Module 6: Chapter 26 - Carbonyls and Carboxylic Acids Flashcards
1
Q
What is formaldehyde?
A
Methanal
2
Q
What is acetone?
A
Propanone
3
Q
What is methanal/formaldehyde used for?
A
Preserving biological specimens
4
Q
What is acetone/propanone used for?
A
It is an industrial solvent and is also used in nail-varnish removers
5
Q
Can aldehydes be oxidised?
A
Yes
6
Q
Can ketones be oxidised?
A
No
7
Q
What is the equation for the oxidation of an aldehyde?
A
Aldehyde + [O] -> Carboxylic acid
8
Q
What are the conditions for the oxidation of an aldehyde?
A
- Reflux with potassium dichromate
- Sulfuric acid catalyst
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
10
Q
What is nucleophilic addition?
A
A chemical addition reaction in which a nucleophile forms a sigma bond with an electron-deficient species
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
12
Q
What is the reaction for reducing an aldehyde?
A
Aldehyde + 2[H] -> Alcohol
13
Q
How do you represent a reducing agent?
A
[H]
14
Q
What does reducing an aldehyde produce?
A
A primary alcohol
15
Q
What are the conditions for reducing an aldehyde?
A
NaBH₄ in an aqueous solution
16
Q
Whats the reaction for reducing a ketone?
A
Ketone + 2[H] -> alcohol
17
Q
What does reducing a ketone produce?
A
A secondary alcohol
18
Q
What are the conditions for reducing a ketone?
A
NaBH₄ in an aqueous solution
19
Q
What is NaBH₄?
A
Sodium Tetrahydrioborate (III)
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
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
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
23
Q
Why is the reaction of carbonyl compounds with HCN so useful?
A
It increases the length of the carbon chain
24
Q
What is the type of mechanism for the reduction of carbonyl compounds with NaBH₄?
A
Nucleophilic addition
25
What is the type of mechanism for the reaction of carbonyl compounds with Hydrogen Cyanide?
Nucleophilic addition
26
Draw the mechanism for the reduction of a carbonyl compound with NaBH₄
27
Describe the mechanism for the reduction of a carbonyl compound with NaBH₄
**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
28
What is the hydride ion?
:H⁻
29
What are the 2 steps addition to carbonyl groups usually consist of?
1. Nucleophilic attack on the carbonyl group to form a negatively charged intermediate
2. Protonation of the intermediate to form a hydroxy group
30
Draw the mechanism for the reaction of a carbonyl group with HCN
## Footnote
* 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
31
Describe the mechanism for the reaction of a carbonyl group with HCN
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
32
What can be used to detect carbonyl compounds?
A solution of 2,4-dinitrophenylhydrazine (**2,4-DNP**) will form a yellow/orange precipitate if a carbonyl functional group is present
33
What is brady's reagent?
A solution of 2,4-DNP dissolved in methanol and sulfuric acid
34
Describe how to test for carbonyl compounds
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
35
What colour is brady's reagent?
Pale orange
36
How can you distinguish between aldehydes and ketones?
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
37
What is tollens reagent?
A solution of silver nitrate in aqueous ammonia
38
How can you prepare a solution of tollens reagent?
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
What type of reaction is the reaction between an aldehyde and tollens reagent?
Redox reaction
40
What are the half equations in the redox reaction between an aldehyde and tollens reagent?
41
What is reduced in the redox reaction between an aldehyde and tollens reagent?
Silver ions are reduced to form a solid silver mirror
42
What is the carboxyl group?
A group containing both the hydroxyl and carbonyl functional group
43
What is the solubility of carboxylic acids in water?
Carboxylic acids with up to 4 carbon atoms are soluble in water
44
Explain the solubility of carboxylic acids in water
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
What type of acids are carboxylic acids?
Weak acids
46
What is the equation for the dissocation of methanoic acid?
47
What is the carboxylate ion?
48
What do carboxylic acids form in neutralisation reactions?
Carboxylate salts
49
What is the reaction between a carboxylic acid and a metal?
carboxylic acid + metal -> metal carboxylate + hydrogen
50
What is the reaction between a carboxylic acid and a metal oxide?
carboxylic acid + metal oxide -> metal carboxylate + water
51
What is the reaction between a carboxylic acid and an alkali?
carboxylic acid + alkali -> metal carboxylate + water
52
What is the reaction between a carboxylic acid and a carbonate?
carboxylic acid + metal carbonate -> metal carboxylate + water + carbon dioxide
53
What is the test to identify the carboxyl group?
Mix with a carbonate, if positive you should observe effervescence. No other organic compounds are acidic enough to sufficiently react with carbonates.
54
What is salicyclic acid?
2-hydroxybenzoic acid
55
What is a carboxylic acid derivative?
A compound that can be hydrolysed to form the parent carboxylic acid. All carboxylic acid derivatives contain the acyl group
56
What is the acyl group?
57
What are 4 carboxylic acid derivatives?
* Ester
* Acyl chloride
* Acid anhydride
* Amide
58
How is an acid anhydride formed?
It is formed from the removal of water from 2 carboxylic acid molecules
59
What is esterification?
The reaction of an alcohol with a carboxylic acid to form an ester
60
What is the reaction for esterification?
Carboxylic acid + Alcohol -> Ester + water
61
What are the conditions for esterificiation?
Warmed with a small amount of concentrated sulfuric acid
62
What is hydrolysis?
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
How can esters be hydrolysed?
* With an acid (acid hydrolysis)
* With an alkali (alkaline hydrolysis)
64
What is acid hydrolysis of an ester?
Acid hydrolysis of an ester is the reverse of esterification, it reforms the original carboxylic acid and the alcohol
65
How do you carry out acid hydrolysis of an ester?
* 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
What is the equation for acid hydrolysis of an ester?
Ester + water ⇌ Carboxylic acid + alcohol
| With a dilute aqueous acid catalyst!
67
What is saponification?
Alkaline hydrolysis of an ester
68
What is alkaline hydrolysis of an ester?
It is an irreversible reaction in which an ester forms a carboxylate ion and an alcohol
69
How do you carry out alkaline hydrolysis of an ester?
Heat an ester under reflux with aqueous hydroxide ions
70
What is the reaction for the alkaline hydrolysis of an ester?
Ester + aqueous hydroxide ions -> carboxylate ion + alcohol
71
What happens to the carboxylate ion formed in the alkaline hydrolysis of an ester
It will react with the metal ion from the alkali (which was used to provide the aqueous hydroxide ions)
72
How can you produce acyl chlorides?
React the parent carboxylic acid with thionyl chloride (SOCl₂)
73
What is the reaction of the production of acyl chlorides?
Carboxylic acid + thionyl chloride -> acyl chloride + sulfur dioxide (g) + hydrochloric acid (g)
74
Why must the reaction for the production of acyl chlorides be carried out in a fume cupboard?
SO₂ (g) and HCl (g) are harmful gaseous products
75
How do acyl chlorides react?
They react with nucleophiles by losing the chloride ion whilst retaining the C=O bond
76
What is the reaction of acyl chlorides with alcohols?
Acyl chloride + Alcohol -> Ester + Hydrogen chloride
77
What is the product of the reaction between acyl chlorides and alcohols?
Ester + HCl
78
What is the reaction of acyl chlorides with phenol?
acyl chloride + phenol -> Ester + Hydrogen Chloride
79
Why can acyl chlorides react with phenol to form esters but carboxylic acids cannot?
Acyl chlorides are far more reactive than carboxylic acids and therefore can react with phenols (whereas carboxylic acids can only react with alcohols)
80
What do acyl chlorides react with phenol to produce?
Ester (with a benzene ring) + HCl
81
What do acyl chlorides react with water to form?
Carboxylic acids + Hydrogen chloride
82
What is the reaction between acyl chlorides and water?
Acyl chloride + water -> carboxylic acid + HCl
83
Why do the reactions between acyl chlorides and alcohols/phenols not require a concentrated sulfuric acid catalyst?
Acyl chlorides are far more reactive than carboxylic acids
84
What is the reaction between an acyl chloride and ammonia?
Acyl chloride + ammonia -> **Primary amide** + Ammonium chloride
85
What are the products for the reaction between an acyl chloride and ammonia?
Primary amide + Ammonium chloride
86
What is the reaction between an acyl chloride and an a **primary amine**?
Acyl chloride + primary amine -> **secondary amide** + Methylammonium chloride
87
What are the products for the reaction between an acyl chloride and a primary amine?
Secondary amide + methylammonium chloride
88
How do acid anyhydrides react?
Acid anhydrides react in a **similar** way to acyl chlorides with:
* Alcohols
* Phenols
* Water
* Ammonia
* Primary amines
89
What is the reactivity of acid anhydrides compared to acyl chlorides?
Acyl chlorides are more reactive.
90
What is the reaction between an acid anhydride and phenol?
91
What is formed from the reaction with tollen's reagent an aldehyde?
Aldehyde + Tollens reagent -> Carboxylic acid + silver mirror
