How do you isolate benzoic acid from a mixture of biphenyl and benzoic acid?

Both benzoic acid and biphenyl are organic solutes, and therefore will dissolve in organic solvents. (ie: diethyl ether)

Benzoic acid (an acid) will react with a strong base (ie: NaOH) to form sodium benzoate (which is a water soluble salt) and aqueous NaCl.

Therefore, if you have a mixture of biphenyl and benzoic acid, you can dissolve it in an organic solvent (say diethyl ether) and add NaOH, to convert benzoic acid into a water soluble salt. (water is NOT soluble in organic solvents). therefore your mixture in solution will separate into two layers. The upper organic layer will contain biphenyl dissolved in ether, and the lower aqueous layer will contain the water soluble salt of benzoic acid and water. (as well as aqueous NaCl).

Using a separatory funnel, or other separation equpiment, the two layers can be separated.


The benzoic acid can be extracted by adding HCl which will convert the salt back into benzoic acid, and the solution can be chilled (to cause precipitation of benzoic acid) and then filtered by suction filtration, etc..


The biphenyl can be extracted by distillation, as ether is quite volatile and will evaporate easily (B.pt = 34.6 degrees Celsius)



Source: Chemistry Major :)