Question

How could you separate a mixture of starch, naproxen, and acetaminophen? Describe the laboratory procedure you would use.

Answer 1

Starch is a carbohydrate and it has a large number of glucose units joined by glycosidic bonds. Starch is insoluble in water.

Before solving this you should know some basic points. Carboxylic acids are acidic enough to dissolve in both 10% NaHCO₃ and 10% NaOH. Compare to carboxylic acids phenols, ArOH, are weak acids and phenols will not soluble in 10% NaHCO₃ but it will soluble in 10%NaOH.

First mixture of starch, naproxen, and acetaminophen dissolved in any organic solvent (like ethyl acetate or dichloromethane). Next add 10%aqs NaHCO₃ solution, If shake it, naproxen has carboxylic acid group it will react with NaHCO₃ and forms sodium salt of naproxen , this will dissolve in water so separate water layer and neutralize with dilute HCl you will get pure naproxen compound.

Now mixture has two compounds starch and acetaminophen, Next treat with 10% NaOH, acetaminophen has phenol group so it will come as a sodium salt just separate it and neutralize then you will get pure acetaminophen compound.

In organic solvent only starch will reamin.