O2: 26 Compounds containing the carbonyl group

Question 1

What are aldehydes readily oxidised to?

Answer 1

Carboxylic acids.

Question 2

What are the chemical tests to distinguish between aldehydes and ketones? How do you carry them out?

Answer 2

Tollens’ reagent:
- a colourless solution of silver nitrate dissolved in aqueous ammonia
1. Add to the sample in a test tube and heat.
- Ag+ ions in Tollens’ are reduced to Ag atoms
- silver mirror forms if aldehyde present

Fehling’s solution:
- a blue solution of copper(II) ions dissolved in NaOH
1. Add to the sample in a test tube and heat.
- copper(II) ions are reduced to copper(I) oxide (brick-red precipitate) if aldehyde present

Question 3

Name and outline the mechanism for the reduction of an aldehyde/ketone to an alcohol. What are the conditions?

Answer 3

Nucleophilic addition.
Aqueous NaBH4.

Question 4

Name and outline the mechanism for the reaction between carbonyl compounds and KCN. What are the conditions?

Answer 4

Nucleophilic addition.
Aqueous KCN, followed by a dilute acid.

Question 5

What is formed when aldehydes and unsymmetrical ketones react with KCN, followed by a dilute acid?

Answer 5

Mixtures of enantiomers.
Because there’s an equal chance of the nucleophile attacking from above or below the C=O bond.

Question 6

What are the hazards of using KCN?

Answer 6

KCN is:
- an irritant
- extremely dangerous if ingested or inhaled
- can react with moisture to produce HCN, a highly toxic gas

Must wear gloves, safety goggles, a lab coat and work in a fume cupboard.

Question 7

What is the reduction equation for an aldehyde to an alcohol?

Answer 7

RCHO + 2[H] -> RCH2OH

Question 8

What is the reduction equation for a ketone to an alcohol?

Answer 8

RCOR + 2[H] -> RCHROH

Question 9

What is the equation for the reaction of an aldehyde with HCN?

Answer 9

RCHO + HCN -> RCH(OH)CN

Question 10

What is the equation for the reaction of a ketone with HCN?

Answer 10

RCOR + HCN -> RCR(OH)CN

Question 11

What is the structure of a carboxylic acid?

Answer 11

RCOOH

Question 12

What is the structure of an ester?

Answer 12

RCOOR’

Question 13

What strength is a carboxylic acid?

Answer 13

Weak.

Question 14

What happens when a carboxylic acid reacts with carbonates?

Answer 14

COOH liberates CO2 from the carbonates.

Question 15

What do carboxylic acids and alcohols react to make? What conditions are used?

Answer 15

Esters are produced in the presence of an acid catalyst.

Question 16

What are the common uses of esters?

Answer 16

In solvents, plasticisers, perfumes, and food flavourings.

Question 17

What can esters be hydrolysed to? Which conditions form which products?

Answer 17

In acidic conditions, alcohols and carboxylic acids are formed.
In alkaline conditions, alcohols and salts of carboxylic acids are formed.

Question 18

What is the general structure of an acid anhydride?

Answer 18

RCOOCOR

Question 19

What is the general structure of an acyl chloride?

Answer 19

RCOCl

Question 20

What is the general structure of an amide?

Answer 20

RC(O)N(R)(R)

Question 21

Name and outline the reaction mechanism of water/ alcohols/ ammonia/ primary amines with acyl chlorides/ acid anhydrides.

Answer 21

Nucleophilic addition-elimination.

Question 22

What are the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of aspirin?

Answer 22

• cheaper
• less corrosive
• doesn’t react with water as readily
• safer, as the by-product is ethanoic acid, not hydrogen chloride

Question 23

What are vegetable oils and animal fats esters of?

Answer 23

Glycerol.

Question 24

What can vegetable oils and animals fats be hydrolysed to in alkaline conditions?

Answer 24

Soap and glycerol.

Question 25

What is biodiesel a mixture of?

Answer 25

Methyl esters of long-chain carboxylic acids.

Question 26

How is biodiesel produced?

Answer 26

By reacting vegetable oils with methanol in the presence of a catalyst.