Nitration and Sulfonation of Benzene

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Questions and Answers

What is the electrophile produced during the nitration of benzene?

Nitronium ion (NO2+) (correct)

Nitric oxide (NO)

Ammonium ion (NH4+)

Hydronium ion (H3O+)

Which acids are used in the nitration of benzene?

Sulfuric acid and phosphoric acid

Nitric acid and sulfuric acid (correct)

Nitrous acid and hydrochloric acid

Hydrochloric acid and acetic acid

What is the product when a nitro group (NO2) is reduced using Zn, Sn, or Fe in aqueous HCl?

Nitrile (RCN)

Alkyl-substituted product (RNH2)

Amino-substituted product (ArNH2) (correct)

Phenol (C6H5OH)

What is the role of sulfuric acid in the nitration of benzene?

As a catalyst for the reaction Signup and view all the answers

What is the main group produced during the sulfonation of benzene?

Sulfonic acid (—SO3H) Signup and view all the answers

Which mixture is used for sulfonation of benzene?

7% mixture of SO3 and H2SO4 Signup and view all the answers

Which of the following is true regarding the nitration of aromatic rings?

It can produce several different products depending on conditions Signup and view all the answers

What by-product is formed from the reduction of a nitro group in aromatic compounds?

Water (H2O) Signup and view all the answers

What effect do activating substituents have on an aromatic ring?

They increase the ring's reactivity compared to benzene. Signup and view all the answers

Which substituent would make an aromatic ring significantly less reactive than benzene?

NO2 group Signup and view all the answers

In electrophilic aromatic substitution, an OH group directs substitution primarily towards which positions?

Ortho and para positions. Signup and view all the answers

What is the primary outcome when two activating substituents are present on an aromatic ring?

They enhance each other's activating effect. Signup and view all the answers

What is a characteristic outcome when substituents conflict in their directing effects on an aromatic ring?

A mixture of products may result. Signup and view all the answers

What is the role of amalgamated zinc in the Clemmensen reduction process?

It reduces acylbenzenes to alkylbenzenes. Signup and view all the answers

What impact do deactivating substituents generally have on the reactivity of an aromatic ring?

They decrease the ring's reactivity compared to benzene. Signup and view all the answers

Which pair of substituents are observed to have a cumulative deactivating effect on an aromatic ring?

Nitro and Carboxylic groups. Signup and view all the answers

Which type of substituents are ortho and para-directing?

All activating groups Signup and view all the answers

When multiple substituents on a benzene ring direct effects oppose each other, which has the dominant influence?

The most powerful activating group Signup and view all the answers

What happens to alkyl groups attached to an aromatic ring when oxidized?

They are converted into carboxyl groups Signup and view all the answers

Which statement is true about the nitration of toluene compared to benzene?

Toluene is a stronger activator than benzene Signup and view all the answers

What is the expected product distribution when toluene undergoes electrophilic substitution?

More ortho and para substituted products Signup and view all the answers

Which of the following groups is considered deactivating but ortho- and para-directing?

Halogens Signup and view all the answers

If an aromatic compound has an alkyl group as a substituent, how does this group influence substitution reactions?

It is an activating group and ortho, para-director Signup and view all the answers

What is the primary product of the oxidation of ethylbenzene using strong oxidizing agents?

Benzoic acid Signup and view all the answers

What is the main purpose of the Friedel–Crafts alkylation reaction?

To introduce an alkyl group onto an aromatic ring Signup and view all the answers

What role does aluminum chloride (AlCl3) play in the Friedel–Crafts reactions?

It acts as a catalyst to facilitate the dissociation of alkyl halides Signup and view all the answers

Why do Friedel–Crafts reactions fail on aromatic rings that are strongly deactivated?

The presence of strong electron-withdrawing groups reduces reactivity Signup and view all the answers

Which type of product mixture primarily results from the nitration of toluene?

A mixture of ortho and para substituted molecules Signup and view all the answers

What happens during the desulfonation reaction?

A sulfonic acid group is removed from an aromatic ring Signup and view all the answers

What is a common method for carrying out desulfonation reactions effectively?

Utilizing steam as a source of heat and water Signup and view all the answers

During the Friedel-Crafts acylation reaction, what is introduced onto the aromatic ring?

An acyl group Signup and view all the answers

How does the reactivity of toluene compare to that of benzene in electrophilic aromatic substitution?

Toluene reacts 25 times faster than benzene Signup and view all the answers

Which statement about the inductive effect and alkyl groups is true?

Alkyl groups stabilize the carbocation by donating electron density. Signup and view all the answers

What is the role of Lewis acids in electrophilic aromatic substitution?

They increase the reactivity of electrophiles by making them more electron-poor. Signup and view all the answers

In nucleophilic aromatic substitution (NAS), which condition favors the reaction?

Electron-poor aromatic rings and strong nucleophiles. Signup and view all the answers

What is a key difference between electrophilic aromatic substitution (EAS) and nucleophilic aromatic substitution (NAS)?

In NAS, the aromatic ring acts as an electrophile and the attacking species is a nucleophile. Signup and view all the answers

How does the presence of electron-withdrawing groups (EWGs) affect NAS?

They speed up the reaction by increasing the electron deficiency of the ring. Signup and view all the answers

Which position of the aromatic ring is affected by the presence of the leaving group in NAS?

The position of the leaving group determines where the nucleophile will attach. Signup and view all the answers

What role does the carbocation intermediate play in electrophilic aromatic substitution?

It is the rate-determining step of the reaction. Signup and view all the answers

Why is nucleophilic aromatic substitution more favorable in the presence of good nucleophiles?

They can easily form stable intermediates. Signup and view all the answers

Study Notes

Nitration of Benzene

Reaction of aromatic rings with concentrated nitric acid (HNO3) and sulfuric acid (H2SO4) produces the nitronium ion (NO2+), the electrophile.
Sulfuric acid serves as a catalyst, enhancing reaction speed and allowing for lower temperature conditions.
Example: Nitration leads to amino-substituted products, essential for dye and pharmaceutical synthesis.

Reduction of the Nitro Group

Nitro groups (NO2) can be reduced to amino groups (NH2) using metals like zinc, tin, or iron in the presence of aqueous hydrochloric acid (HCl).
Aromatic nitration is primarily conducted in labs, not naturally occurring.

Sulfonation of Benzene

Aromatic rings undergo sulfonation via fuming sulfuric acid, which contains approximately 7% SO3 mixed with H2SO4.
The electrophile in this reaction is HSO3, and it introduces a sulfonic acid group (—SO3H) to the aromatic system.
This process is crucial for synthesizing antibiotics from the sulfa drug family.

Desulfonation Reaction

Sulfonic acid groups can be removed by heating with dilute sulfuric acid, often with steam providing both heat and water.

Nitration of Toluene

Toluene nitrates 25 times faster than benzene due to the activating effect of the methyl group.
The primary products formed are ortho and para substituted derivatives.

Friedel–Crafts Alkylation and Acylation

Friedel–Crafts alkylation involves adding an alkyl group (R) to benzene through alkyl chloride and aluminum chloride (AlCl3) as a catalyst.
Friedel–Crafts acylation introduces an acyl group (R-C=O) via the reaction of aromatic compounds with acyl chloride (RCOCl) and AlCl3.
Example: Benzene reacts with acetyl chloride to produce acetophenone.

Limitations of Friedel–Crafts

Effective on benzene and its activated derivatives, but fails on strongly deactivated aromatic rings (NO2, CN, SO3H, COR).
Carbocation rearrangements may occur, and alkylbenzene products can lead to multiple substitutions (polyalkylation).

Clemmensen Reduction

Converts acylbenzenes to alkylbenzenes using aqueous HCl and amalgamated zinc.

Substituent Effects in Electrophilic Aromatic Substitution

Substituents can either activate or deactivate aromatic rings, affecting reactivity compared to benzene.
Significant reactivity differences: -OH makes a ring 1000 times more reactive, while -NO2 makes it over 10 million times less reactive.
Substituents affect reaction orientation; ortho and para positions favored with activating groups, while meta positions favored with deactivating groups.

Effects of Multiple Substituents

Combined effects dictate reactivity. Activating groups typically dominate over deactivating groups.
Activators direct substitutions to ortho and para positions; deactivators generally direct to meta positions, except halogens which are ortho/para directing.

Oxidation and Reduction of Aromatic Compounds

Benzene typically does not react with strong oxidizing agents like KMnO4; however, alkyl groups can be oxidized to carboxylic acids (CO2H).
Example: Ethylbenzene oxidized to benzoic acid.

Alkyl Group Stabilization

Alkyl groups act as activating substituents and direct to ortho/para positions via inductive effects, enhancing electron density on the ring.

Review of Electrophilic Aromatic Substitution (EAS)

The aromatic ring acts as a nucleophile that attacks an electrophile, forming a carbocation intermediate.
Electron-donating groups (like -OH and alkyl groups) increase reaction speed by stabilizing the carbocation, while electron-withdrawing groups (like -NO2 and -SO3H) slow it down.

Nucleophilic Aromatic Substitution (NAS)

NAS features a nucleophile attacking an electron-poor aromatic ring (instead of an electrophile in EAS).
The reaction rates increase with electron-withdrawing groups, which stabilize the intermediate formed during substitution.
The position of nucleophile attack is determined by the leaving group, contrasting with the multiple orientations in EAS.

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Description

This quiz covers the nitration and sulfonation processes of benzene, including the formation of important electrophiles and the reduction of nitro groups. Understand the role of catalysts and reactions that are pivotal for dye and pharmaceutical synthesis. Perfect for students of organic chemistry.