Ion-pair extraction of Co(II) by crown ethers from perchlorate medium.

The extraction of cobalt(II) by chloroform solutions of the crown ethers (CE) 12C4, I5C5, 18C6, Dbl8C6, Dchl8C6 or Dch24C8 from aqueous perchlorate medium was investigated. Slope analysis of the experimental data suggested that the extraction of Co(II) by these CEs takes place through ion-pair formation, and that the chemical formula of the main extracted species is Co(OH)(+)ClO(-)(4).CE. The magnitudes of the extraction constants are in the sequence 18C6 > Dch18C6 > Dch24C8 > Db18C6 > 15C5 > 12C4, which is discussed in terms of the correspondence between the CE cavity size and the ionic radius of cobalt(II).