Question

Why are ethanol and acetone unsuitable solvents for liquid-liquid extraction?

Answer 1

In the process of liquid-liquid extraction, a solute moves from one liquid phase to another liquid phase. The two liquid phases used must be immiscible or partially miscible with each other and form two separate layers. The basic principle is solute would move to that liquid phase in which it is more soluble. The principle of 'like dissolves like' works for solubility. The layer containing the solute/sample is separated and the solvent dried to obtain the sample.

Since most of the extractions are performed using aqueous solutions , the miscibility of the solvent with water is important. So, frequently, one of the solvents is water or an aqueous mixture . That means another liquid (other than water) can not be polar solvent. Now, acetone (CH₃ -CO-CH₃) and ethanol (C₂H₅OH) are polar solvents and they are completely miscible with most aqueous solutions. They would not form a separate layer with water. Solutes that are weakly polar or non-polar would not separate in such conditions.

Organic and non-polar solvents like ethyl acetate, methylene chloride, hexane etc. are therefore generally used solvents for this process.