Question

Aniline is a base similar to ammonia.Suggest a scheme for seperating fluorenone from aniline. Show a schematic to support your answer.

Answer 1

Generally, ionic salts are soluble in water while their non-ionicacids (or bases) are insoluble in water. This can be used toyour advantage if you intend to separate a compound that is eitheracidic or basic through the use of extraction.

Aniline is indeed a base similar to ammonia. If you add anacid, it will become protonated, meaning it gains a proton and thusa positive charge. This makes it ionic and generallyinsoluble (or less soluble) in an organic solvent. If youstart with aniline and fluorenone in an organic solvent, addingaqueous acid will cause the aniline to protonate and migrate to theaqueous phase. As with any extraction, you must useimmiscible solvents (solvents that don't dissolve each other butform distinct phases or layers). In this case,dichloromethane, chloroform or toluene would work.

Regardless, the fluorenone, not having an acid/base character willremain in the organic phase. You can now physically separatethem by decanting or drawing off the aqueous layer (and thus theaniline). Now that you have the aqueous layer separate, youcan add base to it to neutralize the acid. This willprecipitate the aniline by changing it back to its basic, non-ionicform, which is insoluble in water.

Here's a simple diagram of what I have just described. Extraction of Aniline.