Ibuprofen has a carboxylic acid functionality and has a pKa of 4.43. Aspirin has

Question

Ibuprofen has a carboxylic acid functionality and has a pKa of 4.43. Aspirin has a carboxylic acid functionality and has a pKa of 3.50. Acetaminophen has a phenol functionality and has a pKa of 9.51.

You will need the following information: The pKa of HCl is –7; pKa of carbonic acid is 6.52 and the pKa of water is 15.

1) You have a mixture of ibuprofen and aspirin that you wish to separate by extraction. The mixture is dissolved in methylene chloride.

a) Would reacting the mixture with an aqueous solution of NaOH separate one substance from the other? Why or why not?

2) You have a mixture of ibuprofen and acetaminophen that you wish to separate by extraction. The mixture is dissolved in methylene chloride.

a) Which among HCl, sodium bicarbonate and sodium hydroxide solutions would you use to separate the two substances?

b) Why can you not use the other two options from above to effect the separation (explain what would happen if you did).

Explanation / Answer

1) Reactiong the mixture with an aqueous solution of NaOH can't separate one substance from the other, because both aspirin and ibuprofen contains carboxylic acid functional groups, so both can react with NaOH to form salts of carboxylic acid. Hence both are soluble in aquesous solution this makes difficult separate the one substance from another.

2) a) Among the three HCl solution can be used to separate the acetaminophen from ibuprofen, because acetaminophen is a base hence it reacts with HCl and it comes into aqueous layer which leaves ibuprofen in organic layer. Ibuprofen is also having carboxylic acid group so it can't react with HCl, so it remains in organic layer.

b) Other two oprion are not suitable because they are bases, both ibuprofen and acetaminophen both have acidic groups such as carboxylic acid in first on and phenolic group in next one. So both can react with bases. Hence these are not preferable.

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