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12-Crown-4

12-Crown-4, also called 1,4,7,10-tetraoxacyclododecane and lithium ionophore V, is a crown ether with the formula C<sub>8</sub>H<sub>16</sub>O<sub>4</sub>. 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 LiClO<sub>4</sub> as a templating cation:

(CH<sub>2</sub>OCH<sub>2</sub>CH<sub>2</sub>Cl)<sub>2</sub> + (CH<sub>2</sub>OH)<sub>2</sub> + 2 NaOH → (CH<sub>2</sub>CH<sub>2</sub>O)<sub>4</sub> + 2 NaCl + 2 H<sub>2</sub>O

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&nbsp;Å gives it a high selectivity towards the lithium cation (ionic diameter 1.36&nbsp;Å)

Its point group is S<sub>4</sub>. The dipole moment of 12-crown-4 varies with solvent and temperature. At 25&nbsp;°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.

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)