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A Level Chemistry > Module 6: Chapter 26 - Carbonyls and Carboxylic Acids > Flashcards

Module 6: Chapter 26 - Carbonyls and Carboxylic Acids Flashcards

1
Q

What is formaldehyde?

A

Methanal

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2
Q

What is acetone?

A

Propanone

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3
Q

What is methanal/formaldehyde used for?

A

Preserving biological specimens

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4
Q

What is acetone/propanone used for?

A

It is an industrial solvent and is also used in nail-varnish removers

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5
Q

Can aldehydes be oxidised?

A

Yes

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6
Q

Can ketones be oxidised?

A

No

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7
Q

What is the equation for the oxidation of an aldehyde?

A

Aldehyde + [O] -> Carboxylic acid

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8
Q

What are the conditions for the oxidation of an aldehyde?

A
  • Reflux with potassium dichromate
  • Sulfuric acid catalyst
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9
Q

Why do carbonyl groups and alkene groups react differently?

A

The C=C double bond in alkenes is non-polar, however the C=O double bond in carbonyl compounds is polar. Therefore it gives the carbon atom a δ+ dipole and the oxygen atom a δ- dipole. This allows it to react with some nucleophiles as the nucloephile is attracted to and attacks the δ+ carbon atom, resulting in addition across the C=O bond

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10
Q

What is nucleophilic addition?

A

A chemical addition reaction in which a nucleophile forms a sigma bond with an electron-deficient species

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11
Q

What is the reaction of carbonyl compounds with NaBH₄?

A

NaBH₄ is used as a reducing agent to reduce aldehydes and ketones to alcohols. The carbonyl compound is usually warmed with the NaBH₄ in an aqueous solution

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12
Q

What is the reaction for reducing an aldehyde?

A

Aldehyde + 2[H] -> Alcohol

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13
Q

How do you represent a reducing agent?

A

[H]

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14
Q

What does reducing an aldehyde produce?

A

A primary alcohol

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15
Q

What are the conditions for reducing an aldehyde?

A

NaBH₄ in an aqueous solution

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16
Q

Whats the reaction for reducing a ketone?

A

Ketone + 2[H] -> alcohol

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17
Q

What does reducing a ketone produce?

A

A secondary alcohol

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18
Q

What are the conditions for reducing a ketone?

A

NaBH₄ in an aqueous solution

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19
Q

What is NaBH₄?

A

Sodium Tetrahydrioborate (III)

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20
Q

What is the reaction of carbonyl compounds with HCN?

A

Hydrogen Cyanide, HCN, adds across the C=O bond of aldehydes and ketones to produce a hydroxynitrile

Carbonyl compound + HCN -> hydroxynitrile

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21
Q

What are the conditions for the reaction of a carbonyl compound with HCN?

A

Mixed with sodium cyanide and sulfuric acid

To provide the hydrogen cyanide as HCN is too dangerous to directly use

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22
Q

What are the risks of HCN?

A

Hydrogen cyanide is a colourless and an extremely poisonous liquid that boils slightly above room temperature

very dangerous chemical

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23
Q

Why is the reaction of carbonyl compounds with HCN so useful?

A

It increases the length of the carbon chain

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24
Q

What is the type of mechanism for the reduction of carbonyl compounds with NaBH₄?

A

Nucleophilic addition

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25
Q

What is the type of mechanism for the reaction of carbonyl compounds with Hydrogen Cyanide?

A

Nucleophilic addition

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26
Q

Draw the mechanism for the reduction of a carbonyl compound with NaBH₄

A
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27
Q

Describe the mechanism for the reduction of a carbonyl compound with NaBH₄

A

The NaBH₄ can be considered as containing the hydride ion (which acts as a nucleophile)
1. The lone pair of electrons from the hydride ion is attracted and donated to the δ+ carbon atom in the C=O bond
2. A dative covalent bond is formed between the hydride ion and the carbon atom of the C=O double bond
3. The π bond in the C=O double bond breaks by heterolytic fission, forming a negatively charged intermediate
4. The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate has then been protonated to form an alcohol

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28
Q

What is the hydride ion?

A

:H⁻

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29
Q

What are the 2 steps addition to carbonyl groups usually consist of?

A
  1. Nucleophilic attack on the carbonyl group to form a negatively charged intermediate
  2. Protonation of the intermediate to form a hydroxy group
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30
Q

Draw the mechanism for the reaction of a carbonyl group with HCN

A

  • The second stage can also be shown as protonation by water (as with the reaction with NaBH₄)
  • Make sure to draw the negative charge on the carbon atom in CN
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31
Q

Describe the mechanism for the reaction of a carbonyl group with HCN

A
  1. The lone pair of electrons from the cyanide ion is attracted and donated to the δ+ carbon atom in the C=O double bond. A dative covalent bond is formed
  2. The π-bond in the C=O double bond breaks by heterolytic fission, forming a negatively charged intermediate
  3. The intermediate is protonated by donating a lone pair of electrons to a hydrogen ion, to form the product
  4. A hydroxynitrile is formed
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32
Q

What can be used to detect carbonyl compounds?

A

A solution of 2,4-dinitrophenylhydrazine (2,4-DNP) will form a yellow/orange precipitate if a carbonyl functional group is present

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33
Q

What is brady’s reagent?

A

A solution of 2,4-DNP dissolved in methanol and sulfuric acid

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34
Q

Describe how to test for carbonyl compounds

A
  1. Mix a small amount of 2,4-DNP with methanol and sulfuric acid to produce brady’s reagent
  2. Add a few drops of the solution being tested
  3. A yellow/orange precipitate should form if there is a carbonyl group present
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35
Q

What colour is brady’s reagent?

A

Pale orange

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36
Q

How can you distinguish between aldehydes and ketones?

A

You can classify the sample as either an aldehyde or a ketone by heating it with tollen’s reagent in a water bath - if a silver mirror is formed it means the solution is an aldehyde

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37
Q

What is tollens reagent?

A

A solution of silver nitrate in aqueous ammonia

38
Q

How can you prepare a solution of tollens reagent?

A
  1. Add 3cm of aqueous silver nitrate to a test tube
  2. Add aqueous sodium hydroxide until a brown precipitate of silver oxide is formed
  3. Add dilute ammonia solution until the brown precipitatew just dissolves
39
Q

What type of reaction is the reaction between an aldehyde and tollens reagent?

A

Redox reaction

40
Q

What are the half equations in the redox reaction between an aldehyde and tollens reagent?

41
Q

What is reduced in the redox reaction between an aldehyde and tollens reagent?

A

Silver ions are reduced to form a solid silver mirror

42
Q

What is the carboxyl group?

A

A group containing both the hydroxyl and carbonyl functional group

43
Q

What is the solubility of carboxylic acids in water?

A

Carboxylic acids with up to 4 carbon atoms are soluble in water

44
Q

Explain the solubility of carboxylic acids in water

A

The C=O and O-H bonds in carboxylic acids are polar, allowing carboxylic acids to form hydrogen bonds with water molecules. However, as the number of carbon atoms increases the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule. Therefore only carboxylic acids with up to 4 carbon atoms are soluble in water

45
Q

What type of acids are carboxylic acids?

A

Weak acids

46
Q

What is the equation for the dissocation of methanoic acid?

47
Q

What is the carboxylate ion?

48
Q

What do carboxylic acids form in neutralisation reactions?

A

Carboxylate salts

49
Q

What is the reaction between a carboxylic acid and a metal?

A

carboxylic acid + metal -> metal carboxylate + hydrogen

50
Q

What is the reaction between a carboxylic acid and a metal oxide?

A

carboxylic acid + metal oxide -> metal carboxylate + water

51
Q

What is the reaction between a carboxylic acid and an alkali?

A

carboxylic acid + alkali -> metal carboxylate + water

52
Q

What is the reaction between a carboxylic acid and a carbonate?

A

carboxylic acid + metal carbonate -> metal carboxylate + water + carbon dioxide

53
Q

What is the test to identify the carboxyl group?

A

Mix with a carbonate, if positive you should observe effervescence. No other organic compounds are acidic enough to sufficiently react with carbonates.

54
Q

What is salicyclic acid?

A

2-hydroxybenzoic acid

55
Q

What is a carboxylic acid derivative?

A

A compound that can be hydrolysed to form the parent carboxylic acid. All carboxylic acid derivatives contain the acyl group

56
Q

What is the acyl group?

57
Q

What are 4 carboxylic acid derivatives?

A
  • Ester
  • Acyl chloride
  • Acid anhydride
  • Amide
58
Q

How is an acid anhydride formed?

A

It is formed from the removal of water from 2 carboxylic acid molecules

59
Q

What is esterification?

A

The reaction of an alcohol with a carboxylic acid to form an ester

60
Q

What is the reaction for esterification?

A

Carboxylic acid + Alcohol -> Ester + water

61
Q

What are the conditions for esterificiation?

A

Warmed with a small amount of concentrated sulfuric acid

62
Q

What is hydrolysis?

A

A reaction with water that breaks a chemical compound into two compounds, the H and OH in a water molecule become incorporated ito the 2 compounds

63
Q

How can esters be hydrolysed?

A
  • With an acid (acid hydrolysis)
  • With an alkali (alkaline hydrolysis)
64
Q

What is acid hydrolysis of an ester?

A

Acid hydrolysis of an ester is the reverse of esterification, it reforms the original carboxylic acid and the alcohol

65
Q

How do you carry out acid hydrolysis of an ester?

A
  • Heat the ester under reflux with a dilute aqueous acid
  • The ester will be broken down by the water, with the acid acting as a catalyst
66
Q

What is the equation for acid hydrolysis of an ester?

A

Ester + water ⇌ Carboxylic acid + alcohol

With a dilute aqueous acid catalyst!

67
Q

What is saponification?

A

Alkaline hydrolysis of an ester

68
Q

What is alkaline hydrolysis of an ester?

A

It is an irreversible reaction in which an ester forms a carboxylate ion and an alcohol

69
Q

How do you carry out alkaline hydrolysis of an ester?

A

Heat an ester under reflux with aqueous hydroxide ions

70
Q

What is the reaction for the alkaline hydrolysis of an ester?

A

Ester + aqueous hydroxide ions -> carboxylate ion + alcohol

71
Q

What happens to the carboxylate ion formed in the alkaline hydrolysis of an ester

A

It will react with the metal ion from the alkali (which was used to provide the aqueous hydroxide ions)

72
Q

How can you produce acyl chlorides?

A

React the parent carboxylic acid with thionyl chloride (SOCl₂)

73
Q

What is the reaction of the production of acyl chlorides?

A

Carboxylic acid + thionyl chloride -> acyl chloride + sulfur dioxide (g) + hydrochloric acid (g)

74
Q

Why must the reaction for the production of acyl chlorides be carried out in a fume cupboard?

A

SO₂ (g) and HCl (g) are harmful gaseous products

75
Q

How do acyl chlorides react?

A

They react with nucleophiles by losing the chloride ion whilst retaining the C=O bond

76
Q

What is the reaction of acyl chlorides with alcohols?

A

Acyl chloride + Alcohol -> Ester + Hydrogen chloride

77
Q

What is the product of the reaction between acyl chlorides and alcohols?

A

Ester + HCl

78
Q

What is the reaction of acyl chlorides with phenol?

A

acyl chloride + phenol -> Ester + Hydrogen Chloride

79
Q

Why can acyl chlorides react with phenol to form esters but carboxylic acids cannot?

A

Acyl chlorides are far more reactive than carboxylic acids and therefore can react with phenols (whereas carboxylic acids can only react with alcohols)

80
Q

What do acyl chlorides react with phenol to produce?

A

Ester (with a benzene ring) + HCl

81
Q

What do acyl chlorides react with water to form?

A

Carboxylic acids + Hydrogen chloride

82
Q

What is the reaction between acyl chlorides and water?

A

Acyl chloride + water -> carboxylic acid + HCl

83
Q

Why do the reactions between acyl chlorides and alcohols/phenols not require a concentrated sulfuric acid catalyst?

A

Acyl chlorides are far more reactive than carboxylic acids

84
Q

What is the reaction between an acyl chloride and ammonia?

A

Acyl chloride + ammonia -> Primary amide + Ammonium chloride

85
Q

What are the products for the reaction between an acyl chloride and ammonia?

A

Primary amide + Ammonium chloride

86
Q

What is the reaction between an acyl chloride and an a primary amine?

A

Acyl chloride + primary amine -> secondary amide + Methylammonium chloride

87
Q

What are the products for the reaction between an acyl chloride and a primary amine?

A

Secondary amide + methylammonium chloride

88
Q

How do acid anyhydrides react?

A

Acid anhydrides react in a similar way to acyl chlorides with:
* Alcohols
* Phenols
* Water
* Ammonia
* Primary amines

89
Q

What is the reactivity of acid anhydrides compared to acyl chlorides?

A

Acyl chlorides are more reactive.

90
Q

What is the reaction between an acid anhydride and phenol?

91
Q

What is formed from the reaction with tollen’s reagent an aldehyde?

A

Aldehyde + Tollens reagent -> Carboxylic acid + silver mirror

A Level Chemistry (31 decks)

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