Chapter 16.SE, Problem 51AP

Interpretation Introduction

a)

Interpretation:

The major product(s) obtainable from sulfonation of fluorobenzene is/are to be predicted.

Concept introduction:

Aromatic rings can be sulfonated by using fuming sulfuric acid, a mixture of H₂SO₄ and SO₃. The electrophile is either SO₃H⁺ or SO₃ depending on the reaction conditions. Sulfonation is a reversible process. Sulfonation is favored in strong acid, but desulfonation is favored in hot, dilute aqueous acid.

The substituents attached to the ring have a strong influence on the incoming electrophile. Electron releasing substituent groups, except halogens, activate the ring and direct the incoming electrophile to the o- and p- positions. Halogens are o- and p- directors but they deactivate the ring. Electron withdrawing substituent groups deactivate the ring and direct the incoming electrophile to the m- position.

To predict:

The major products obtainable from sulfonation of fluorobenzene.

Answer to Problem 51AP

The major products obtainable from sulfonation of fluorobenzene are o-flurobenzenesulfonic acid and p- flurobenzenesulfonic acid.

Explanation of Solution

Fluorine attached to an aromatic ring is an o- and p- directing deactivating group. Hence it directs the electrophile, SO₃H⁺ to these positions.

Conclusion

The major products obtainable from sulfonation of fluorobenzene are o-flurobenzenesulfonic acid and p- flurobenzenesulfonic acid.

Interpretation Introduction

b)

Interpretation:

The major product(s) obtainable from sulfonation of m-bromophenol is/are to be predicted.

Concept introduction:

Electrophilic substitution of disubstituted benzenes follows three simple rules. (i) If the directing influence of both the substituents reinforce each other, a single product results. (ii) If the directing influences of both the substituent groups oppose each other, the most powerful activating group among them has the dominant influence but usually a mixture of products results. (iii) In meta disubstituted compounds, further substitution in between the groups occurs only rarely, due to steric reasons.

To predict:

The major product(s) obtainable from sulfonation of m-bromophenol.

Answer to Problem 51AP

The major products produced during the sulfonation of m-bromophenol are 2-bromo-4-hydroxybenzenesulfonicacid (I) and 4-bromo-2-hydroxybenzenesulfonicacid (II).

Explanation of Solution

The Br is an ortho and para directing and deactivating group while -OH group is also an ortho and para directing and highly activating group. Hence the -OH group decides the position at which the electrophilic substitution reaction will occur. The electrophile, SO₃H⁺, enters into the ortho and para positions with respect to -OH group to produce 2-bromo-4-hydroxybenzenesulfonicacid (I) and 4-bromo-2-hydroxybenzenesulfonicacid (II).

Conclusion

The major products produced during the sulfonation of m-bromophenol are 2-bromo-4-hydroxybenzenesulfonicacid (I) and 4-bromo-2-hydroxybenzenesulfonicacid (II).

Interpretation Introduction

c)

Interpretation:

The major product(s) obtainable from sulfonation of m-dichlorobenzene is/are to be predicted.

Concept introduction:

Electrophilic substitution of disubstituted benzenes follows three simple rules. (i) If the directing influence of both the substituents reinforce each other, a single product results. (ii) If the directing influences of both the substituent groups oppose each other, the most powerful activating group among them has the dominant influence but usually a mixture of products results. (iii) In meta disubstituted compounds, further substitution in between the groups occurs only rarely, due to steric reasons.

To predict:

The major product(s) obtainable from sulfonation of m-dichlorobenzene.

Answer to Problem 51AP

The major product produced during the sulfonation of m-dichlorobenzene is 2,4-dichlorobenzenesulfonicacid.

Explanation of Solution

In electrophilic substitution reactions, Cl is an ortho and para directing and deactivating group. Hence the electrophile, SO₃H⁺, can enter into the ortho and para positions with respect to both Cl atoms. The ortho position in between the two Cl atoms is not favored for steric reasons. Hence the SO₃H gets substituted in the p-position to a Cl which happens to be the ortho position to another Cl to yield 2,4-dichlorobenzenesulfonicacid.

Conclusion

The major product produced during the sulfonation of m-dichlorobenzene is 2,4-dichlorobenzenesulfonicacid(I).

Interpretation Introduction

d)

Interpretation:

The major product(s) obtainable from sulfonation of 2,4-dibromophenol is/are to be predicted.

Concept introduction:

Electrophilic substitution of di and trisubstituted benzenes follows three simple rules. (i) If the directing influence of both the substituents reinforce each other, a single product results. (ii) If the directing influences of both the substituent groups oppose each other, the most powerful activating group among them has the dominant influence but usually a mixture of products results. (iii) In meta disubstituted compounds, further substitution in between the groups occurs only rarely, due to steric reasons.

To predict:

The major product(s) obtainable from sulfonation of 2,4-dibromophenol.

Answer to Problem 51AP

The major product produced during the sulfonation of 2,4-dibromophenol is 3,5-dibromo-2-hydroxybenzenesulfonicacid.

Explanation of Solution

In aromatic electrophilic substitution reactions Br is an ortho and para directing and deactivating group while –OH group also though ortho and para directing is a highly activating group. Hence the –OH group decides the position at which the electrophilic substitution reaction will occur. The electrophile, SO₃H⁺, enters into the ortho and para positions with respect to –OH group. The para position and one ortho position to –OH are blocked by substituents. Hence the SO₃H⁺ enters into the another ortho position to –OH group available to produce 3,5-dibromo-2-hydroxybenzenesulfonicacid.

Conclusion

The major product produced during the sulfonation of 2,4-dibromophenol is 3,5-dibromo-2-hydroxybenzenesulfonicacid.