EQUILIBRIUM ASPECTS OF THE EXTRACTION OF CESIUM 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 ethe rs dibenzo-21-crown-7 (DB21C7), bis-[4(5),4'(5')-tert-butylbenzo]-21-c rown-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 de grees 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 speci es CsBNO3 (B = crown ether) and partial dissociation to the ions CsBand NO3- in the organic phase satisfactorily account for the observed behaviour of the benzo crown ethers. However, evidence for both 1:1 an d 1:2 metal:crown complexes was obtained for DC21C7. Differences in al kylation of the benzo groups did not produce substantial differences i n the extraction behaviour of the three benzo crowns. By contrast, DC2 1C7 extracts CsNO3 much more strongly than the benzo crowns. Extractio n constants are compared with constants available from previous studie s of caesium extraction by related polyoxyethylene compounds.