Question

The substances given are 50% benzoic acid, 40% benzoin, and 10%1,4-dibromobenzene. I need a seperation scheme, i know i have to use extraction and recrytallization to seperate each. I am just confused which substances to use, the solvents available are water, 1.0M NaOH, 6.0m NaOH, 1.0M HCl, 6.0M HCl, 1M NaHCO3, saturated aq sodium chloride, dichloromethane, diethyl ether, 95% ethanol, methanol, isopropyl alcohol, acetone, hexane, and toluene. thank you for any help!

Answer 1

Separation scheme for three compounds

1) add diethylether (or dichloromethane) solvent. All three dissolves.

2) add 1M NaHCO3 solution. Benzoic acid reacts and forms sodium benzoate which goes in aqueous layer. The other two benzoin and 1,4-dibromobenzene remained in diethylether layer.

3) separate the two phases

4) acidify aqueous layer with 6.0 M HCl solution. Benzoic acid reprecipitates. Vacuum filtration gives the solid benzoic acid.

5) The organic layer is now completely dried off to give solid mixture of benzoin and 1,4-dibromobenzene.

6) Add minimal amount of hexane (a non-polar solvent). More non-polar 1.4-dibromobenzene dissolves in hexane leaving behind benzoin.

7) separate the hexane layer and evaporate to get 1,4-dibromobenzene.

8) Benzoin is separated as solid at the end.