Question

How would you recrystallize a mixture of Benzoic acid and 2-Naphthol? Discuss the choice of solvent and recrystallization process. (Hint. Look up the solubility of these two compounds in different solvents)

Answer 1

First dissolve the mixture in diethyl ether solvent
Then, extract the benzoic acid into an aqueous layer by adding saturated NaHCO3 to the ether solution in a separating funnel. This should be done about 3-4 times with small amounts of the saturated NaHCO3 solution.

The benzoic acid will react with the NaHCO3 to form a salt that is soluble in the aqueous phase. The aqueous phase will be on the bottom because water is more dense than diethyl ether. 2-naphthol will not dissolve in saturated NaHCO3 because 2-napthol is not acidic and hence do not react with NaHCO3

Reaction may be represented as

C6H5COOH(aq) + NaHCO3(aq) --> C6H5COONa(aq) + CO2(g) + H2O

Now, separate the aqueous and ether layer and recover the 2-naphthol by evaporating the ether then dried

Recover the benzoic acid by adding small amounts of conc. HCl to the aqueous solution. The volume of acid you add depends on the amount of benzoic acid you have in the aqueous phase.

Reaction may be represented as

C6H5COONa(aq) + HCl(aq) --> C6H5COOH(s) + NaCi(aq)