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Biological Sciences Foundation Year > Carboxylic Acids and Derivatives > Flashcards

Carboxylic Acids and Derivatives Flashcards

1
Q

Describe the solubility of small carboxylic acids in water.

A

Small carboxylic acids (up to C4) dissolve in water in all proportions due to their ability to hydrogen bond with water molecules.

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2
Q

How does the solubility of carboxylic acids change with increasing carbon chain length?

A

The solubility of carboxylic acids rapidly reduces after C4, as larger acids are less able to hydrogen bond with water.

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3
Q

Define the acidity of carboxylic acids in water.

A

Carboxylic acids are weak acids in water, only slightly dissociating, but they can displace carbon dioxide from carbonates.

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4
Q

Explain the role of delocalisation in carboxylic acid salts.

A

Delocalisation stabilises carboxylic acid salts, making their dissociation more likely and resulting in equal C-O bond lengths.

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5
Q

How does increasing chain length affect the strength of carboxylic acids?

A

Increasing chain length pushes electron density onto the COO- ion, making it more negative and less stable, which decreases the acid’s strength.

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6
Q

What effect do alkyl groups have on carboxylic acid strength?

A

Alkyl groups are electron-releasing, which can decrease the stability of the COO- ion, making the acid less strong.

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7
Q

How do electronegative chlorine atoms influence carboxylic acid strength?

A

Electronegative chlorine atoms withdraw electron density from the COO- ion, making it less negative and more stable, which increases the acid’s strength.

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8
Q

Compare the acidity of propanoic acid and ethanoic acid.

A

Propanoic acid is less acidic than ethanoic acid due to the effects of chain length on stability.

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9
Q

Compare the acidity of chloroethanoic acid and ethanoic acid.

A

Chloroethanoic acid is more acidic than ethanoic acid because the chlorine atom withdraws electron density, increasing stability.

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10
Q

Define the naming convention for carboxylic acids.

A

Carboxylic acids are named with the ending ‘-oic acid’, and no number is necessary for the acid group as it is always at the end of the chain.

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11
Q

What is the naming convention for carboxylic acids with groups on both ends of the chain?

A

Carboxylic acids with groups on both ends of the chain are called ‘-dioic acids’.

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12
Q

Provide an example of a carboxylic acid and its name.

A

Propan-1-oic acid is an example of a carboxylic acid.

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13
Q

What is the significance of the ‘e’ in the name ethanedioic acid?

A

The ‘e’ in ethanedioic acid indicates the presence of carboxylic acid groups on both ends of the carbon chain.

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14
Q

Describe the process of esterification.

A

Esterification is the reaction between carboxylic acids and alcohols in the presence of a strong acid catalyst, resulting in the formation of esters and water.

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15
Q

Define the components of an ester name.

A

An ester name consists of two parts: the part ending in –yl comes from the alcohol, and the part ending in –anoate comes from the carboxylic acid.

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16
Q

How does the esterification reaction proceed?

A

The reaction proceeds as follows: carboxylic acid + alcohol ⇌ ester + water, and it is reversible.

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17
Q

What conditions are required for the esterification reaction?

A

The esterification reaction requires heating under reflux, often for several hours or days, and the presence of an acid catalyst, such as H2SO4.

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18
Q

Explain the yield of the esterification reaction.

A

The yield of the esterification reaction is typically low, around 50%.

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19
Q

What are the characteristics of esters used in perfumes?

A

Esters used in perfumes need to be non-toxic, soluble in solvents like ethanol, volatile, and not reactive with water.

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20
Q

List some uses of esters.

A

Esters are used in perfumes, flavorings, solvents for polar organic substances, and as plasticizers for polymers.

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21
Q

How do esters behave as solvents?

A

Esters can act as solvents for polar organic substances, but they do not form hydrogen bonds due to the absence of hydrogen bonded to a highly electronegative atom.

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22
Q

What is the boiling point of esters compared to their parent carboxylic acids?

A

Esters have a lower boiling point than the hydrogen-bonded carboxylic acids from which they are derived.

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23
Q

Describe the oxidation of methanoic acid.

A

Methanoic acid can be oxidized, unlike other carboxylic acids, due to its structure containing an aldehyde group, forming carbonic acid (H2CO3), which can decompose to give CO2.

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24
Q

What happens when carboxylic acids react with metals?

A

When carboxylic acids react with metals, they form salts and release hydrogen gas.

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25
Q

Explain the reaction of carboxylic acids with alkalis.

A

Carboxylic acids react with alkalis to form salts and water.

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26
Q

What is the result of carboxylic acids reacting with carbonates?

A

Carboxylic acids react with carbonates to form salts, water, and carbon dioxide.

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27
Q

How do plasticizers affect polymers?

A

Plasticizers increase the flexibility of polymers by allowing the polymer chains to move more easily over each other.

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28
Q

Describe the hydrolysis of esters with acid.

A

Esters can be hydrolysed by heating with dilute acid (HCl) under reflux, resulting in the formation of a carboxylic acid and an alcohol. This reaction is reversible and does not yield a good amount of products.

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29
Q

What are the products of ester hydrolysis with acid?

A

The products of ester hydrolysis with acid are a carboxylic acid and an alcohol.

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30
Q

Define the conditions required for ester hydrolysis with sodium hydroxide.

A

Ester hydrolysis with sodium hydroxide requires heating under reflux with dilute sodium hydroxide.

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31
Q

How does the hydrolysis of esters with sodium hydroxide differ from that with acid?

A

The hydrolysis of esters with sodium hydroxide goes to completion and is not reversible, while hydrolysis with acid is reversible and yields less product.

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32
Q

Explain the significance of using excess sodium hydroxide in ester hydrolysis.

A

Using excess sodium hydroxide ensures that the ester is completely hydrolysed, leading to a more complete reaction.

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33
Q

What happens to the carboxylic acid salt produced in sodium hydroxide hydrolysis?

A

The carboxylic acid salt produced is the anion of the carboxylic acid, which is resistant to attack by weak nucleophiles, making the reaction irreversible.

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34
Q

Describe the practical method for hydrolysing ethyl benzoate.

A

To hydrolyse ethyl benzoate, heat it with sodium hydroxide under reflux for 30 minutes, then cool the mixture and add hydrochloric acid to produce a precipitate of benzoic acid.

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35
Q

What is the result of adding hydrochloric acid to sodium benzoate after hydrolysis?

A

Adding hydrochloric acid to sodium benzoate produces benzoic acid and sodium chloride.

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36
Q

How can benzoic acid be purified after hydrolysis?

A

Benzoic acid can be purified using the steps outlined in practical guide AQA required practical 10 for the purification of an organic solid.

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37
Q

Explain why sodium benzoate is soluble in water while benzoic acid is not.

A

Sodium benzoate is ionic and soluble in water, whereas benzoic acid is not soluble due to its molecular structure.

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38
Q

Define fats and oils in terms of their chemical structure.

A

Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids).

39
Q

Describe the process of hydrolysis of fats and its products.

A

Hydrolysis of fats produces soap, glycerol, and long chain carboxylic (fatty) acids.

40
Q

Explain the role of long chain carboxylic acids in soap formation.

A

Long chain carboxylic (fatty) acids produced by the hydrolysis of fats act as soaps, with a polar hydrophilic end that mixes with water and a non-polar hydrophobic chain that mixes with grease.

41
Q

How does glycerol interact with water?

A

Glycerol forms hydrogen bonds easily and is readily soluble in water.

42
Q

List some common uses of glycerol.

A

Glycerol is used in cosmetics, food, and in glues.

43
Q

Describe the process of converting vegetable oils into biodiesel.

A

Vegetable oils can be converted into biodiesel by reacting with methanol in the presence of a strong alkali catalyst.

44
Q

What is biodiesel composed of?

A

Biodiesel is a mixture of methyl esters of long chain carboxylic acids.

45
Q

Discuss the carbon neutrality of biodiesel production.

A

Biodiesel produced from plants is considered carbon-neutral because the carbon dioxide released when burned was previously absorbed by the plants during photosynthesis.

46
Q

What factors can affect the carbon neutrality of biodiesel?

A

The carbon neutrality of biodiesel can be affected by the energy needed for irrigation, oil extraction, heating the reaction, and processing the fuel if fossil fuels are used.

47
Q

Identify a potential issue related to biodiesel production and food supply.

A

Biodiesel production can impact the availability of land for food production.

48
Q

Describe the main difference in by-products between acyl chlorides and acid anhydrides during reactions.

A

Acyl chlorides primarily produce HCl as a by-product, while acid anhydrides produce RCOOH.

49
Q

Define the reactivity of acyl chlorides compared to carboxylic acids.

A

Acyl chlorides are much more reactive than carboxylic acids due to the presence of good leaving groups.

50
Q

How do acyl chlorides react with water?

A

Acyl chlorides react with water to form carboxylic acids and HCl at room temperature.

51
Q

What is the observation when acyl chlorides react with water?

A

The reaction produces steamy white fumes of HCl.

52
Q

Explain the change in functional group when an acid anhydride reacts with water.

A

An acid anhydride reacts with water to form carboxylic acids.

53
Q

What is the result of the reaction between acyl chlorides and alcohol?

A

The reaction produces esters and HCl at room temperature.

54
Q

How do acid anhydrides react with alcohol?

A

Acid anhydrides react with alcohol to form esters and carboxylic acids at room temperature.

55
Q

Describe the advantage of using acyl chlorides over carboxylic acids for ester formation.

A

Using acyl chlorides for ester formation is advantageous because the reaction is quicker and not reversible.

56
Q

What is the general mechanism involved in the reactions of acyl chlorides and acid anhydrides?

A

The reactions involve a nucleophilic addition-elimination mechanism.

57
Q

How does the reactivity of acid anhydrides compare to that of acyl chlorides?

A

Acid anhydrides have similar reactivity to acyl chlorides but are generally less reactive.

58
Q

What are the conditions required for the reactions of acyl chlorides and acid anhydrides with water and alcohol?

A

The reactions occur at room temperature.

59
Q

Illustrate the reaction of ethanoyl chloride with water.

A

CH3COCl + H2O → CH3COOH + HCl (g)

60
Q

Describe the change in functional group when acyl chloride reacts with ammonia.

A

The acyl chloride changes to a primary amide.

61
Q

What reagent is used in the reaction of acyl chloride to form a primary amide?

A

Ammonia is the reagent used.

62
Q

Identify the conditions required for the reaction of acid anhydride with ammonia.

A

The reaction occurs at room temperature.

63
Q

How does the reaction of acyl chloride with primary amines differ from that with ammonia?

A

The reaction with primary amines produces a secondary amide instead of a primary amide.

64
Q

What is the observation when acyl chloride reacts with ammonia?

A

White smoke of NH4Cl is given off.

65
Q

Define the mechanism involved in the reactions of acyl chlorides and acid anhydrides with amines.

A

The mechanism involved is nucleophilic addition-elimination.

66
Q

Explain the product formed when CH3COCl reacts with 2NH3.

A

The product formed is CH3CONH2 (a primary amide) and NH4Cl.

67
Q

What is the product of the reaction between acid anhydride and primary amine?

A

The product is a secondary amide.

68
Q

How does the reaction of CH3COCl with 2CH3NH2 proceed?

A

It produces RCONHCH3 (a secondary amide), CH3NH3, and Cl-.

69
Q

What is the significance of room temperature in these reactions?

A

Room temperature is the condition under which these reactions typically occur.

70
Q

Describe the change in functional group when acid anhydride reacts with ammonia.

A

The acid anhydride changes to a primary amide.

71
Q

What is the role of ammonia in the reactions described?

A

Ammonia acts as a nucleophile that reacts with acyl chlorides and acid anhydrides.

72
Q

Identify the product formed when CH3COOCCOCH3 reacts with 2NH3.

A

The product formed is N-methylethanamide.

73
Q

What happens to the acyl chloride when it reacts with a primary amine?

A

It forms a secondary amide.

74
Q

Explain the significance of the white smoke observed during the reaction with ammonia.

A

The white smoke indicates the formation of solid NH4Cl.

75
Q

Describe the first step in the recrystallisation process.

A

Dissolve the impure compound in a minimum volume of hot solvent, which should dissolve both the compound and impurities when hot, while the compound itself does not dissolve well when cold.

76
Q

Explain the purpose of using a hot filter in the recrystallisation process.

A

Hot filtering quickly removes insoluble impurities and prevents crystals from reforming during the filtration process.

77
Q

How does cooling the filtered solution affect the crystallisation process?

A

Cooling the filtered solution allows crystals to reform while soluble impurities remain in solution, increasing the yield of crystals.

78
Q

What is the function of a Buchner flask in the recrystallisation process?

A

A Buchner flask, connected to a water pump, reduces pressure and speeds up the filtration process to separate out crystals.

79
Q

Why is it important to wash the crystals with distilled water?

A

Washing the crystals with distilled water removes any remaining soluble impurities.

80
Q

What is the final step in the recrystallisation process?

A

Dry the crystals between absorbent paper to remove any residual moisture.

81
Q

Identify some reasons for loss of yield during recrystallisation.

A

Loss of yield can occur due to crystals being lost during filtering or washing, some product remaining in solution after recrystallisation, and other side reactions occurring.

82
Q

Define the role of ethanoic anhydride in the synthesis of aspirin.

A

Ethanoic anhydride is used to convert the phenol group in 2-hydroxybenzoic acid into an ester, and it is preferred over acid chlorides for being cheaper, less corrosive, and safer to use.

83
Q

Describe the appearance of crystals formed through recrystallisation compared to impure crystals.

A

The crystals formed through recrystallisation may appear as larger, needle-like crystals that are lighter in color than the impure crystals.

84
Q

What is the significance of using a minimum volume of solvent in recrystallisation?

A

Using a minimum volume of solvent helps to obtain a saturated solution, which is essential for effective crystallisation upon cooling.

85
Q

Describe the relationship between sample purity and melting point.

A

A very pure sample will have a sharp melting point, matching the value quoted in data books.

86
Q

How can the degree of purity of a sample be tested?

A

The degree of purity can be tested by determining the melting point or melting range of the sample.

87
Q

What is required for the heating oil used in melting point determination?

A

The heating oil must have a boiling point higher than the sample’s melting point and low flammability.

88
Q

Explain the setup for measuring melting point using a capillary tube.

A

A small amount of the sample is placed in a capillary tube, which is strapped to a thermometer immersed in heating oil.

89
Q

What happens to the melting point if impurities are present in the sample?

A

If impurities are present, the melting point will be lowered and the sample will melt over a range of several degrees Celsius.

90
Q

How can errors occur when measuring melting point?

A

Errors may occur if the temperature on the thermometer does not match the temperature in the actual sample tube.

91
Q

What equipment can be used to measure melting point?

A

Melting point can be measured using an electronic melting point machine or a practical setup with a thermometer and capillary tube.

92
Q

Define the melting point in the context of purity testing.

A

The melting point is the temperature at which a solid becomes a liquid, and it is used to assess the purity of a sample.

93
Q

What is the procedure for heating the sample in a melting point determination?

A

The sample is heated slowly near the melting point to accurately determine when it begins to melt.

Biological Sciences Foundation Year (17 decks)

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