12-Crown-4
# 12-Crown-4

12-Crown-4, also called 1,4,7,10-tetraoxacyclododecane and lithium ionophore V, is a crown ether with the formula $C_8H_{16}O_4.$ 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 $LiClO_4$ as a templating cation:

    $(CH_2OCH_2CH_2Cl)_2$ + $(CH_2OH)_2$ + 2 NaOH → $(CH_2CH_2O)_4$ + 2 NaCl + 2 $H_2O$

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 $S_4.$ 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.

