Esters are a family of compounds which can be formed as a result of the reaction between a carboxylic acid and an and alcohol. Here you will find out how the reaction is performed and how to draw and name the product.
4.38. A fragrant functional group
When an alcohol reacts with a carboxylic acid an ester is formed. A water molecule is also produced in this process. Acid is used to catalyse the reaction.This is an example of a condensation reaction.
Esters of low molecular weight (Mr) are often used as fragrances and are found in essential oils.
Students should:
- 4.38C know the ester functional group
Carboxylic acids have a functional group which can be represented as -CO2H . If attached to an alkyl group (R) this becomes R-CO2H. The alcohol functional group is - OH. If attached to an alkyl group (R') this becomes R' - OH
When these two functional groups react together with the loss of a water molecule the result is an ester :
R groups.
The letter R is used for represent any alkyl group. An alkyl group is a length of alkane molecule ( minus one hydrogen atom) eg : - CH3 ( methyl) , - C3H7 (propyl).
4.39 - 4.40 Activity 1. Ethyl ethanoate would smell as sweet
Students should:
- 4.39C know that ethyl ethanoate is the ester produced when ethanol and ethanoic acid react in the presence of an acid catalyst
- 4.40C understand how to write the structural and displayed formulae of ethyl ethanoate
4.41 Activity 2. Ester by name, fruity by nature
Students should:
- 4.41C understand how to write the structural and displayed formulae of an ester, given the name or formula of the alcohol and carboxylic acid from which it is formed and vice versa
- 4.42C know that esters are volatile compounds with distinctive smells and are used as food flavourings and in perfumes
4.42 - 4.43 Activity 3. From Vomit to Pineapple
Students should:
- 4.43C practical: prepare a sample of an ester such as ethyl ethanoate
In this video you will see how a foul smelling carboxylic acid can be changed into the sweet smell of pineapple. The reaction involves a carboxylic acid combining with an alcohol to form an ester and shows two important laboratory preparation and separation techniques.