Racemisation:
When equal amounts of dextrorotatory and laevorotatory isomers are mixed then the resulting mixture becomes optically inactive because optical activities of each isomer cancel each other. Such a mixture is called a racemic mixture and this phenomenon is called racemization. Racemisation can be done by the following methods:
1. By simple heating:
It is also called thermal racemisation. The racemic mixture of tartaric acid, lactic acid etc. can be obtained by this method.
2. Auto racemisation:
Racemisation of some compounds takes place at room temperature. It is called auto racemisation. For example, auto racemisation of dimethyl succinate takes place at room temperature.
3. Chemical racemisation:
When a racemic mixture is obtained by mixing a chemical then it is called chemical racemisation. For example, 2-butyl phenyl ketone gives a racemic mixture on adding an acid. We can represent the thermal racemisation of lactic acid as follows: