Question

How are optical isomers separated?

Answer 1

Hint:Optical isomers also called enantiomers are a class of molecular isomers that differ only in terms of spatial arrangement around atoms with every other aspect of molecule like length of primary chain, substitution etc. being the same. Their physical and chemical properties in an achiral medium are also the same. They are differentiated by their property of bending light in a specific direction depending on its chirality.

Complete answer:
 To understand the method of separation of enantiomers, let us begin with a pair of enantiomers with absolute configuration of$R\& S$now let us add a homochiral species whose chirality is known to us as$R^\circ $, this species would interact with the enantiomers forming$RR^\circ ,SR^\circ $these newly formed species are diastereomeric in nature and thus have different physical and chemical properties and so can be separated out by methods like fractional distillation, crystallization etc.
Once separated these species could easily be treated with appropriate reaction conditions wherein the newly introduced part of$R^\circ $gets separated out and we are left with pure$R$and pure$S$enantiomers.
This whole process of separation of enantiomers is called Resolution of enantiomers.
These methods are exceedingly time consuming and protracted in nature. Nowadays some newly developed methods are in use wherein particular catalysts are developed that are specific to a particular antipode and react with that specific antipode with high selectivity to yield a product. This is known as kinetic resolution.

Note:Homochiral species like$\left( + \right) - tartrate$,$\left( - \right) - brucine$, $\left( + \right) - ephedrine$ etc. are commonly used in laboratories depending on the nature of enantiomeric pair which maybe carboxylic acid, Amine base, alcohol etc. So we must be highly cautious on our selection of the homochiral species to be used.