12-Crown-4 Explained

12-Crown-4, also called 1,4,7,10-tetraoxacyclododecane and lithium ionophore V, is a crown ether with the formula C₈H₁₆O₄. It is a cyclic tetramer of ethylene oxide which is specific for the lithium cation.

Synthesis

12-Crown-4 can be synthesized using a modified Williamson ether synthesis, using LiClO₄ as a templating cation:^[1]

(CH₂OCH₂CH₂Cl)₂ + (CH₂OH)₂ + 2 NaOH → (CH₂CH₂O)₄ + 2 NaCl + 2 H₂O

It also forms from the cyclic oligomerization of ethylene oxide in the presence of gaseous boron trifluoride.

Properties

Like other crown ethers, 12-crown-4 complexes with alkali metal cations. The cavity diameter of 1.2-1.5 Å gives it a high selectivity towards the lithium cation (ionic diameter 1.36 Å)

Its point group is S₄. The dipole moment of 12-crown-4 varies with solvent and temperature. At 25 °C, the dipole moment of 12-crown-4 was determined as 2.33 ± 0.03 D in cyclohexane and 2.46 ± 0.01 D in benzene.^[2]

References

• Sigma-Aldrich Handbook of Fine Chemicals, 2007, page 768.
• Sigma-Aldrich Cyclic tetramer of ethylene oxide which is specific for the lithium cation. 98%, 2018

See also

• Crown ether
• Cyclen, a similar molecule with N atoms (aza groups) instead of O atoms (ethers)

Notes and References

1. Cook. Fred L.. Caruso. Thomas C.. Byrne. Michael P.. Bowers. Chauncey W.. Speck. Don H.. Liotta. Charles L.. 1974. Facile syntheses of 12-crown-4 and 15-crown-5. Tetrahedron Letters. en. 15. 46. 4029–4032. 10.1016/S0040-4039(01)92075-1.
2. Caswell. Lyman R.. Savannunt. Diana S.. Temperature and solvent effects on the experimental dipole moments of three crown ethers. Journal of Heterocyclic Chemistry. January 1988. 25. 1. 73–79. 10.1002/jhet.5570250111.