Question

Outline briefly how you would separate a mixture of a basic and a neutral compound.

Hint: RNH2 + H3O+ --> RN+H3 + H2O

Answer 1

Let us assume base as Aniline and neutral compound as Naphthalene.

First add HCl(aq) to convert aniline to its salt, which dissolves in water. The neutral compound Naphthalene doesn't react and remains un-dissolved.

C6H₅NH₂ + HCl(aq) -------------> C₆H₅NH₃⁺ Cl^-

Next add diethyl ether which is immiscible with water. Naphthalene would be dissolved in ether and separates as a top organic layer above the lower water layer.

Then, Separate the top and bottom layer and evaporate the ether and recover the solid Naphthalene.

Add NaOH(aq) and more diethyl ether to the separated lower layer. NaOH converts the conjugate acid of aniline back to the free base Aniline, which now dissolves in ether as top layer. The NaCl produced remains with the water.

C₆H₅NH₃⁺Cl^- + NaOH    -----------> C₆H₅NH₂ + NaCl(aq) + H₂O

Separate the ether top layer and evaporate the ether to get aniline oil.

In this way, mixture of a basic and a neutral compound can be separated.