How does 18-crown-6 allow potassium permanganate to dissolve in benzene?

18-crown-6 allows potassium permanganate (${\text{KMnO}}_4$) to dissolve in benzene by acting as a specialized cyclic polyether that encapsulates the potassium cation (${\text{K}}^{+}$) within its ring structure.1

The process works through the following mechanism:

• Complexation: The potassium ion fits into the central cavity of the 18-crown-6 molecule, where it is solvated by the six oxygen atoms in the ring.12
• Solubilization: The exterior of this resulting complex is masked by the nonpolar alkyl groups of the crown ether. This nonpolar exterior makes the entire complex compatible with nonpolar organic solvents like benzene.1
• Anion Transport: Because the crown ether only solvates the cation, the permanganate anion (${\text{MnO}}_4^{-}$) is dragged into the benzene solution along with the potassium complex to maintain electrical neutrality. This results in a solution often referred to as "purple benzene," where the "bare" permanganate anion acts as a highly reactive and powerful oxidizing agent.1