Organic 9: Carboxylic Acids and Derivatives

Question 1

How do you name carboxylic acid compounds?

Answer 1

Suffix is -oic acid
Carboxylic acid is always the root of the name
E.g. benzene carboxylic acid

Question 2

Describe the solubility of carboxylic acids.

Answer 2

Short chains are completely soluble in water
Because they are able to form hydrogen bonds to water molecules
Long chains are insoluble because the non-polar region predominates

Question 3

Describe the melting points of carboxylic acids.

Answer 3

Much higher than alkanes of similar molecular mass
Because of much stronger intermolecular forces (hydrogen bonds between molecules)

Question 4

How can you identify the melting points of carboxylic acids?

Answer 4

Using a Thiele tube

Question 5

Describe the main physical characteristic of carboxylic acids.

Answer 5

They have very characteristic smells
E.g. ethanoic acid is vinegar, butanoic acid smells like rancid butter

Question 6

What are esters?

Answer 6

Derived from carboxylic acids
The OH group is replaced with a hydrocarbon group (alkyl or aryl)

Question 7

How do you name esters?

Answer 7

The first part of the name comes from the alcohol group: methyl, ethyl, propyl, etc
The second part of the name comes from the carboxylic acid: methanoate, ethanoate, propanoate, etc

Question 8

Describe the physical characteristics of short chain esters.

Answer 8

Fairy volatile
Have fruity, pleasant smells
Often used in flavourings and perfumes
Can be used as solvents and plasticisers
Generally insoluble in water

Question 9

Describe the physical characteristics of longer chain esters.

Answer 9

Fats and oils
Insoluble in water

Question 10

How are esters formed?

Answer 10

Carboxylic acid + alcohol –> ester + water
Catalysed by strong acid catalyst (e.g. sulfuric acid)
Reversible reaction
Equilibrium mixture of reactants and products

Question 11

Write an equation for the esterification reaction of ethanoic acid and ethanol.

Answer 11

CH3COOH + C2H5OH –> CH3COOC2H5 + H2O

Question 12

Describe acid hydrolysis of esters.

Answer 12

Ester is refluxed with water and a strong, dilute acid catalyst usually hydrochloric acid or sulfuric acid
Reversible reaction
Lots of water must be added to push equilibrium to the right
Ester + water –> carboxylic acid + alcohol

Question 13

Describe base hydrolysis of esters.

Answer 13

Ester + dilute alkali –> carboxylate ion + alcohol
(reflux)
Produces a negatively charged carboxylate ion which bonds with a positively charged ion from the base used, forming a salt

Question 14

What is the mechanism for base hydrolysis?

Answer 14

Nucleophilic addition-elimination

Question 15

What are triglycerides?

Answer 15

Glycerol (propane 1,2,3 triol)
And 3 fatty acids

Question 16

How are triglycerides hydrolysed?

Answer 16

In acidic conditions to give a mixture of glycerol and fatty acids
By boiling with sodium hydroxide to produce glycerol and a mixture of sodium salts (soaps)

Question 17

Give a general equation for the hydrolysis of a triglyceride using sodium hydroxide.

Answer 17

Question 18

What is saponification?

Answer 18

The reaction of sodium hydroxide with triglyceride to produce glycerol and sodium salts

Question 19

Why is saponification useful?

Answer 19

Produces sodium salts
Useful as cleaning agents because they are ionic and dissociate to form Na+ and RCOO-
RCOO- has two ends: a non-polar hydrocarbon chain and a polar COO- group which is ionic
The hydrocarbon mixes with grease while the COO- mixes with water

Question 20

What is palmitic acid used for?

Answer 20

Making soaps

Question 21

What is oleic acid?

Answer 21

A monounsaturated fatty acid
Found in most fats and olive oil

Question 22

What is linoleic acid?

Answer 22

A polyunsaturated fatty acid
Present in many vegetable oils

Question 23

Describe the structure and uses of glycerol.

Answer 23

Readily forms hydrogen bonds due to its 3 OH groups
Very soluble in water
Used in pharmacy and cosmetics as it attracts water
Can be used to prevent ointments from drying out
Solvent in many medicines and toothpaste
Food colouring
Plasticiser

Question 24

What is biodiesel?

Answer 24

A type of fuel made from renewable organic matter
Better for the environment as it produces less pollutants when combusted

Question 25

How is rapeseed used as a biofuel?

Answer 25

Rapeseed oil is a triglyceride ester Reacted with methanol to form a mixture of methyl esters which can be used as fuel in diesel vehicles

Question 26

What makes carbonyl compounds so reactive?

Answer 26

The polar C=O bond is open to attack from nucleophiles As oxygen is more electronegative than carbon so attracts electrons, making oxygen delta positive and carbon delta negative The carbon is therefore available to be attacked by nucleophiles Whereas the oxygen can be attacked by positively charged species like protons

Question 27

Explain how a carboxylate ion forms.

Answer 27

If the hydrogen on the OH group of a carboxylic acid is lost The negative charge is shared over the whole carboxylate group (delocalisation) which makes the resulting ion more stable

Question 28

How do you test for carboxylic acids?

Answer 28

Sodium hydrogencarbonate reacts with carboxylic acids to release carbon dioxide Helps to distinguish them from other -OH compounds like alcohols

Question 29

How do carboxylic acids react with sodium hydroxide?

Answer 29

To form ionic salts and water e.g.

Question 30

How do carboxylic acids react with sodium hydrogen carbonate?

Answer 30

To form ionic salts, carbon dioxide, and water E.g.

Question 31

What is acylation?

Answer 31

The process by which an acyl group is added to another molecule

Question 32

What are acid derivatives?

Answer 32

Molecules that have the acyl group as part of their structure E.g. acyl chlorides and acid anhydrides

Question 33

Give a general equation for the formation of an acid derivative using a nucleophile.

Answer 33

Question 34

What are the three factors that determine how readily an acylation reaction will occur?

Answer 34

1) Magnitude of positive charge on the carbon (depends on what the variable group is) 2) How easily is the variable group lost 3) How strong the nucleophile is

Question 35

Why are acyl chlorides and acid anhydrides good acylating agents?

Answer 35

Because the Z groups withdraw electrons easily from the carbonyl carbon to make them more attractive to nucleophiles

Question 36

Which acid derivative is more reactive?

Answer 36

Acyl chlorides Chloride ions are stronger leaving groups as they leave behind a more stable ion

Question 37

Give the main nucleophiles that acid derivatives can react with in the order of their reactivity.

Answer 37

Primary amines Ammonia Alcohols Water

Question 38

What reaction occurs between acid derivatives and nucleophiles and what is the general mechanism?

Answer 38

Nucleophilic addition-elimination

Question 39

Why is ethanoic anhydride more useful in industry than ethanoyl chloride?

Answer 39

Cheaper Less corrosive Doesn't react readily with water Safer as the byproduct is ethanoic acid whereas ethanoyl chloride produces HCl Important in production of aspirin

Question 40

What is the systematic name for aspirin?

Answer 40

2-ethanoyloxybenzenecarboxylic acid

Question 41

What does aspirin do?

Answer 41

Treats moderate pain and fever Reduces risk of heart attacks and some cancers Risks: Intestinal bleeding