A phenylamine is an organic compound consisting of a benzene ring with an -NH 2 functional group. It is prepared from benzene via nitration, reduction and deprotonation.

What are the three main steps in the preparation of phenylamine from benzene?

Nitration of benzene using concentrated HNO 3 and H 2 SO 4 at 25–60 °C to form nitrobenzene. Reduction of nitrobenzene with hot tin (Sn) and concentrated HCl under reflux. Deprotonation with NaOH to form phenylamine.

True or False? Phenylamine reacts with bromine water at room temperature to form 2,4,6-tribromophenylamine.

True. The lone pair on nitrogen donates electron density into the benzene ring, activating it toward electrophilic substitution. Bromination occurs at the 2, 4 and 6 positions under mild conditions.

How is phenylamine separated from the reaction mixture after its synthesis?

Phenylamine is separated by steam distillation , which allows it to be distilled from the mixture at a temperature below its boiling point.

In the reaction of phenylamine with nitrous acid below 10 °C, a .......... salt is formed. On warming with water, this decomposes to form .......... .

In the reaction of phenylamine with nitrous acid below 10 °C, a diazonium salt is formed. On warming with water, this decomposes to form phenol .

Why must the temperature be kept below 10 °C during the formation of the diazonium salt from phenylamine?

The diazonium salt is unstable and will thermally decompose to phenol, nitrogen and HCl at higher temperatures. Keeping the mixture below 10 °C prevents decomposition.

True or False? Nitrous acid must be prepared in situ because it is too unstable to store.

True. Nitrous acid (HNO 2 ) is so unstable that it is prepared in the test tube by reacting sodium nitrite (NaNO 2 ) with dilute HCl, kept below 10 °C using ice.

Define diazotisation .

A diazotisation is the reaction between nitrous acid and phenylamine at below 10 °C to form a diazonium ion (containing an -N 2 + group).

Phenylamine reacts with electrophiles at the .......... positions of the benzene ring. This is because the nitrogen lone pair .......... electron density into the ring.

Phenylamine reacts with electrophiles at the 2, 4 and 6 positions of the benzene ring. This is because the nitrogen lone pair donates electron density into the ring.

What is the order of basicity of ethylamine, ammonia and phenylamine, from strongest to weakest?

Ethylamine > ammonia > phenylamine. The ethyl group donates electron density to nitrogen (increasing basicity). Ammonia has no such group. The benzene ring in phenylamine delocalises the lone pair (decreasing basicity).

True or False? Ammonia is a stronger base than ethylamine because it has no substituents on the nitrogen atom.

False. Ethylamine is a stronger base than ammonia. The ethyl group donates electron density to nitrogen via the positive inductive effect, making the lone pair more available for dative bonding with a proton.

Define dative covalent bond .

A dative covalent bond is a covalent bond in which both electrons are donated by one atom. In base chemistry, the nitrogen lone pair is donated to a proton (H + ) to form this bond.

Why is phenylamine the weakest base of the three species: ethylamine, ammonia and phenylamine?

In phenylamine, the lone pair on nitrogen overlaps with the conjugated pi system of the benzene ring and becomes delocalised. This makes the lone pair less available for dative covalent bonding with a proton.

Electron- .......... groups increase the basicity of an amine by making the lone pair on nitrogen more available. Electron- .......... groups decrease basicity.

Electron- donating groups increase the basicity of an amine by making the lone pair on nitrogen more available. Electron- withdrawing groups decrease basicity.

True or False? The lone pair on nitrogen in ethylamine is more available for proton bonding than in ammonia.

True. The ethyl group in ethylamine has a positive inductive effect, donating electron density to nitrogen. This increases the availability of the lone pair and makes ethylamine a stronger base than ammonia.

What structural feature of phenylamine causes its lone pair to be less available for bonding?

The lone pair on the nitrogen atom in phenylamine overlaps with the pi electrons of the benzene ring. This delocalisation spreads the lone pair across the ring, reducing its availability for dative bond formation.

In phenylamine, the lone pair on nitrogen becomes .......... into the benzene ring. Ammonia lacks an electron-donating group and so is less basic than .......... but more basic than phenylamine.

In phenylamine, the lone pair on nitrogen becomes delocalised into the benzene ring. Ammonia lacks an electron-donating group and so is less basic than ethylamine but more basic than phenylamine.

Define delocalisation (in amines) .

A delocalisation (in amines) is the spreading of the nitrogen lone pair into the pi system of an aromatic ring, reducing its availability for dative covalent bonding and decreasing basicity.

Define azo compound .

An azo compound is an organic compound containing the R 1 -N=N-R 2 group, often used as dyes due to the extended delocalisation across the two aromatic rings.

What are the three steps used to make an azo dye from phenylamine?

Form nitrous acid (HNO 2 ) from NaNO 2 and dilute HCl below 10 °C. Diazotisation : react phenylamine with HNO 2 to form benzenediazonium chloride below 10 °C. Coupling reaction : react the diazonium ion with alkaline phenol.

True or False? The diazonium ion acts as a nucleophile in the coupling reaction with phenol.

False. The diazonium ion acts as an electrophile . It undergoes electrophilic substitution into the benzene ring of phenol at the 4th position.

Why are azo compounds very stable?

The -N=N- group acts as a bridge between two benzene rings. The pi electrons from both rings are delocalised through the azo group, creating an extended conjugated system that gives the compound stability.

In the coupling reaction, the diazonium ion substitutes into the .......... position of the phenol ring. .......... conditions are required to deprotonate the product and form the azo compound.

In the coupling reaction, the diazonium ion substitutes into the 4th position of the phenol ring. Alkaline conditions are required to deprotonate the product and form the azo compound.

True or False? Benzenediazonium chloride is stable at room temperature.

False. Benzenediazonium chloride is unstable and must be kept below 10 °C using ice. At higher temperatures it decomposes to phenol, nitrogen gas and HCl.

What is the role of alkaline conditions in the coupling reaction between a diazonium salt and phenol?

Alkaline conditions deprotonate the phenol (and the intermediate product), producing the azo compound as the final product. The base removes an H + from the organic product to form the coloured azo dye.

Define coupling reaction .

A coupling reaction is the electrophilic substitution of a diazonium ion into an activated aromatic ring (such as phenol or dimethylaniline) to form an azo compound.

Nitrous acid is prepared by reacting .......... with dilute hydrochloric acid. The temperature must be kept below .......... °C to prevent decomposition.

Nitrous acid is prepared by reacting sodium nitrite (NaNO 2 ) with dilute hydrochloric acid. The temperature must be kept below 10 °C to prevent decomposition.

A LevelChemistryCambridge (CIE)Flashcards34. Nitrogen CompoundsPhenylamine & Azo Compounds

Phenylamine & Azo Compounds (Cambridge (CIE) A Level Chemistry): Flashcards

Exam code: 9701

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FrontProduction & Reactions of Phenylamine
Define phenylamine.
FrontProduction & Reactions of Phenylamine
What are the three main steps in the preparation of phenylamine from benzene?
BackProduction & Reactions of Phenylamine
Nitration of benzene using concentrated HNO₃ and H₂SO₄ at 25–60 °C to form nitrobenzene.
Reduction of nitrobenzene with hot tin (Sn) and concentrated HCl under reflux.
Deprotonation with NaOH to form phenylamine.

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Cards in this collection (27)

Define phenylamine.
A phenylamine is an organic compound consisting of a benzene ring with an -NH₂ functional group. It is prepared from benzene via nitration, reduction and deprotonation.
What are the three main steps in the preparation of phenylamine from benzene?
1. Nitration of benzene using concentrated HNO₃ and H₂SO₄ at 25–60 °C to form nitrobenzene.
2. Reduction of nitrobenzene with hot tin (Sn) and concentrated HCl under reflux.
3. Deprotonation with NaOH to form phenylamine.
True or False?
Phenylamine reacts with bromine water at room temperature to form 2,4,6-tribromophenylamine.
True.
The lone pair on nitrogen donates electron density into the benzene ring, activating it toward electrophilic substitution. Bromination occurs at the 2, 4 and 6 positions under mild conditions.
How is phenylamine separated from the reaction mixture after its synthesis?
Phenylamine is separated by steam distillation, which allows it to be distilled from the mixture at a temperature below its boiling point.
In the reaction of phenylamine with nitrous acid below 10 °C, a .......... salt is formed. On warming with water, this decomposes to form .......... .
In the reaction of phenylamine with nitrous acid below 10 °C, a diazonium salt is formed. On warming with water, this decomposes to form phenol.
Why must the temperature be kept below 10 °C during the formation of the diazonium salt from phenylamine?
The diazonium salt is unstable and will thermally decompose to phenol, nitrogen and HCl at higher temperatures. Keeping the mixture below 10 °C prevents decomposition.
True or False?
Nitrous acid must be prepared in situ because it is too unstable to store.
True.
Nitrous acid (HNO₂) is so unstable that it is prepared in the test tube by reacting sodium nitrite (NaNO₂) with dilute HCl, kept below 10 °C using ice.
Define diazotisation.
A diazotisation is the reaction between nitrous acid and phenylamine at below 10 °C to form a diazonium ion (containing an -N₂⁺ group).
Phenylamine reacts with electrophiles at the .......... positions of the benzene ring. This is because the nitrogen lone pair .......... electron density into the ring.
Phenylamine reacts with electrophiles at the 2, 4 and 6 positions of the benzene ring. This is because the nitrogen lone pair donates electron density into the ring.
What is the order of basicity of ethylamine, ammonia and phenylamine, from strongest to weakest?
Ethylamine > ammonia > phenylamine.
The ethyl group donates electron density to nitrogen (increasing basicity). Ammonia has no such group. The benzene ring in phenylamine delocalises the lone pair (decreasing basicity).
True or False?
Ammonia is a stronger base than ethylamine because it has no substituents on the nitrogen atom.
False.
Ethylamine is a stronger base than ammonia. The ethyl group donates electron density to nitrogen via the positive inductive effect, making the lone pair more available for dative bonding with a proton.
Define dative covalent bond.
A dative covalent bond is a covalent bond in which both electrons are donated by one atom. In base chemistry, the nitrogen lone pair is donated to a proton (H⁺) to form this bond.
Why is phenylamine the weakest base of the three species: ethylamine, ammonia and phenylamine?
In phenylamine, the lone pair on nitrogen overlaps with the conjugated pi system of the benzene ring and becomes delocalised. This makes the lone pair less available for dative covalent bonding with a proton.
Electron-.......... groups increase the basicity of an amine by making the lone pair on nitrogen more available. Electron-.......... groups decrease basicity.
Electron-donating groups increase the basicity of an amine by making the lone pair on nitrogen more available. Electron-withdrawing groups decrease basicity.
True or False?
The lone pair on nitrogen in ethylamine is more available for proton bonding than in ammonia.
True.
The ethyl group in ethylamine has a positive inductive effect, donating electron density to nitrogen. This increases the availability of the lone pair and makes ethylamine a stronger base than ammonia.
What structural feature of phenylamine causes its lone pair to be less available for bonding?
The lone pair on the nitrogen atom in phenylamine overlaps with the pi electrons of the benzene ring. This delocalisation spreads the lone pair across the ring, reducing its availability for dative bond formation.
In phenylamine, the lone pair on nitrogen becomes .......... into the benzene ring. Ammonia lacks an electron-donating group and so is less basic than .......... but more basic than phenylamine.
In phenylamine, the lone pair on nitrogen becomes delocalised into the benzene ring. Ammonia lacks an electron-donating group and so is less basic than ethylamine but more basic than phenylamine.
Define delocalisation (in amines).
A delocalisation (in amines) is the spreading of the nitrogen lone pair into the pi system of an aromatic ring, reducing its availability for dative covalent bonding and decreasing basicity.
Define azo compound.
An azo compound is an organic compound containing the R₁-N=N-R₂ group, often used as dyes due to the extended delocalisation across the two aromatic rings.
What are the three steps used to make an azo dye from phenylamine?
1. Form nitrous acid (HNO₂) from NaNO₂ and dilute HCl below 10 °C.
2. Diazotisation: react phenylamine with HNO₂ to form benzenediazonium chloride below 10 °C.
3. Coupling reaction: react the diazonium ion with alkaline phenol.
True or False?
The diazonium ion acts as a nucleophile in the coupling reaction with phenol.
False.
The diazonium ion acts as an electrophile. It undergoes electrophilic substitution into the benzene ring of phenol at the 4th position.
Why are azo compounds very stable?
The -N=N- group acts as a bridge between two benzene rings. The pi electrons from both rings are delocalised through the azo group, creating an extended conjugated system that gives the compound stability.
In the coupling reaction, the diazonium ion substitutes into the .......... position of the phenol ring. .......... conditions are required to deprotonate the product and form the azo compound.
In the coupling reaction, the diazonium ion substitutes into the 4th position of the phenol ring. Alkaline conditions are required to deprotonate the product and form the azo compound.
True or False?
Benzenediazonium chloride is stable at room temperature.
False.
Benzenediazonium chloride is unstable and must be kept below 10 °C using ice. At higher temperatures it decomposes to phenol, nitrogen gas and HCl.
What is the role of alkaline conditions in the coupling reaction between a diazonium salt and phenol?
Alkaline conditions deprotonate the phenol (and the intermediate product), producing the azo compound as the final product. The base removes an H⁺ from the organic product to form the coloured azo dye.
Define coupling reaction.
A coupling reaction is the electrophilic substitution of a diazonium ion into an activated aromatic ring (such as phenol or dimethylaniline) to form an azo compound.
Nitrous acid is prepared by reacting .......... with dilute hydrochloric acid. The temperature must be kept below .......... °C to prevent decomposition.
Nitrous acid is prepared by reacting sodium nitrite (NaNO₂) with dilute hydrochloric acid. The temperature must be kept below 10 °C to prevent decomposition.

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