Equilibrium aspects of the extraction of caesium nitrate by dicyclohexano-21-crown-7, dibenzo-21-crown-7 and bis-[tert-alkylbenzo]-21-crown-7 in 1,2-dichloroethane

The extraction of caesium nitrate has been measured for the crown ethers dibenzo-21-crown-7 (DB21C7), bis-[4(5),4′(5′)-tert-butylbenzo]-21-crown-7 [B(tBB)21C7], bis-[4,4′-tert-octylbenzo]-21-crown-7 [B(tOB)21C7] and dicyclohexano-21-crown-7 (DC21C7) in 1,2-dichloroethane at 25 °C. Variation of the aqueous caesium nitrate concentration up to 0.4 mol dm^-3 and organic-phase crown ether concentration up to 0.025 mol dm^-3 was modelled by the program SXLSQI. Formation of the species CsBNO₃ (B = crown ether) and partial dissociation to the ions CsB⁺ and NO₃^- in the organic phase satisfactorily account for the observed behaviour of the benzo crown ethers. However, evidence for both 1:1 and 1:2 metal: crown complexes was obtained for DC21C7. Differences in alkylation of the benzo groups did not produce substantial differences in the extraction behaviour of the three benzo crowns. By contrast, DC21C7 extracts CsNO₃ much more strongly than the benzo crowns. Extraction constants are compared with constants available from previous studies of caesium extraction by related polyoxyethylene compounds.