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Chemistry > Chapter 26 > Flashcards

Chapter 26 Flashcards

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1
Q

What is a carboxylic acid?

A

It is an organic base which contains a carboxyl functional group COOH/CO2H. The carboxyl group contains both a carbonyl group and a hydroxyl group.

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2
Q

How do you name carboxylic acids?

A

Add -oic acid to the stem of the longest carbon chain

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3
Q

What is two carboxylic acids called?

A

dioic acids

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4
Q

Are carboxylic acids polar?

A

They are due to the C=O and the O-H in which hydrogen bonds form between the O-H

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5
Q

How many carbon atoms are carboxylic acids soluble for?

A

4

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6
Q

What happens to solubility as a carbon number increases?

A

The solubility decreases as the non-polar parts have a greater effect on the overall polarity. The lower molecular weight ones are very soluble.

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7
Q

What happens when there is more than one acid group

A

The solubility increases as they form more hydrogen bonds with water.

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8
Q

Do carboxylic acid have high or low melting and boiling points?

A

They have relatively high boiling points

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9
Q

What are carboxylic acid classified as?

A

Weak acids

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10
Q

What happens when a carboxylic acid dissolve in water?

A

They partially dissociate releasing H+ ions into the aqueous solution. (PROTON DONORS)

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11
Q

What two types of reactions do carboxylic acids undergo?

A

Redox - with metals

Neutralisation - with bases (alkalis, metal oxides and carbonates)

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12
Q

Carboxylic acid + metal

A

salt + hydrogen

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13
Q

Carboxylic acid + base

A

salt + water

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14
Q

What salts do carboxylic acids form?

A

carboxylate salts

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15
Q

How are carboxylate salts named?

A

-oate

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16
Q

What’s the observation of a redox reaction with a carboxylic acid and metal?

A

Effervescence and the metal disappearing

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17
Q

What observations are there when you test for a carboxylic acid functional group?

A

The bubbles of gas evolved.

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18
Q

What are carboxylic acid derivatives?

A

Compounds which can be hydrolysed to form a parent carboxylic acid.

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19
Q

What do all carboxylic acid derivatives have?

A

An acyl group in their structure

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20
Q

How do you name an acyl chloride?

A

Remove the -oic acid

Replace with -oyl chloride

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21
Q

How can acyl chlorides be prepared?

A

These are prepared from their carboxylic acid by a reaction with thionylchloride SOCl2. Other products are SO2, HCl which evolve into gases leaving only acyl chloride. This should be carried out in a fume cupboard as the products are harmful.

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22
Q

How reactive are acyl chlorides?

A

They are very reactive and are easily converted into carboxylic acid derivatives, which have good yields so are useful in organic synthesis.

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23
Q

What are the carboxylic acid derivatives?

A

Ester, acyl chloride, acid anhydride, amide

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24
Q

What can acyl chloride react with?

A

Nucleophiles by losing the chloride ion whilst retaining the C=O bond

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25
Q

What are nucleophiles?

A

Electron pair donors

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26
Q

What is a condensation reaction?

A

A reaction in which two molecules react together to form a larger molecule with the elimination of a small molecule (addition followed by elimination)

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27
Q

What conditions are needed for the reaction of acyl chlorides with alcohols to form esters?

A

Anhydrous conditions

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28
Q

Why doesn’t carboxylic acids form esters from phenols and what is used instead?

A

Carboxylic acids are not reactive enough to form esters and phenols. Acyl chlorides and acid anhydrides a more reactive than carboxylic acids which reacts with phenols to produce phenyl esters neither need an acid catalyst.

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29
Q

Why are unholy just condition is used when reacting acyl chlorides as well as when forming carboxylic acids?

A

Acyl chlorides are very reactive, which react violently with water to produce a carboxylic acid and hydrogen chloride gas (dense steamy fumes). When using acyl chlorides in a reaction it must be carried out under anhydrous conditions.

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30
Q

What do ammonia and amines act as?

A

Nucleophiles by donating a lone pair of electrons on the nitrogen to the electron deficient carbon.

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31
Q

What does ammonia and acyl chlorides form?

A

Primary amide

32
Q

What does a primary amide and acyl chloride form?

A

Secondary amide

33
Q

How do acid anhydrides react?

A

React in a similar way to acyl chlorides with alcohols, phenols, ammonia and amines. But they are less reactive so useful in lab work.

34
Q

How is an acid anhydride formed?

A

By the loss of water from two water molecules of a carboxylic acid.

A CONDENSATION REACTION OCCURS

35
Q

What does an acid anhydride and a phenol form?

A

An ester and carboxylic acid

36
Q

What are esters?

A

They are carboxylic acid derivatives with an acyl group , the OH group is replaced OR

37
Q

How do you name esters?

A

Remove -oic acid

Replace with -oate

38
Q

What is esterification?

A

It is the reaction of an alcohol with a carboxylic acid to form an ester. The alcohol is warmed with carboxylic acid and a small amount of concentrated H2SO4 which acts as a catalyst.

39
Q

How can you distinguish an ester?

A

As it has a distinct fruity/fragrant smell

40
Q

What is hydrolysis?

A

The chemical breakdown of a compound in the presence of water or aqueous solution

41
Q

Do esters react slow or fast with water?

A

Slow so they need a catalyst

42
Q

What is acid hydrolysis?

A

It’s the reverse of esterification, the ester is heated under reflux with dilute aq acid. The ester is broken down by water, the acid acts as a catalyst which forms a carboxylic acid and an alcohol.

43
Q

What is alkaline hydrolysis?

A

It’s saponification which is reversible. The ester is heated under reflux with aqueous OH- to form a carboxylate ion and an alcohol.

44
Q

What is used to detect the carbonyl group (ketone/aldehyde)?

A

Brady’s reagent, 2,4 dinitrophenylhydrazine (2,4,DNP)

45
Q

What is the positive test of using Brady’s reagent?

A

A yellow/orange precipitate when a ketone or aldehyde is present

46
Q

What is the Brady solution?

A

2,4 DNP dissolved in methanol and sulphuric acid

47
Q

Describe the experiment of distinguishing the carbonyl group?

A
  1. Add 5 cm depth of a solution 2, 4DNP to clean test tube.
  2. Add three drops of an unknown compounds and leave to stand.
  3. If no crystals form add a few drops of sulphuric acid. 4. A yellow/orange precipitate indicates that an aldehyde or ketone is present.
48
Q

How are aldehydes and ketones identity determined?

A

They are determined by finding the melting point of the precipitate formed. The precipitate is separated by filtration then recrystallise before the melting point is taken. The melting point is compared with known values.

49
Q

How do you distinguish between aldehydes and ketones?

A

Tollen’s reagents is used which is a solution of silver nitrate in aqueous ammonia.

50
Q

What happens if an aldehyde is present?

A

A silver mirror forms

51
Q

What is the chemistry behind the silver mirror formation?

A

Tolins reagent contain silver ions which act as an oxidising agent in the presence of ammonia. The silver ions are reduced to silver and the aldehyde is oxidised to a carboxylic acid.

52
Q

Will a silver mirror form when added to ketones?

A

No because they can’t oxidise further.

53
Q

Describe the experiment when distinguishing between an aldehyde and a ketone?

A
  1. In a clean test tube add 3 cm depth of silver nitrate. 2. Add sodium hydroxide to silver nitrate until a brown precipitate of silver oxide is formed.
  2. Add dilute ammonia until the brown precipitate dissolves to form a clear colourless solution this is known as Tollens reagent.

To identify the aldehyde:

  1. Add 2 cm depth of unknown solution into a clean test tube.
  2. Add an equal volume of freshly prepared tollens reagent.
  3. Leave the test tube to stand in a beaker of warm water, leave for 10-15 minutes and observe a silver mirror form.
54
Q

When a secondary alcohol is heated under reflux with acidified dichromate what is formed?

A

A ketone.

55
Q

When primary alcohol is heated under reflux with acidified dichromate what is formed?

A

carboxylic acid

56
Q

When primary alcohol is heated under distillation with acidified dichromate what is formed?

A

aldehyde

57
Q

What happens when a tertiary alcohol is heated under reflux?

A

No reaction occurs

58
Q

Where is the carbonyl functional group found in aldehydes?

A

At the end of the carbon chain.

59
Q

Where is the carbonyl functional group found in ketones?

A

Where it is joined to 2 different carbon atoms in the chain.

60
Q

What is the functional group of an aldehyde?

A

CHO

61
Q

What is the functional group of a ketone?

A

CO

62
Q

How do you name an aldehyde?

A

add -al

63
Q

How do you name a ketone?

A

add -one

64
Q

What do you ketones not undergo?

A

OXIDATION REACTIONS

65
Q

How can you also distinguish between an aldehyde and ketone?

A

How to hide oxidise into carboxylic acid when reflux with acidified dichromate which turns the orange dichromate solution green.

66
Q

What is this CO bond comprised of?

A

A pie bond and a Sigma bond. The Sigma bond is caused by a direct overlap of orbitals between the C and O. The pie bond is formed from an overlap of P orbitals above and below the plane of C and O atoms.

67
Q

Is the C = O polar?

A

It is polar due to the electronegativity difference between the carbon and the oxygen. The oxygen is more electronegative than carbon electron density in the double bond flies closer to the oxygen. Making carbon slightly positive and oxygen slightly negative. Due to the Delta plus on the carbon carbonyl compounds will react with nucleophiles.

NUCLEOPHILIC ADDITION

68
Q

What is a nucleophile?

A

An atom or group of atoms that is attracted to an electron deficient carbon atom where donates a pair of electrons to form a new covalent bond.

69
Q

What is NaBH4?

A

Sodium Tetrahyridoborate is used as a reducing agent to reduce aldehydes and ketones to alcohols. Aldehydes or ketones are usually warmed with NaBH4 an aqueous solution.

70
Q

What happens when aldehydes react with NaBH4?

A

It forms a primary alcohol

71
Q

What happens when ketones react with NaBH4?

A

It forms a secondary alcohol

72
Q

What does the [H] indicate?

A

Reducing agent

73
Q

Describe the nucleophilic addition with NaBH4?

A
  1. The lone pair of electrons from the hydride ion is attracted and donated to the Delta plus carbon atom on the C=O bond. A dative covalent bond is formed between the hydride ion and carbon.
  2. The C=O pi bond breaks in heterolytic fission forming a negatively charged intermediate.
  3. The oxygen atom donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate has been protonated to form an alcohol.
74
Q

What is HCN and what does it do?

A

It is hydrogen cyanide which adds across the C=O bond of aldehydes and ketones. When it is generated in situ sodium cyanide and sulphuric acid is used. It is extremely poisonous and boils just above room temperature.

75
Q

Describe the mechanism for nucleophilic addition of HCN?

A

The cyanide ion acts as a nucleophile so there will be a lone pair of electrons on the carbon.

  1. A lone pair on the carbon atom of the cyanide ion is a attracted and donated to the Delta plus carbon atom of the C=O bond, a dative bond forms.
  2. The pi C=O bond breaks by heterolytic fission forming a negatively charged intermediate.
  3. The intermediate is protonated due to the O donating a pair of electrons to a hydrogen ion to form a hydroxynitrile.
76
Q

Why is the nucleophilic addition with hydrogen cyanide a useful reaction?

A

As it provides a way to extend the carbon chain length.

Chemistry (23 decks)

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