Dissolve the mixture in an apolar organic solvent, such as diethyl ether, and extract the acid with the addition of NaOH. The bezoic acid with ionize and go into the aqueous solution. Separate the two layers and add HCl to the aqueous layer to precipitate the benzoic acid. Wash the remaing ether solution with water and dry it with an anhydrous salt. Filter the ether solution and then remove the ether, the solvent, in order to obtain the pure benzoin.