Question

Provide a procedure to separate a mixture composed of 50% Ethyl Aminobenzoate, 40% Benzil, 10% and 1,4-dibromobenzene.

Answer 1

The mixture contains a base - ethyl aminobenzoate, a ketone - benzil and a neutral dihalide - p-dibromobenzene. First, the base is separated by dissolving the mixture in a suitable solvent like methylene chloride and adding a solution of hydrochloric acid to it and shaking the mixture vigorously. This results in the protonation of the base and gives ethyl aminobenzoate hydrochloride salt. This salt is soluble in water and so the organic layer only has the ketone and dihalide. Next, the aqueous layer is treated with a strong base like NaOH and DCM again to deprotonate the base and give pure ethyl benzoate in the DCM layer, which can be evaporated and recrystallized to afford pure ethyl aminobenzoate.

The organic layer now containing the ketone and dihalide is treated with sodium bisulphite solution. This salt forms a polar, water-soluble adduct with the ketone, leaving the ketone-bisulphite adduct in the aqueous layer and pure dibromobenzene will now be in the DCM layer, which can be evaporated to obtain pure dibromobenzene.

Finally, the aqueous layer containing the ketone-bisulphite adduct is treated with sodium bicarbonate or any such weak base along with DCM to give back benzil in the organic layer and leave bicarbonate bisulphite solution in the aqueous layer. This DCM layer is finally evaporated to result in the pure ketone - benzil.