Chemical methods - Purification of organic compounds
Besides these physical methods, few chemical methods have as well been utilized to separate a mixture of organic compounds. These techniques are based on the unique chemical properties of one class of organic compounds from the others one. For instance,
(a) Phenols should be separated from carboxylic acids on treatment along with an aqueous solution of NaHCO3. As carboxylic acids dissolve in NaHCO3 solution evolving CO2 but phenols generally do not react.
(b) Destructive distillation of wood provides pyroligneous acid which consist acetic acid (10%), acetone (0.5%) and methanol (3%). Acetic acid can be separated from this mixture through treating it with milk of lime while acetic acid forms the calcium salt. The reaction mixture on distillation provides a mixture of acetone and methanol (that can be further separated by fractional distillation into individual components as mentioned above) when the calcium salt remains as residue in the flask. The calcium salt is after that decomposed with dil HCl and distilled to afford acetic acid.
(c) A mixture of 1o, 2o and 3o amines might be separated by using either benzenesulphonyl chloride (Hinsberg's reagent) or diethyl oxalate (Hoffmann's method).