One of the most important features of crown ethers is the formation of stable complexes with various metal salts, ammonium salts, and organic cationic compounds.With this property, various salts can be dissolved in an organic solvent. The crown ether can be chelated in the cation, and at the same time, it can form a complex due to the outward organic gene, and can also be dissolved in a non-polar organic solvent. At this time, the anion which is not solvated is present in the solvent in the form of a naked anion, so the activity is extremely large. The crown ether can dissolve the alkali metal and the organic alkali metal compound in an organic solvent. Therefore, it has found wide applications in organic synthesis, optical resolution, heavy metal chelation, separation, analysis, and physiologically active medicine and biochemistry.