Esters

What is the functional group of esters?

-COO

How are esters formed?

They are formed in the reaction between an alcohol and a carboxylic acid in the presence of an acid catalyst

Describe the reaction between ethanol and ethanoic acid in the presence of an acid catalyst

ethanol + ethanoic acid < -acid catalyst- > ethyl ethanoate

What is the structural formulae of ethyl ethanoate?

CH₃COOCH₂CH₃

What are the rules when writing formulae for an ester?

• Remove the -anol from the alcohol and replace it with -yl

• Remove the -oic acid from the carboxylic acid and replace it with -oate

What are the rules for drawing the structural formulae of esters

• H is lost from the alcohol

• OH is lost from the carboxylic acid

• H + OH forms H₂O

• Bond forms between C from carboxylic acid and O in alcohol

What are esters known and used for?

Esters are known be volatile compounds with distinctive smells

They are used as food flavourings and perfumes

Describe a practical preparing a sample of an ester such as ethyl ethanoate.

1. A mixture of ethanol, ethanoic acid and concentrated sulfuric acid is heated by a water bath or a electric heater

2. As esters are volatile, meaning they have low boiling points, they will evaporate first from the mixture

3. It is then distilled and collected in a separate beaker by condensation through a cooling jacket

4. The distillate can be smelt to check whether an ester has been produced

Why should we not use a Bunsen burner to heat the mixture?

The mixture contains ethanol, which is flammable

In the case that small quantities of ethanoic acid and sulfuric acid being collected in the process, what can be done to remove them?

To remove acid impurities, add sodium carbonate solution, until the mixture stops fizzing

In the case that ethanol is collected in the process, what can be done to remove it?

Add calcium chloride solution