Question

Identify which of the following solvents in each pair would constitute the upper layer in a liquid/liquid extraction solution. If layer separation would not be observed, indicate this by stating miscible. HINT knowing the physical properties of each solvent/solvent system are essential to answering this question correctly.

a) Ethyl acetate and 6M sodium hydroxide solution (aq):

b) Diethyl ether and water:

Answer 1

a) Ethyl acetate and 6M sodium hydroxide solution (aq)

Ethyl acetate would constitute the upper layer in a liquid/liquid extraction. Ethyl acetate is less polar than sodium hydroxide solution. For e.g. benzoic acid and benzyl both are soluble in ethyl acetate, If we take this mixture and add a base such as sodium hydroxide, benzoic acid will form its sodium salt and this ionic compound will have different solubility properties from the acid. it will be soluble in cold water, unlike both benzyl and neutral benzoic acid. This sodium salt can be removed as an aqueous solution, from which benzoic acid can be recovered simply by acidification.

b) Diethyl ether and water:

Diethyl ether would constitute the upper layer in a liquid/liquid extraction. Ether and water do not mix, if we mixed them they would quickly separate out. The density of diethyl ether is less than water, so its layer on top. This process frequently used to separate the products of organic synthesis.