Liquid Liquid Extraction
Separation Of a Sample Mixture By Liquid-Liquid Extraction
Reading assignment: Techniques in Organic Chemistry 2nd ed pages 75-99. 3rd ed pages 113-140.
Topics and Techniques i) identification of solvent layers of two immiscible solvents ii) partioning of a compound between two immiscible solvents and determination of KD iii) liquid-liquid extraction with aqueous acids and bases with organic solvents. iv) use of drying agents Introduction Liquid-liquid extraction is a method used for the separation of a mixture using two immiscible solvents. The ability to separate compounds in a mixture using the technique of liquid-liquid extraction depends upon how differently the compounds of the sample mixture partition themselves between the two immiscible solvents. The technique of liquid-liquid extraction often involves a number of processes. First, the component mixture is dissolved in a suitable solvent and a second solvent that is immiscible with the first solvent is added (e.g., two solvents that are immiscible are diethyl ether and water). Next, the contents are thoroughly mixed (shaking) and the two immiscible solvents allowed separating into layers. The less dense solvent will be the upper layer, while the more dense solvent will be the lower layer. The components of the initial mixture will be distributed amongst the two immiscible solvents as determined by their partition coefficient. The relative solubility that a compound has in two given solvents can provide an estimation of the extent to which a compound will be partitioned between them. A compound that is more soluble in the less dense solvent will preferentially reside in the upper layer. Conversely, a compound more soluble in the more dense solvent will preferentially reside in the lower layer. Lastly, the two immiscible layers are separated, transferred and the component in that solvent is isolated by solvent evaporation and/or crystallization. The technique of liquid-liquid