziline, the methyl groups are at the ortho positions, which increases electron density at the ortho and para positions.

5. **Analyze Paraziline**:
- Paraziline has methyl groups at the para positions. This also increases electron density at the ortho and para positions.

6. **Comparison of Reactivity**:
- Toluene has the highest electron density due to the methyl group.
- Metazoline has a lower electron density compared to Toluene but higher than Orthoziline and Paraziline due to the arrangement of substituents.
- Orthoziline and Paraziline have lower reactivity due to the positioning of the electron-donating groups which do not effectively increase electron density at the site of electrophilic attack.

7. **Conclusion**:
- Among the given options, Toluene is the most reactive towards sulfonation because it has the highest electron density on the aromatic ring due to the presence of the methyl group.

### Final Answer:
**Toluene is the most reactive towards sulfonation.**