Enhanced of CsNO3 extraction in 1,2-dichloroethane by tris(2-aminoethyl)amine triamide derivatives via a dual-host strategy

A systematic study of a dual-host system exhibiting pairwise anion/cation s eparations has been performed for CsNO3 extraction. Tripodal triamides 1-4 and 9 derived from condensation of hexanoic (for 1), octanoic (for 2), deca noic (for 3), lauric (for 4), and p-tert-butylbenzoic (for 9) acid with tri s(2-aminoethyl)amine (tren) were used together with tetrabenzo-24-crown-8, a well-known Cs+ cation receptor. By using 5 mill crown ether in the organi c phase and 10 mM CsNO3 with 0.1 mM HNO3 in the aqueous phase, tripods 1, 2 , and 9 enhance CsNO3 extraction by factors of 2.4, 1.7, and 4.4, respectiv ely (for 50 mM amide concentration), while the corresponding monoamide cont rols 5-8 derived from n-propylamine (5, 6) or N,N'-dimethylethylenediamine (7, 8) and hexanoic (5, 7) or octanoic (6, 8) acid derivatives gave no sign ificant enhancement under the same conditions. This behavior may be ascribe d to nitrate complexation by the triamides, which lowers the overall thermo dynamic barrier for the salt transfer to the organic phase. The nitrate bin ding was confirmed by H-1 NMR titration of receptor solutions, using tetrab utylammonium nitrate. Association constants for the formation of the anion- nitrate complexes were found to vary between 33 and 52 M-1 for the more sol uble triamides, The synergistic effects for CsNO3 extraction are in reasona ble agreement with the values predicted theoretically from the measured ass ociation constants. Electrospray ionization mass spectrometry confirmed the predominant formation of 1:1 tripod-nitrate complexes. Monoamide controls gave no evidence of anion complexation.