What is the difference between an aliphatic amine and an aromatic amine ?

In an aliphatic amine , the nitrogen is attached to alkyl groups. In an aromatic amine , the nitrogen is attached to an aryl group (e.g. a benzene ring). Phenylamine (C 6 H 5 NH 2 ) is an example of an aromatic amine.

Primary amines can be prepared by reacting halogenoalkanes with excess hot .......... under .......... . Excess ammonia is used to maximise the .......... .

Primary amines can be prepared by reacting halogenoalkanes with excess hot ethanolic ammonia under pressure . Excess ammonia is used to maximise the primary amine .

True or False? Reduction of a nitrile group (–CN) with LiAlH 4 in dry ether gives a primary amine.

True. The nitrile group is reduced to an –NH 2 group. For example, ethanenitrile (CH 3 CN) is reduced to ethylamine (CH 3 CH 2 NH 2 ). H 2 with a Ni catalyst can also be used.

What is the four-step route from benzene to phenylamine?

Nitration of benzene with conc. HNO 3 /H 2 SO 4 below 55 °C → nitrobenzene Reduction with Sn and conc. HCl under reflux → acidic mixture Addition of NaOH → phenylamine Separation by steam distillation

Without excess ammonia, the reaction of a halogenoalkane with ammonia produces a mixture of .......... , .......... and .......... amines as well as a .......... ammonium salt.

Without excess ammonia, the reaction of a halogenoalkane with ammonia produces a mixture of primary , secondary and tertiary amines as well as a quaternary ammonium salt.

True or False? Aromatic amines prepared by the reduction of nitro compounds are used in the manufacture of dyes.

True. Phenylamine and related aromatic amines are important intermediates in the synthesis of azo dyes.

What is the classification basis for primary, secondary and tertiary amines?

The number of alkyl or aryl groups attached to the nitrogen atom : primary (1 group), secondary (2 groups), tertiary (3 groups). This is different from the classification of alcohols, which is based on the carbon bearing the –OH.

Why do amines act as bases?

The lone pair of electrons on the nitrogen atom can accept a proton (H + ), forming a dative covalent bond. This makes amines Brønsted–Lowry bases.

True or False? Ethylamine is a stronger base than phenylamine.

True. The ethyl group donates electron density to the nitrogen (positive inductive effect), making the lone pair more available to accept a proton. In phenylamine, the lone pair is delocalised into the benzene ring, making it less available.

Amines react with HCl to form .......... salts. For example, ethylamine reacts with HCl to give .......... . These salts are .......... for small R groups.

Amines react with HCl to form amine salts. For example, ethylamine reacts with HCl to give C 2 H 5 NH 3 + Cl - (ethylammonium chloride). These salts are water-soluble for small R groups.

What is the positive inductive effect and how does it affect amine basicity?

The positive inductive effect is the donation of electron density by an alkyl group to the nitrogen atom. This increases the availability of the lone pair, making the amine a stronger base .

Why does the presence of a benzene ring reduce the basicity of phenylamine?

The lone pair on nitrogen is delocalised into the benzene ring , making it less available to accept a proton. This reduces phenylamine's basicity compared to aliphatic amines or ammonia.

In Brønsted–Lowry terms, an amine acts as a .......... acceptor. When ethylamine reacts with HCl, the amine acts as a .......... : N donates its .......... to the proton.

In Brønsted–Lowry terms, an amine acts as a proton acceptor. When ethylamine reacts with HCl, the amine acts as a base : N donates its lone pair to the proton.

True or False? Amine salts are more volatile than the parent amine, which is why adding an acid to an amine removes its fishy smell.

False. Amine salts are less volatile (ionic, non-volatile) than the parent amine. Adding acid converts the volatile amine to a non-volatile salt, which is why the fishy smell disappears.

How does ammonia act as a nucleophile in reactions with halogenoalkanes?

The lone pair on the nitrogen atom attacks the δ+ carbon bearing the halogen, displacing the halide ion. In step 2, ammonia acts as a base, removing an H + to give the primary amine.

The overall equation for the reaction of a halogenoalkane with ammonia to give a primary amine is: RCH 2 X + 2NH 3 → .......... + .......... .

The overall equation for the reaction of a halogenoalkane with ammonia to give a primary amine is: RCH 2 X + 2NH 3 → RCH 2 NH 2 + NH 4 X.

True or False? When a primary amine reacts with more halogenoalkane, further substitution can occur to give secondary and tertiary amines.

True. The primary amine is itself a good nucleophile. Further substitution can give secondary amines, tertiary amines and ultimately quaternary ammonium salts. Excess ammonia is used to limit this.

Why is excess ammonia used when preparing a primary amine from a halogenoalkane?

To ensure ammonia is the dominant nucleophile, limiting further substitution of the primary amine. Without excess, a mixture of primary, secondary and tertiary amines and a quaternary ammonium salt forms.

In the nucleophilic substitution of CH 3 Cl with NH 3 , the first step gives the salt .......... . In the second step, a molecule of .......... removes a proton to give the primary amine .......... and .......... chloride.

In the nucleophilic substitution of CH 3 Cl with NH 3 , the first step gives the salt [CH 3 NH 3 ] + Cl - . In the second step, a molecule of NH 3 removes a proton to give the primary amine CH 3 NH 2 and ammonium chloride.

True or False? In nucleophilic substitution of a halogenoalkane with ammonia, only one mole of ammonia is needed.

False. Two moles of ammonia are needed: the first acts as a nucleophile to attack the carbon, and the second acts as a base to remove H + from the intermediate salt.

Quaternary ammonium salt

A quaternary ammonium salt contains a nitrogen atom bonded to four alkyl groups , giving it a permanent positive charge (NR 4 + ). It forms as the final product when a tertiary amine undergoes a fourth nucleophilic substitution with a halogenoalkane; no further substitution is possible.

What type of product forms when an acyl chloride reacts with ammonia?

A primary amide (e.g. propanamide, CH 3 CH 2 CONH 2 ) plus ammonium chloride (NH 4 Cl), which forms as white fumes from the HCl reacting with excess NH 3 .

In the reaction of an acyl chloride with a primary amine, the .......... on nitrogen attacks the .......... carbon. After addition, .......... is eliminated. The HCl then reacts with excess amine to form an .......... salt.

In the reaction of an acyl chloride with a primary amine, the lone pair on nitrogen attacks the carbonyl carbon. After addition, HCl is eliminated. The HCl then reacts with excess amine to form an organic ammonium salt.

True or False? Acyl chlorides are more reactive than acid anhydrides towards nucleophilic addition–elimination because the C–Cl bond creates a stronger dipole on the carbonyl carbon.

True. Acyl chlorides are more reactive than esters towards nucleophilic addition-elimination. Although oxygen is more electronegative than chlorine, the C–Cl bond is weaker and Cl - is a better leaving group than OR - , making the carbonyl carbon in acyl chlorides more susceptible to nucleophilic attack.

What two formal charges must be shown on the charged intermediate in the mechanism of nucleophilic addition–elimination of an acyl chloride with ammonia?

O - on the oxygen atom and N + on the nitrogen atom. Both must be shown, and the Cl must not leave in the same step as nucleophilic attack.

The overall equation for the reaction of RCOCl with two moles of NH 3 is: RCOCl + 2NH 3 → .......... + .......... .

The overall equation for the reaction of RCOCl with two moles of NH 3 is: RCOCl + 2NH 3 → RCONH 2 + NH 4 Cl.

True or False? In the mechanism of nucleophilic addition–elimination with an acyl chloride, the Cl - ion that is released can remove the H + from the intermediate nitrogen.

False. The Cl - must not be used to remove H + . A second molecule of ammonia or amine acts as the base and removes the H + from the nitrogen in the intermediate.

What is a substituted amide (N-substituted amide)?

A π (pi) bond is a covalent bond formed by the sideways overlap of two parallel p orbitals above and below the plane of the bonded atoms. It is found in double and triple bonds and prevents free rotation about the bond.

What is a quaternary ammonium salt?

A carbocation is a carbon species carrying a positive charge, formed when a bond breaks heterolytically and both electrons are taken by the leaving group. Tertiary carbocations are more stable than secondary, which are more stable than primary.

True or False? Quaternary ammonium salts act as anionic surfactants because their nitrogen carries a negative charge.

False. They are cationic surfactants because the nitrogen carries a positive charge.

In a quaternary ammonium salt used as a fabric softener, the .......... groups are hydrophobic and the .......... amine group is hydrophilic, allowing the molecule to act as a surfactant.

In a quaternary ammonium salt used as a fabric softener, the hydrocarbon (alkyl) groups are hydrophobic and the positively charged amine group is hydrophilic, allowing the molecule to act as a surfactant.

What is a surfactant and how do quaternary ammonium salts function as one?

A surfactant lowers the surface tension between immiscible liquids. Quaternary ammonium salts cluster at water surfaces with their hydrophilic charged heads in the water and their hydrophobic hydrocarbon tails pointing outward.

True or False? Quaternary ammonium salts prevent static build-up on hair and clothing because they are attracted to the negatively charged wet surfaces.

True. Wet hair and fabric acquire negative charges, so the positively charged surfactant is attracted to these surfaces, forming a smooth coating that prevents static.

Quaternary ammonium salts are used as .......... in hair conditioners and as .......... in laundry products to provide a smooth coating and reduce static electricity.

Quaternary ammonium salts are used as cationic surfactants in hair conditioners and as fabric softeners in laundry products to provide a smooth coating and reduce static electricity.

How does the structure of a quaternary ammonium salt differ from that of a primary amine?

In a primary amine, nitrogen is bonded to one alkyl group and retains two N–H bonds. In a quaternary ammonium salt, all four bonds on nitrogen are to alkyl or aryl groups, so there are no N–H bonds and the nitrogen carries a permanent positive charge.

A LevelChemistryAQAFlashcardsAdvanced Organic ChemistryAmines

Amines (AQA A Level Chemistry): Flashcards

Exam code: 7405

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FrontPreparation of Amines
What is the difference between an aliphatic amine and an aromatic amine?

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Cards in this collection (35)

What is the difference between an aliphatic amine and an aromatic amine?
In an aliphatic amine, the nitrogen is attached to alkyl groups. In an aromatic amine, the nitrogen is attached to an aryl group (e.g. a benzene ring). Phenylamine (C₆H₅NH₂) is an example of an aromatic amine.
Primary amines can be prepared by reacting halogenoalkanes with excess hot .......... under .......... . Excess ammonia is used to maximise the .......... .
Primary amines can be prepared by reacting halogenoalkanes with excess hot ethanolic ammonia under pressure. Excess ammonia is used to maximise the primary amine.
True or False?
Reduction of a nitrile group (–CN) with LiAlH₄ in dry ether gives a primary amine.
True.
The nitrile group is reduced to an –NH₂ group. For example, ethanenitrile (CH₃CN) is reduced to ethylamine (CH₃CH₂NH₂). H₂ with a Ni catalyst can also be used.
What is the four-step route from benzene to phenylamine?
1. Nitration of benzene with conc. HNO₃/H₂SO₄ below 55 °C → nitrobenzene
2. Reduction with Sn and conc. HCl under reflux → acidic mixture
3. Addition of NaOH → phenylamine
4. Separation by steam distillation
Without excess ammonia, the reaction of a halogenoalkane with ammonia produces a mixture of .......... , .......... and .......... amines as well as a .......... ammonium salt.
Without excess ammonia, the reaction of a halogenoalkane with ammonia produces a mixture of primary, secondary and tertiary amines as well as a quaternary ammonium salt.
True or False?
Aromatic amines prepared by the reduction of nitro compounds are used in the manufacture of dyes.
True.
Phenylamine and related aromatic amines are important intermediates in the synthesis of azo dyes.
What is the classification basis for primary, secondary and tertiary amines?
The number of alkyl or aryl groups attached to the nitrogen atom: primary (1 group), secondary (2 groups), tertiary (3 groups). This is different from the classification of alcohols, which is based on the carbon bearing the –OH.
Why do amines act as bases?
The lone pair of electrons on the nitrogen atom can accept a proton (H⁺), forming a dative covalent bond. This makes amines Brønsted–Lowry bases.
True or False?
Ethylamine is a stronger base than phenylamine.
True.
The ethyl group donates electron density to the nitrogen (positive inductive effect), making the lone pair more available to accept a proton. In phenylamine, the lone pair is delocalised into the benzene ring, making it less available.
Amines react with HCl to form .......... salts. For example, ethylamine reacts with HCl to give .......... . These salts are .......... for small R groups.
Amines react with HCl to form amine salts. For example, ethylamine reacts with HCl to give C₂H₅NH₃⁺Cl^- (ethylammonium chloride). These salts are water-soluble for small R groups.
What is the positive inductive effect and how does it affect amine basicity?
The positive inductive effect is the donation of electron density by an alkyl group to the nitrogen atom. This increases the availability of the lone pair, making the amine a stronger base.
Why does the presence of a benzene ring reduce the basicity of phenylamine?
The lone pair on nitrogen is delocalised into the benzene ring, making it less available to accept a proton. This reduces phenylamine's basicity compared to aliphatic amines or ammonia.
In Brønsted–Lowry terms, an amine acts as a .......... acceptor. When ethylamine reacts with HCl, the amine acts as a .......... : N donates its .......... to the proton.
In Brønsted–Lowry terms, an amine acts as a proton acceptor. When ethylamine reacts with HCl, the amine acts as a base: N donates its lone pair to the proton.
True or False?
Amine salts are more volatile than the parent amine, which is why adding an acid to an amine removes its fishy smell.
False.
Amine salts are less volatile (ionic, non-volatile) than the parent amine. Adding acid converts the volatile amine to a non-volatile salt, which is why the fishy smell disappears.
How does ammonia act as a nucleophile in reactions with halogenoalkanes?
The lone pair on the nitrogen atom attacks the δ+ carbon bearing the halogen, displacing the halide ion. In step 2, ammonia acts as a base, removing an H⁺ to give the primary amine.
The overall equation for the reaction of a halogenoalkane with ammonia to give a primary amine is: RCH₂X + 2NH₃ → .......... + .......... .
The overall equation for the reaction of a halogenoalkane with ammonia to give a primary amine is: RCH₂X + 2NH₃ → RCH₂NH₂ + NH₄X.
True or False?
When a primary amine reacts with more halogenoalkane, further substitution can occur to give secondary and tertiary amines.
True.
The primary amine is itself a good nucleophile. Further substitution can give secondary amines, tertiary amines and ultimately quaternary ammonium salts. Excess ammonia is used to limit this.
Why is excess ammonia used when preparing a primary amine from a halogenoalkane?
To ensure ammonia is the dominant nucleophile, limiting further substitution of the primary amine. Without excess, a mixture of primary, secondary and tertiary amines and a quaternary ammonium salt forms.
In the nucleophilic substitution of CH₃Cl with NH₃, the first step gives the salt .......... . In the second step, a molecule of .......... removes a proton to give the primary amine .......... and .......... chloride.
In the nucleophilic substitution of CH₃Cl with NH₃, the first step gives the salt [CH₃NH₃]⁺Cl^-. In the second step, a molecule of NH₃ removes a proton to give the primary amine CH₃NH₂ and ammonium chloride.
True or False?
In nucleophilic substitution of a halogenoalkane with ammonia, only one mole of ammonia is needed.
False.
Two moles of ammonia are needed: the first acts as a nucleophile to attack the carbon, and the second acts as a base to remove H⁺ from the intermediate salt.
Quaternary ammonium salt
A quaternary ammonium salt contains a nitrogen atom bonded to four alkyl groups, giving it a permanent positive charge (NR₄⁺). It forms as the final product when a tertiary amine undergoes a fourth nucleophilic substitution with a halogenoalkane; no further substitution is possible.
What type of product forms when an acyl chloride reacts with ammonia?
A primary amide (e.g. propanamide, CH₃CH₂CONH₂) plus ammonium chloride (NH₄Cl), which forms as white fumes from the HCl reacting with excess NH₃.
In the reaction of an acyl chloride with a primary amine, the .......... on nitrogen attacks the .......... carbon. After addition, .......... is eliminated. The HCl then reacts with excess amine to form an .......... salt.
In the reaction of an acyl chloride with a primary amine, the lone pair on nitrogen attacks the carbonyl carbon. After addition, HCl is eliminated. The HCl then reacts with excess amine to form an organic ammonium salt.
True or False?
Acyl chlorides are more reactive than acid anhydrides towards nucleophilic addition–elimination because the C–Cl bond creates a stronger dipole on the carbonyl carbon.
True.
Acyl chlorides are more reactive than esters towards nucleophilic addition-elimination. Although oxygen is more electronegative than chlorine, the C–Cl bond is weaker and Cl^- is a better leaving group than OR^-, making the carbonyl carbon in acyl chlorides more susceptible to nucleophilic attack.
What two formal charges must be shown on the charged intermediate in the mechanism of nucleophilic addition–elimination of an acyl chloride with ammonia?
O^- on the oxygen atom and N⁺ on the nitrogen atom. Both must be shown, and the Cl must not leave in the same step as nucleophilic attack.
The overall equation for the reaction of RCOCl with two moles of NH₃ is: RCOCl + 2NH₃ → .......... + .......... .
The overall equation for the reaction of RCOCl with two moles of NH₃ is: RCOCl + 2NH₃ → RCONH₂ + NH₄Cl.
True or False?
In the mechanism of nucleophilic addition–elimination with an acyl chloride, the Cl^- ion that is released can remove the H⁺ from the intermediate nitrogen.
False.
The Cl^- must not be used to remove H⁺. A second molecule of ammonia or amine acts as the base and removes the H⁺ from the nitrogen in the intermediate.
What is a substituted amide (N-substituted amide)?
A π (pi) bond is a covalent bond formed by the sideways overlap of two parallel p orbitals above and below the plane of the bonded atoms. It is found in double and triple bonds and prevents free rotation about the bond.
What is a quaternary ammonium salt?
A carbocation is a carbon species carrying a positive charge, formed when a bond breaks heterolytically and both electrons are taken by the leaving group. Tertiary carbocations are more stable than secondary, which are more stable than primary.
True or False?
Quaternary ammonium salts act as anionic surfactants because their nitrogen carries a negative charge.
False.
They are cationic surfactants because the nitrogen carries a positive charge.
In a quaternary ammonium salt used as a fabric softener, the .......... groups are hydrophobic and the .......... amine group is hydrophilic, allowing the molecule to act as a surfactant.
In a quaternary ammonium salt used as a fabric softener, the hydrocarbon (alkyl) groups are hydrophobic and the positively charged amine group is hydrophilic, allowing the molecule to act as a surfactant.
What is a surfactant and how do quaternary ammonium salts function as one?
A surfactant lowers the surface tension between immiscible liquids.
Quaternary ammonium salts cluster at water surfaces with their hydrophilic charged heads in the water and their hydrophobic hydrocarbon tails pointing outward.
True or False?
Quaternary ammonium salts prevent static build-up on hair and clothing because they are attracted to the negatively charged wet surfaces.
True.
Wet hair and fabric acquire negative charges, so the positively charged surfactant is attracted to these surfaces, forming a smooth coating that prevents static.
Quaternary ammonium salts are used as .......... in hair conditioners and as .......... in laundry products to provide a smooth coating and reduce static electricity.
Quaternary ammonium salts are used as cationic surfactants in hair conditioners and as fabric softeners in laundry products to provide a smooth coating and reduce static electricity.
How does the structure of a quaternary ammonium salt differ from that of a primary amine?
In a primary amine, nitrogen is bonded to one alkyl group and retains two N–H bonds.
In a quaternary ammonium salt, all four bonds on nitrogen are to alkyl or aryl groups, so there are no N–H bonds and the nitrogen carries a permanent positive charge.

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