Question

How would I seperate benzophenone from benzoic acid in a under-grad lab? For the lab practical experiment, you will be given a 1.00-g sample of benzophenone contaminated with benzoic acid. Your task is to write your own protocol and complete as much of it as possible, with the objective being to obtain a pure sample of benzophenone in the highest percent recovery. Techniques to consider include the following:  Recrystallization  Extraction  Column chromatography  TLC/mp/bp  Distillation  Reflux  Drying of organic solvents  Evaporation  Vacuum and gravity filtration.

Answer 1

Benzophenone and Benzoic acid mixture can be seperated using extraction with a base (1M NaOH solution).

Protocol:

1. To the 1.00g sample add 10 - 15 ml of diethyl ether.( Both the compounds are readily soluble in ether)

2. To this ether solution add 10 -15 ml of 1M NaOH solution and mixed thoroughly.

(All Benzoic acid will be soluble in NaOH)

3. The mixture is allowed to stand for some time to allow the aqueous and organic layers to seperate.

4. Both layers are seperated.

5. The organic layer is thoroughly washed with dil.NaOH and then with water (to ensure no contamination is present).

6. It is taken into roundbottom fask and the solvent diethyl ether is evoparated on a waterbath.

7. The crude Benzophenone is recrystallised in CHCl₃ solvent.

8. The purity is tested by observing the melting point of Benzophenone(48-51⁰C)