# How does solvent extraction work?

Aug 17, 2014

Solvent extraction is a method for separating compounds based on their relative solubilities in two immiscible liquids.

#### Explanation:

The process is often used to separate an organic product from a reaction mixture.

Suppose your product is in an aqueous reaction mixture with other substances.

You might pour the mixture onto a separatory funnel and shake it with some ether.

The organic product dissolves preferentially in the ether. When the layers separate, you draw off the lower aqueous layer.

The ether layer contains most of your product, and you can remove the ether by distillation.

The process involves a dynamic equilibrium.

Product(aq) ⇌ Product(in ether)

The product distributes or partitions itself between the two solvents according to the equation

$K = {C}_{2} / {C}_{1}$, where

$K$ is the partition coefficient,
${C}_{2}$ is the concentration in ether, and
${C}_{1}$ is the concentration in water.

The value of $K$ is a measure of the different solubilities in the two solvents.

$K$ should have a large value, so that you can extract as much product as possible into the ether.