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A Level Chemistry > Module 6 Section 2: Nitrogen Compounds, Polymers and Synthesis > Flashcards

Module 6 Section 2: Nitrogen Compounds, Polymers and Synthesis Flashcards

1
Q

How can polymers be formed

A

Alkenes can form polymers by addition polymerisation or condensation polymerisation

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2
Q

What are two condensation polymers

A

Polyesters and polyamides

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3
Q

Where polyesters and polyamides originate from

A

Carboxylic acids and their derivatives are common starting materials

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4
Q

What is condensation polymerisation

A

The joining of monomers with loss of a small molecule
The small molecule usually includes water or hydrogen chloride
Two different functional groups are needed

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5
Q

How are monomers joined together in polyesters

A

Joined together by ester bonds (esterification) in a long chain to form a polymer

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6
Q

What do the monomers contain in polyesters

A

One monomer containing both a carboxylic acid and an alcohol group
Or from two monomers - one containing two carboxylic acid groups (dicarboxylic) and the other containing two alcohol groups (diol)

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7
Q

Example of a polyester formed from a monomer with two different functional groups

A

Glycolic acid contains both a hydroxyl group and a carboxyl group
It undergoes condensation polymerisation to form poly(glycolic acid) joined by ester linkages and water is released

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8
Q

Example of a polyester formed from two monomers each containing two functional groups

A

Terylene (polyethylene terephthalate or PET) is formed from the reaction between two monomers, benzene-1,4-carboxylic acid and ethane-1,2-diol
During the reaction a hydroxyl group on the diol reacts with a carboxyl group on the dicarboxylic acid forming an ester linkage and water

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9
Q

What are polyamides

A

Formed when monomers are joined by amide linkages in a long chain to form a polymer

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10
Q

What do the monomers contain in polyamides

A

Polyamides can be made from one monomer containing both a carboxylic acid (or acyl chloride) and an amine group
Or from two monomers, one containing two carboxylic acid groups (or acyl chlorides) (dicarboxylic acid) and the other containing two amine groups (diamine)

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11
Q

Example of a polyamide formed from one monomer with two functional groups

A

Amino acids contain both an amine group and a carboxylic acid group
Amino acids undergo condensation polymerisation to form polypeptides or proteins

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12
Q

What happens when an amide bond is formed

A

When an amide bond is formed the carboxyl group reacts with the amine group to form an amide linkage and water is lost (hydroxyl in COOH reacts with hydrogen in NH2)

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13
Q

Example of a polyamide formed from two monomers each with two functional groups

A

Nylon is formed from hexanedioic acid and 1,6-diaminohexane or hexanedioyl chloride and 1,6-diaminohexane
Different types of nylon can be made by varying the carbon chain length

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14
Q

How can polyesters and polyamides be hydrolysed

A

Can be hydrolysed using hot aqueous alkali such as sodium hydroxide
Or by hot aqueous acid such as hydrochloric acid

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15
Q

What do polyesters form when they are hydrolysed

A

They form a metal salt of the carboxylic acid (e.g. a dicarboxylic acid salt) and a diol

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16
Q

What do polyamides form when they are hydrolysed

A

They form a dicarboxylic acid and a diamine

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17
Q

How are polyesters and polyamides more easily hydrolysed

A

Polyamides are more easily hydrolysed with an acid than a base
Polyesters are more easily hydrolysed with a base than an acid

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18
Q

Characteristics of addition polymerisation

A

Monomer contains a C=C bond
Backbone of polymer is a continuous chain of carbon atoms

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19
Q

Characteristics of condensation polymerisation

A

Two monomers each with two functional groups
One monomer with two different functional groups
Polymer contains ester or amide linkages

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20
Q

Haloalkane to nitrile

A

NaCN or KCN Ethanol Reflux

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21
Q

Haloalkane to amine

A

Excess ethanolic NH3 (or amines)
Heat

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22
Q

Nitrile to amine

A

LiAlH4 then dilute acid
Or Na and ethanol, reflux
Or H2, Ni/Pt catalyst, high temp and pressure

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23
Q

Nitrile to Carboxylic acid

A

Dilute HCI Reflux

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24
Q

Hydroxynitrile to carboxylic acid

A

Dilute HCI Reflux

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25
Q

Ketone to 2° alcohol

A

NaBH4 then water

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26
Q

Aldehyde to hydroxynitrile

A

HCN or NaCN

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27
Q

Ketone to hydroxynitrile

A

NaCN or HCN

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28
Q

Hydroxynitrile to amine

A

LiAlH4 then dilute acid
Or Na and ethanol, reflux
Or H2, Na/Pt catalyst, high temp and pressure

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29
Q

Aldehyde to 1° alcohol

A

NaBH4 then water

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30
Q

Alcohol to carboxylic acid

A

K2Cr2O7 H2SO4 Reflux

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31
Q

Alcohol to ester

A

Carboxylic acid, H2SO4 catalyst, heat
Or acyl chloride
Or acid anhydride

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32
Q

Carboxylic acid to ester

A

Alcohol, H+ (acid) catalyst

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33
Q

Ester to carboxylic acid

A

Dilute acid or alkali

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34
Q

Ester to carboxylate

A

OH-
Heat

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35
Q

Acyl chloride to ester

A

Alcohol
20°C

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36
Q

Acyl chloride to carboxylic acid

A

Cold H2O

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37
Q

Carboxylic acid to acyl chloride

A

SOCI2

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38
Q

Acyl chloride to 1° amide

A

NH3 20°

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39
Q

Acyl chloride to 2° amide

A

Primary amine 20°

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40
Q

Benzene to nitrobenzene

A

Conc HNO3
Conc H2SO4
Warm

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41
Q

Benzene to halobenzene

A

X2
AlCl3 catalyst
Warm

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42
Q

Benzene to alkyl benzene

A

Haloalkane
AlCl3 catalyst
Reflux

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43
Q

Benzene to phenylketone

A

Acyl chloride
AlCl3 catalyst
Reflux

44
Q

Nitrobenzene to phenylamine

A

Tin
Conc HCl
Reflux then add NaOH

45
Q

Phenol to sodium phenoxide

A

NaOH
20°

46
Q

Phenol to phenyl ester

A

Acyl chloride
20°

47
Q

Phenol to 2-nitrophenol or 4 nitrophenol

A

Dilute HNO3
20°

48
Q

Phenol to 2,4,6 tribromophenol

A

Bromine water (Br2)
20°

49
Q

How do you get an amine from ammonia

A

If one or more hydrogen is replaced by an organic group

50
Q

What determines if an amine is primary, secondary, tertiary or quaternary

A

This is determined by how many alkyl groups the nitrogen atom is bonded to

51
Q

What do you get if the nitrogen atom is bonded to 4 alkyl groups

A

You get a positively charged quaternary ammonium ion

52
Q

Difference between an aliphatic and aromatic amine

A

Aliphatic: when the amine doesn’t contain any benzene structures
Aromatic: amine contains a benzene ring

53
Q

Are amines basic or acidic

A

Amines are bases
There’s a lone pair of electrons on the nitrogen atom of an amine that’s able to accept protons (H+ ions)

54
Q

How do amines react with acids

A

Amines are neutralised by acids to make ammonium salts.
E.g. ethylamine reacts with HCl to form ethylammonium chloride

55
Q

How to get an amine from haloalkane

A

Heat the haloalkane with an excess of ethanolic ammonia

56
Q

Possible products of preparing an amine from a haloalkane

A

Get a mixture of primary, secondary and tertiary amines, and quaternary ammonium salts
More than one hydrogen is likely to be substituted.
Can separate the products using fractional distillation.

57
Q

How can multiple different products be formed in stages from bromoethane reacting with ammonia

A

Reacts to form ethylamine
This is nucleophilic substitution
Ethylamine can then react with ammonia and bromoethane again to form diethylamine
Can continue until quaternary amine formed

58
Q

How can multiple different products be formed in stages from bromoethane reacting with ammonia

A

Reacts to form ethylamine
This is nucleophilic substitution
Ethylamine can then react with ammonia and bromoethane again to form diethylamine
Can continue until quaternary amine formed

59
Q

How to form an aromatic amine

A

Must reduce a nitro compound
Nitro compounds must be reduced using 2 steps
Heat mixture of nitro compound, tin and conc HCl under reflux to make a salt
Then add NaOH to get aromatic amine

60
Q

What are amides

A

Derivatives of carboxylic acids
Contain functional group -CONH2

61
Q

Why do amides behave differently from amines

A

The carbonyl group pulls electrons away from the rest of the -CONH2 group

62
Q

What types of amides can you get

A

Can be either primary, secondary or tertiary amides
This depends on how many carbon atoms the nitrogen is bonded to

63
Q

What functional groups do amino acids have

A

Amino acids have a basic amino (NH2) group and acidic carboxylic group (COOH)

64
Q

Structure of an α (alpha) amino acid

A

This is where both groups are attached to the same carbon atom (the α (alpha) carbon)
The general formula of an alpha amino acid is RCH(NH2)COOH

65
Q

How do amino acids react with alkalis

A

The carboxylic acid group in the amino acid can react with an alkali to form a conjugate base: RCH(NH2)COO-
This can combine with a positive ion to form a salt:

66
Q

How do amino acids react with acid

A

The amino group can react with an acid to form a salt of the conjugate acid
E.g:

67
Q

How do amino acids react with alcohols

A

Carboxylic acid group in an amino acid can react with an alcohol to form an ester
Requires strong acid catalyst (normally H2SO4)

68
Q

What is a chiral carbon

A

A chiral (or asymmetric) carbon atom is one which has four different groups attached to it.

69
Q

What does a chiral carbon atom mean for the possible structures of the molecule

A

It’s possible to arrange the groups in two different ways around the carbon atom so that two different molecules are made
These molecules are called enantiomers or optical isomers

70
Q

What are enantiomers

A

Enantiomers are mirror images of eachother
No matter which way you turn them, they can’t be superimposed

71
Q

What does being optically active mean for a molecule

A

Optical isomers are optically active
They can rotate plane-polarised light
One enantiomer rotates it in a clockwise direction
The other rotates it the same amount but in an anticlockwise direction

72
Q

Difference between normal light and plane polarised light

A

Normal light vibrates in all directions
Plane-polarised light only vibrates in one direction

73
Q

How to identify the different enantiomers

A

Can be identified as D and L isomer
(don’t need to know which is which)

74
Q

How do you normally find chiral compounds in nature

A

Chiral compounds are common in nature
Usually only 1 enantiomer can be found
E.g. all naturally occurring amino acids are L-amino acids and most sugars are D-isomers

75
Q
A
76
Q
A
77
Q
A
78
Q

When is an amine most reactive

A

When it has the maximum amount of R groups attached to the Nitrogen
They donate electron density towards the lone pair to make it more effective to act as a nucleophile

79
Q

How to turn an ammonium salt back into an amine

A

React it with a base (NaOH) to reform the amine, a salt from the base (NaCl) and H2O

80
Q

Name

A
81
Q

What is a molecule that can be superimposed called

A

If a molecule can be superimposed on its mirror image, it’s achiral and it doesn’t have an optical isomer.

82
Q

How does recrystallisation work

A

Solid is dissolved in minimum amount of warm solvent to make a saturated solution
Let it cool and solubility of product falls
It then forms crystals when it reaches a point when it can’t stay in solution

83
Q

Process of recrystallisation

A

Very hot solvent is added to impure solid until it just dissolves
Produces saturated solution of impure product
Solution left to cool and crystals of product form
Impurities stay in solution as they are in small amounts so take longer to crystallise
Crystals then removed by reduced pressure filtration and washed in ice cold solvent
Then leave to dry to give crystals of pure product

84
Q

How do you make a carbon chain longer during organic synthesis

A

Need reactants and reagents that have a nucleophilic or electrophilic carbon atom
Cyanide (CN-) has a negatively charged carbon atom which acts as a nucleophile
It reacts with carbon centres that have a slight positive charge to create a new carbon bond
This produces a nitrile

85
Q

What specific reagents to use to increase the carbon chain

A

React a compound that contains a slightly positive carbon centre with a cyanide reagent:

KCN, NaCN, HCN

86
Q

Mechanism for the reaction between a haloalkane and cyanide ion

A

Nucleophilic substitution

87
Q

How to increase carbon chain using nucleophilic substitution

A

Relfux haloalkane with NaCN or KCN in ethanol to make it undergo nucleophilic substitution to form the nitrile

88
Q

How to increase carbon chain using nucleophilic addition

A

Aldehydes and ketones contain a polar C=O
Mixing them with hydrogen cyanide (HCN) will allow the CN- with react with the positive carbon centre to form a hydroxynitrile

89
Q

Mechanism for increase carbon chain length with nucleophilic addition

A
90
Q

Why are nitrile groups useful in 2 step synthesis

A

Nitrile (or hydroxynitrile) are very reactive meaning they can be made into a new functional group

91
Q

How to reduce a nitrile and hydroxynitrile to a primary amine

A

Can use LiAlH4 (strong reducing agent) then dilute acid
Na and ethanol
H2, Ni or Pt catalyst at high temperature and pressure (catalytic hydrogenation)

92
Q

Equations for reducing nitrile to a primary amine using LiAlH4 or H2

A
93
Q

Equation for reducing hydroxynitrile to a primary amine using LiAlH4

A
94
Q

Why is catalytic hydrogenation used to reduce nitriles more than other methods

A

LiAlH4 and sodium are too expensive for industrial use

95
Q

How to turn a nitrile or hydroxynitrile into a carboxylic acid

A

Refluxing with dilute HCl causes the nitrile group to be hydrolysed to form a carboxylic acid

96
Q

Equation for hydrolysing nitrile to carboxylic acid

A
97
Q

Equation for hydrolysing hydroxynitrile to carboxylic acid

A
98
Q
A
99
Q

Why is the solvent used in recrystallisation important

A

Recrystallisation will only work if the solid is very soluble in the hot solvent but nearly insoluble when the solvent is cold
If product isn’t soluble enough in the hot solvent then it won’t be able to be dissolved at all
If the product is too soluble in the cold solvent, most of it will stay in solution even after cooling
Means that when you filter, most of the product will be lost giving a low yield

100
Q

What is filtering under reduced pressure used for

A

Used to separate solid product from any liquid impurities
This is because the reduced pressure caused suction through the funnel causing the liquid to pass quickly into the flask which leaves behind dry crystals of the product

101
Q

How to carry out reduced pressure filtration

A

The reaction mixture is poured into a Büchner funnel with a piece of filter paper in it.
The Büchner funnel is on top of a sealed sidearm flask which is connected to a vacuum line, causing it to be under reduced pressure.

102
Q

How does melting and boiling points use to determine purity

A

Most pure substances have a specific melting and boiling point.
If they’re impure, the melting points lowered and the boiling point is raised.
If they’re very impure, melting and boiling will occur across a wide range of temperatures.

103
Q

How to accurately measure melting point

A

Put a small amount of the solid in a capillary tube and gently tap the tube to get the solid to fall to the bottom.
Place the tube in a beaker of oil with a very sensitive thermometer.
Slowly heat, with constant stirring until the solid just melts and read the temperature on the thermometer.

104
Q

How to check the purity of a product after melting point has been obtained

A

Can compare the experimental melting point to a known melting point of the substance to determine its purity
If the melting points are similar then your sample is quite pure
If the value is much lower than the standard value then your sample has impurities

105
Q

What amine is the most basic

A

Least: aromatic
Primary
Secondary
Most: tertiary

Tertiary have the most alkyl groups which donate electrons by inductive effect so there are more electrons present to readily donate and act as a nucleophile

A Level Chemistry (15 decks)

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