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AQA A Level Organic Chemistry > 11. Amines > Flashcards

11. Amines Flashcards

1
Q

What are amines?

A

Nitrogen-containing organic compounds

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2
Q

What are amines derived from?

A

Ammonia

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3
Q

What is a primary amine?

A

An ammonia molecule with one of the hydrogen atoms replaced by an alkyl or aryl group

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4
Q

What is a secondary amine?

A

An ammonia molecule with two of the hydrogen atoms replaced by an alkyl or aryl group

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5
Q

What is a tertiary amine?

A

An ammonia molecule with all three of the hydrogen atoms replaced with an alkyl or aryl group

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6
Q

What is an alkyl group?

A

A saturated hydrocarbon side group derived from an alkane

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7
Q

What is an aryl group?

A

An unsaturated hydrocarbon side group derived from an arene

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8
Q

What happens when the lone pair in a tertiary amine is used for bonding?

A

A quaternary ammonium salt is formed

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9
Q

What does it mean, if a molecule is aliphatic?

A

It is not aromatic i.e. it doesn’t have a benzene ring

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10
Q

How can amines be prepared?

A
  • nucleophilic substitution of a halogenoalkane

* reduction from nitriles

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11
Q

How many ways can amines be prepared?

A

2

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12
Q

What products does the preparation of amines from halogenoalkanes result in?

A

A mixture of primary, secondary and tertiary amines and their salts

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13
Q

What products does the preparation of amines from a nitrile result in?

A

Primary amines only

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14
Q

How would amines be prepared, if you wanted to produce primary amines only?

A

Reduction from a nitrile

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15
Q

What are the reactants for production of amines through nucleophilic substitution?

A

A halogenoalkane and excess ammonia

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16
Q

Conditions for the production of amines through nucleophilic substitution?

A

Excess ammonia (dissolved in ethanol) - warmed in a sealed vessel

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17
Q

Why is ethanol used to dissolve the ammonia when producing amines through nucleophilic substitution?

A

As water would protonate the NH3

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18
Q

What does ammonia act as in the nucleophilic substitution to form amines?

A

A nucleophile

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19
Q

How can it be ensured that a primary amine is the main product from nucleophilic substitution?

A

Using excess ammonia

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20
Q

Why is nucleophilic substitution not the most efficient method of producing primary amines?

A

As a mixture of 1°, 2°, 3° amines and 4° salts are formed

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21
Q

Why is a mixture of 1°, 2° and 3° amines, as well as 4° salts, formed in nucleophilic substitution?

A

The primary amine produced can act as a nucleophile to form a secondary amine and so on

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22
Q

How are nitriles reduced to form amines?

A

Using a strong reducing agent e.g. LiAlH₄ in dry ether followed by addition of dilute acid, at room temperature

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23
Q

What reducing agents can be used to form amines?

A

LiAlH₄

OR

Nickel catalyst and hydrogen gas

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24
Q

How many times can you reduce a nitrile?

A

Once

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25
Q

General equation for reduction of a nitrile?

A

R - C ≡ N + 2H₂ → R - CH₂NH₂

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26
Q

Is the mechanism for the reduction of a nitrile required?

A

No - however the mechanism for the production of a nitrile is

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27
Q

What mechanism produces nitriles?

A

Nucleophilic substitution

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28
Q

What are the equations for the two synthetic paths for making butylamine?

A
  1. CH3CH2CH2CH2Cl + 2NH3 → CH3CH2CH2CH2NH2 + NH4⁺ + :Cl⁻

2a. CH3CH2CH2Cl + KCN → CH3CH2CH2CN + KCl
2b. CH3CH2CH2CN + 4[H]→ CH3CH2CH2CH2NH2

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29
Q

Why are aromatic amines important organic reagents?

A

They are used in the manufacture of dyes

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30
Q

Why can’t aromatic amines be produced directly by nucleophilic substitution of chlorobenzene?

A

The yield would be too small - as the electron dense benzene ring would repel the lone pair on the nucleophiles

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31
Q

Why is the yield small in the production of aromatic amines using nucleophilic substitution of chlorobenzene?

A

The electron dense benzene ring would repel the lone pair on the nucleophiles

32
Q

How are aromatic amines produced?

A

The reduction of nitrobenzene

33
Q

What conditions are needed for the production of aromatic amines?

A

For reduction of nitrobenzene → Tin (Sn) and concentrated HCl under reflux

34
Q

What is produced when nitrobenzene is treated with Sn and concentrated HCl under reflux?

35
Q

How is the aromatic amine released from the salt in the reduction of nitrobenzene?

A

By adding NaOH

36
Q

Equations for the reduction of nitrobenzene?

A
  • C6H5NO2 + 6[H] → C6H5NH2 + 2H2O

* C6H5NH3⁺Cl⁻ + NaOH → C6H5NH2 + H2O + NaCl

37
Q

What conditions are needed for the steps to produce aromatic amines from benzene?

A
  1. Benzene → Nitrobenzene [conc. HNO3 and H2SO4 and 50°C]

2. Nitrobenzene → Aromatic amine [a) Tin, conc. HCl and heat and b) NaOH solution]

38
Q

How is nitrobenzene produced?

A

The nitration of benzene

39
Q

Equation for nitration of benzene?

A

C6H6 + HNO3 → C6H5NO2 + H2O

40
Q

What can be used as an alternative catalyst for the reduction of a nitrile to produce a primary aliphatic amine, and the reduction of nitro compounds to produce aromatic amines?

A

Hydrogen gas and nickel catalyst

41
Q

Which reactions can hydrogen gas and nickel catalyse?

A
  • reduction of nitriles → 1° aliphatic amines

* reduction of nitro compounds → aromatic amines

42
Q

What did Bronsted and Lowry define acids as?

A

A proton donor (H⁺)

43
Q

What did Bronsted and Lowry define bases as?

A

A proton acceptor

44
Q

During a reaction between acids and bases, what happens in terms of protons?

A

A proton transfer occurs

45
Q

Why are amines and ammonia Bronsted-Lowry bases?

A

They have a lone pair that can be used to accept a proton

46
Q

Are amines and ammonia Bronsted-Lowry acids or bases?

47
Q

Are amines weak or strong bases?

48
Q

Is ammonia a strong or a weak base?

49
Q

What does the strength of a base (amines) depend on?

A

The availibility of the lone pair on the N atom

50
Q

What does it mean for the strength of a base, if the lone pair is more availible?

A

The stronger the base

51
Q

What does the availibility of a lone pair in amines depend on?

A

How much electron density is on the nitrogen atom, and this depends on the adjacent groups

52
Q

Are alkyl groups electron repelling or attracting?

53
Q

What is the inductive effect in amines?

A

When alkyl groups are electron repelling, pushing electrons towards the nitrogen atom in the amine

54
Q

What is the result of the inductive effect from alkyl groups in amines?

A

The lone pair on the nitrogen is more availible for bonding and therefore a stronger base

55
Q

What effect does the number of alkyl groups bonded to the nitrogen in amines have on the strength of the base?

A

The more alkyl groups, stronger the base

56
Q

Out of ammonia, 1°, 2° and 3° amines, which is the weakest base?

57
Q

Out of ammonia, 1°, 2° and 3° amines, which is the strongest base?

A

3° amines

58
Q

What is an aryl group?

A

Containing a benzene ring

59
Q

What effect do aryl groups have on the strength of (amine) bases?

A
  • they cause the lone pair on the N atom to be delocalised into the benzene ring
  • making it less availible for bonding
  • therefore a weaker base
60
Q

What happens in terms of the strength of an (amine) base when there are more aryl groups bonded to the N atom?

A

The base is weaker

61
Q

Relative base strength of amines from strongest to weakest?

A
  • 3° amine
  • 2° amine
  • 1° amine
  • ammonia
  • pheyl amine
  • diphenyl amine
  • triphenyl amine
62
Q

Which is the stronger base; methylamine or diethylamine?

A

Diethylamine

63
Q

Which is the stronger base; propylamine or phenylamine?

A

Propylamine

64
Q

What can amines act as?

A
  • bases

* nucleophiles

65
Q

As well as bases, what can amines act as?

A

Nucleophiles

66
Q

Can ammonia act as a nucleophile and a base?

67
Q

What happens when amines react with halogenoalkanes?

A

Nucleophilic substitution

68
Q

What is the relative strength of the amine bases the same as?

A

The relative strength of the nucleophiles

69
Q

How is a mixture of 1°, 2° and 3° amines, as well as 4° salts, produced in nucleophilic substitution of halogenoalkanes with ammonia?

A
  • after ammonia reacts to form a 1° amine, this amine has a lone pair which can act as a nucleophile
  • substitution of the halogen for the amine will occur as it is a stronger nucleophile than ammonia
  • repeated substitution takes place
70
Q

What happens if excess ammonia is used in the reaction with halogenoalkanes?

A

The yield of the 1° amine is increased

71
Q

What happens if excess halogenoalkane is used in the reaction with ammonia?

A

The main organic product will be the 4° salt

72
Q

How can quaternary ammonia salts be made?

A
  • by reacting halogenoalkanes and ammonia in a 4:1 ratio

* or by reacting 3° amines and halogenoalkanes in a 1:1 ratio

73
Q

Why 4° salts classed as cationic surfactants?

A

The +ve charge on the N atom makes it attracted to negatively charged surfactants e.g. hair, fabrics

74
Q

Why are 4° salts useful in fabric and hair conditioners?

A

They are cationic surfactants

75
Q

What are the uses of 4° ammonium salts?

A

Fabric and hair conditioners, anti-static agents and emulsifiers

76
Q

How long are the alkyl groups usually in 4° salts?

A

Quite long

AQA A Level Organic Chemistry (16 decks)

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