Esters

What are derivatives of carboxylic acids?

A compound that can be hydrolysed to form the parent carboxylic acid and all contain the acyl group - RCO

Name the 4 types of carboxylic acid derivatives

• Esters

• Acyl chloride

• Acid anhydride

• Amide

For esters, give:

• The general displayed formula

• The way of naming

1. Remove ‘oic acid’ and replace with ‘oate’

2. First word is alkyl chain attached to O on COO

For acyl chlorides, give:

• The general displayed formula

• The way of naming

1. Remove ‘oic acid’ from carboxylic acid and replace with ‘oyl chloride’

For acid anhydride, give:

• The general displayed formula

• The way they are formed

Removal of water from two carboxylic acids

Give 2 ways of making an ester - which produces a better yield?

• Carboxylic acid + alcohol → ester + water

• Acid anhydride (meaning no water) + alcohol → ester + carboxylic acid (produces a better yield)

Give the equation for esterificaion and the conditions needed

Alcohol + carboxylic acid → ester + water

• Conditions: heat, concentrated sulfuric acid catalyst

Give the 2 ways of making methyl ethanoate ( equations )

1. Methanol + ethanoic acid → methyl ethanoate

2. Methanol + ethanoic anhydride → methyl ethanoate + ethanoic acid

How is an acid anhydride formed?

By the removal of water from two carboxylic acid molecules

Define hydrolysis

The chemical breakdown of a compound into 2 compounds in the presence of water or aqueous solution of hydroxide ions

Give the 2 ways esters can be hydrolysed and their products

1. In hot aqueous acid to form carboxylic acids and alcohols

2. In hot aqueous alkali to form carboxylate salts and alcohols

Summarise acid hydrolysis

The reverse of esterification

Give the equation for acid hydrolysis of esters

Ester + water → alcohol + carboxylic acid

Describe the process of acid hydrolysis and conditions needed

1. The ester is heated under reflux with dilute sulfuric or hydrochloric acid, where water is present

2. The ester is broken down by the water, with the acid acting as a catalyst

3. Carboxylic acid and alcohol is formed

What can be said about the amount of reactants vs products in acid hydrolysis?

The reaction is at equilibrium

• There are always molecules of reactant and product present

  • Carboxylic acid will be present in the equilibrium mixture

Show the acid hydrolysis of propyl ethanoate

Show the acid hydrolysis of methyl 2-hydroxybenzoate

Summarise alkaline hydrolysis

• Alkaline hydrolysis is also known as saponifacation (process of making soaps)

• It is irreversible

Describe the process of alkaline hydrolysis and the conditions needed

1. The ester is heated under reflux with aqueous hydroxide ions ( sodium or potassium hydroxide)

2. This non-reversible reaction leads to the formation of a (sodium or potassium) carboxylate salt of the carboxylic acid and alcohol

Give the equation for alkaline hydrolysis

Ester + alkali _(aq) → carboxylate salt + alcohol

Show the alkaline hydrolysis of ethyl propanoate in sodium hydroxide

Give a brief method of making esters

1. Add alcohol and carboxylic acid into a boiling tube

2. Add concentrated sulfuric acid

3. Place the boiling tube in a hot water bath of 80 degrees

4. Leave for 5 minutes

5. Pour into a beaker of aqueous sodium carbonate to neutralise acids and remove the smell