SEPERATION OF ACIDIC AND NEUTRAL COMPOUNDS In this procedure, the unknown will contain an acid and a neutral compound. This unknown is dissolved in ether and extracted with a basic aqueous solution to remove the acidic unknown compound. This aqueous extract is then made acidic with dilute hydrochloric acid allowing for the isolation of the acidic compound. Finally, the neutral compound, which remains unextracted, is recovered by removal of the ether solvent.
SAFETY NOTE: Care should be taken to avoid ether spills on hands. If this occurs, wash your hands thoroughly with soap and water. Also, ether is highly flammable, and there should be no flames of any kind in the laboratory.
Obtain 1.0g of an unknown mixture, dissolve it in 50 ml of MTBE (methyl tertiary-butyl ether) or diethyl ether, and place it in a separatory funnel. To isolate the acid component of the mixture, extract this MTBE solution with 5% aqueous NaOH solution (3 x 15mL), and combine the extracts in a 125ml Erlenmeyer flask. Save the original MTBE solution in a labeled Erlenmeyer flask as it still contains your neutral compound. Then, back-extract the combined NaOH extracts with 15mL of fresh MTBE and dispose of this MTBE in the appropriate waste container. Place the aqueous solution containing your unknown acid in a Erlenmeyer flask and slowly add 10% HCl solution, swirling after each small portion is added. Collect any solid acid that precipitates by suction filtration, wash with cold water, and air dry. (If the acid separates as oil, it is recovered by an MTBE extraction – ask your instructor). To isolate the neutral unknown compound from the original MTBE solution, place the solution