The discovery of crown ethers.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry

Background:

• Crown ethers were discovered during research into controlling catalytic activity of vanadium and copper using multidentate ligands.
• The initial synthesis aimed to create a phenolic ligand from catechol and bis(2-chloroethyl)ether.

Purpose of the Study:

• To synthesize and characterize novel crown ether compounds.
• To investigate the complexation abilities of crown ethers with alkali metal cations.
• To explore the solubilization of inorganic salts in aprotic solvents.

Main Methods:

• Synthesis of dibenzo-18-crown-6 from catechol and bis(2-chloroethyl)ether.
• Preparation of approximately 60 related crown ether compounds with varying ring sizes and oxygen atom content.
• Investigation of complexation with sodium, potassium, and cesium cations.
• Demonstration of inorganic salt solubilization in aprotic solvents.

Main Results:

• The first crown ether, dibenzo-18-crown-6, was synthesized, exhibiting sodium cation complexation.
• Optimal polyether ring sizes were identified for different alkali metal cations (15-18 for Na, 18 for K, 18-21 for Cs).
• Crown ether complexes with cation ratios of 1:1, 3:2, and 2:1 were successfully prepared.
• Effective solubilization of inorganic salts in aprotic solvents using crown ethers was demonstrated.

Conclusions:

• Crown ethers are effective chelating agents for alkali metal cations, with size selectivity.
• The ability of crown ethers to solubilize inorganic salts has significant implications for various chemical processes.
• The discovery opened avenues for synthesizing a diverse range of macrocyclic polyethers with tunable properties.