Introduction to Esters
Esters are used in the production of some sweets due to some having the smell of peardrops.
Structure of Esters
As described, esters are formed in the reaction between a primary alkanol and an alkanoic acid. In the reaction, the alkanoic acid loses its OH group and the alkanol the H on its OH group. These atoms combine to form the water that is lost. The free bonds then join to each other to form a single covalent bond. The compound formed is the ester.
For example, shown below is propanoic acid losing its OH group, ethanol losing an H atom from its OH group and the remaining molecules combining to form an ester.H H O H H O | | // | | || H - C - C - C → H - C - C - C - | | \ | | H H OH H H H H H H | | | | OH - C - C - H → - O - C - C - H | | | | H H H H H H O H H | | || | | H - C - C - C - O - C - C - H | | | | H H H H
The most reliable way to draw an ester is to follow all these steps.
- The ester should be divided into two carbon chains. Each carbon chain should begin with an end carbon atom and finish with the carbon next to the oxygen atom that is bonded to two carbon atoms.
- The carbon chain that ends with the carbon attached to both of the ester's oxygen atoms contains the same number of carbon atoms as the original alkanoic acid.
- The other carbon chain contains the same number of carbon atoms as the alkanol.
- As described in the relevant sections, the alkanol and alkanoic acid used to form the ester should then be named.
- The alkanol's name should have its -anol or -an-1-ol ending removed.
- To what remains, yl should be added. This is the first part of the ester's name.
- The alkanoic acid's name should then have its -anoic acid ending removed.
- To what remains, anoate should be added. This is the last part of the ester's name.
Therefore, if an ester was formed from butan-1-ol and propanoic acid:
- The first part of the ester's name (butyl) should come from the alkanol.
- The second part of the ester's name (propanoate) should come from the alkanoic acid.
- Therefore, the ester's name would be butylpropanoate.
Reactions of Esters
The main reaction that esters have is the reverse of how they are produced. When an ester reacts with water, an alkanol and an alkanoic acid are produced. Incidentally, this type of reaction is known as a hydrolysis reaction: one in which water is added to one molecule to form two molecules.