Question

The correct rank order of orientation of sulfonation in toluene is:

• A. 2-methylbenzenesulfonic Acid > 3-methylbenzenesul-fonic acid > 4-methylbenzenesulfonic acid
• B. 3-methylbenzenesulfonic acid > 2-methylbenzenesul- fonic acid > 4-methylbenzenesulfonic acid
• C. 3-methylbenzenesulfonic acid > 2-methylbenzenesul-fonic acid > 4-methylbenzenesulfonic acid
• D. 4-methylbenzenesulfonic acid > 2-methylbenzenesulfonicacid > 3-methylbenzenesulfonic acid

Answer 1

The Correct Option is D

The question asks for the rank order of orientation of sulfonation in toluene, focusing on the regioselectivity of the electrophilic aromatic substitution reaction, which is crucial in organic chemistry.

Background: Sulfonation of toluene is an example of electrophilic aromatic substitution where a sulfonic acid group (-\text{SO}_3\text{H}) is introduced onto the benzene ring. Toluene is methylbenzene, and the methyl group is an ortho/para-directing group due to the electron-donating nature of the methyl group. This results in a higher electron density at the ortho and para positions.

Step-by-step reasoning:

1. Ortho and Para Positions: In toluene, the methyl group increases electron density at the ortho (2, 6) and para (4) positions. This makes these positions more reactive towards electrophilic substitution compared to the meta position (3, 5).
2. Preference Order: Typically, sulfonation favors the para position over the ortho position due to less steric hindrance. Therefore, the para sulfonic acid derivative (4-methylbenzenesulfonic acid) is generally preferred over ortho (2-methylbenzenesulfonic acid).
3. Meta Position: The meta position is the least favored by an ortho/para directing group like the methyl group, making 3-methylbenzenesulfonic acid the least likely product.

Conclusion: The correct rank order for the sulfonation of toluene is 4-methylbenzenesulfonic acid > 2-methylbenzenesulfonic acid > 3-methylbenzenesulfonic acid. This matches the provided correct answer of 4-methylbenzenesulfonic acid > 2-methylbenzenesulfonicacid > 3-methylbenzenesulfonic acid.

The presence of the electron-donating methyl group favors the para position, followed by the ortho, confirming the observed order.