Question

How would you purify the following compounds (explain what method and solvent you would use). Assume the contaminant comprises only a small percentage of the mixture.

A) decanoic acid contaminated with biphenyl

B) Biphenyl contaminated with fluorene

C) Fluorene contaminated with ethyl-4-aminobenzoate

Answer 1

a)

neutralize (mildly with Na2CO3) butanoic acid so

butanoate forms

biphenyl remain in sht eorganic layer, the aqueous acid will be soluble 100% due to ionization, then

aqueous layer = acid, organic layer = biphenyl

b)

fluorene --> use either ether , solubility is higher in ether than that of biphenyl

then, recrystallize (exploit difference in solubilty)

c)

fluoreene is very polar, ethyl-4-aminobenzoate will react with acids to form the conjguate benzoate

therefore, add mild acid, such as HCl diluted

then

ethyl-4-aminobenzoate --> goes into aqueous solution ( as a cation)