Glen A. Clark

Macrocycle-Facilitated Transport of Ions in Liquid Membrane Systems

Abstract Ion transport in various liquid membrane systems is discussed in terms of those factors which create the environment for efficient and selective transport. The following parameters which affect ion transport are discussed: membrane configuration, cation-macrocycle complex stability, macrocycle partitioning between membrane and water phases, proton ionization of acidic macrocycles, macrocycle concentration, anion type, ion concentration, membrane solvent type and receiving phase composition. A summary of existing models of ion transport is given along with possible applications to macrocycle-facilitated liquid membraneion transport.

Proton-ionizable crown compounds : 5. Macrocycle-mediated proton-coupled transport of alkali metal cations in H2OCH2Cl2H2O liquid membrane systems

Abstract Alkali cation transport is studied using proton-ionizable macrocycle carriers of the 4-hydroxypyridine and pyridone types in a bulk H 2 OCH 2 Cl 2 H 2 O liquid membrane system as a function of source and receiving phase pH. A pyridone crown-6 type macrocycle containing an octyl substituent (3) transports Li + , Na + , K + , Rb + and Cs + from MOH solutions by a proton-coupled mechanism in which no co-anion is transported. In these cases, alkali cation transport increases exponentially with increasing source phase pH above pH 12. Generally, alkali cation transport at source phase pH 14 is higher when nitric acid is present (receiving pH = 1.5) than when it is absent. In competitive transport experiments with macrocycle 3 involving K + ) and one other alkali cation M + , K + is transported selectively over M + by 4.6 (Na + ), 2.7 (Rb + ) and 6.3 (Cs + ) fold when the source and receiving phase pH values are 14 and 7, respectively.

Transport of AgBr2−, PdBr4 2−, and AuBr4- in an Emulsion Membrane System Using K+-Dicyclohexano-18-crown-6 as Carrier

Abstract Silver, palladium, and gold have been transported through a 1.5 M KBr/toluene/0.025 M MgS2O3 (or Mg(NO2)3) emulsion membrane system as AgBr2 −, PdBr4 2− and AuBr4, respectively, using K+-dicyclohexano-18-crown-6(DCl8C6) as carrier. The transport studies are carried out in AgBr2 −, PdBr4 2−, and AuBr4 − single solutions and in AgBr2−/PdBr4 2−, AgBr2−/AuBr4 −, and PdBr4 2−/AuBr4 − binary solutions. The presence of DC18C6 in the toluene membrane is found to greatly enhance ion transport. When MgS2O3 is in the receiving phase, AuBr4 - is found to transport well even without DC18C6 in the membrane. The transport of AgBr2 −, PdBr4 2−, and AuBr4 − is greater for those systems containing MgS2O3 in the receiving phase than for those with Mg(NO3)2. In binary studies with MgS2O3 in the receiving phase, PdBr4 2− is transported selectively over AgBr2 − and AuBr4 − is transported selectively over either PdBr4 2− or AgBr2 −.

Transport of AgBr2− in an emulsion liquid membrane using Mn+—DC18C6 carriers (Mn+ = Li+, Na+, K+, or Mg2+)☆

Silver transport, as AgBr2−, has been investigated in emulsion liquid membranes. In accordance with the requirements of electrical neutrality, this anion accompanies a diffusing cation—macrocycle complex across the organic membrane. An excess of MBrn (Mn+ Li+, Na+, K+, Mg2+) is added to aqueous AgNO3 to form source phase solutions consisting of Mn+, Br−, NO3−, and AgBr2-. The organic membrane is composed of a solution of DC18C6 in toluene. An aqueous solution of Li2S2O3 is used as the receiving phase because of the ability of S2O32− to strip the Ag+ from the AgBr2− at the membrane/receiving phase interface. The quantity of AgBr2− transported depends on the metal ion present and decreases in the order K+ > Na+ > Li+ > Mg2+ in accordance with the decrease in log K values for Mn+—DC18C6 interaction.

Log K, ΔH, and TΔS values for the reaction of several uni- and bivalent metal ions with several unsubstituted cyclic polyethers and their benzo-substituted derivatives

Abstract Log K, ΔH, and TΔS values valid in methanol at 25 °C have been determined calorimetrically for the interaction of several uni- and bivalent metal ions with benzo-15-crown-5 (B15C5), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), dibenzo-21-crown-7 (DB21C7), dibenzo-24-crown-8 (DB24C8), and dibenzo-27-crown-9 (DB27C9). In addition, log K, ΔH, and TΔS values have been determined under the same conditions for interactions of Tl+ with 15-crown-5 (15C5), 18-crown-6 (18C6), and 21-crown-7 (21C7) and for interactions of Pb2+ with 15C5 and 21C7. For the interaction of a given cation with large ring macrocycles, e.g., DB24C8 and DB27C9, log K values are usually lower than with macrocycles whose cavity radius closely matches the cation radius. Generally, log K and - ΔH values decrease in the series un-, monobenzo-, dibenzo-substituted macrocycle. Log K values decrease in this series more for bivalent than for univalent cations.

Effect of co-anion on DC18C6-mediated Tl+ transport through an emulsion liquid membrane

Emulsion membrane systems consisting of an aqueous thallous salt source phase, a toluene membrane containing the macrocyclic ligand dicyclohexano-18-crown-6 (DC 18C6)(0.02M), the surfactant Span 80 (sorbitan monooleate) (3% v/v), and an aqueous 0.01M Li4P2O7 receiving phase were studied with respect to the disappearance of Tl+ from the source phase as a function of time. The salts TlOH, Tl2 CO3, TlAu(CN)2, TlSCN, TlClO4, TlAg(CN)2, Tl4 Fe(CN)6, TlF, Tl2SO4, TlBr, CH2 (COOTl)2, HCOOTl, TlCl, and TlNO3 were investigated singly (salts listed in order of decreasing total percentage of Tl+ transport observed). In competitive transport experiments using equimolar TlAg(CN)2 and TlAu(CN)2, TlAu(CN)2 was found to transport by a factor of six over TlAg(CN)2. Attempts are made to explain the co-anion effect on Tl+ transport by relating transport inversely to the negative free energy of hydration of the co-anion, directly to the amount of ion pairing of the co-anion with a cationic species present, and directly to the amount of deprotonation of the surfactant.

Cation transport at 25°c from binary Tl+Mn+ and K+Mn+ nitrate mixtures in a H2OCHCl3H2O liquid membrane system containing a series of macrocyclic polyether carriers☆

Abstract Carrier-mediated cation fluxes were determined using a H 2 OCHC1 3 H 2 O liquid merebrane system for TlNO 3 and for binary mixtures of either TlNO 3 or KNO 3 with alkali metal ions, alkaline earth metal ions, and Pb 2+ (in the case of TlNO 3 ). Both macrocyclic polyether and cryptand ligands were used as carriers. In Tl + M n + mixtures, selective transport of Tl + was found over all cations studied, except in the cases of Ag + by 2.2 and of Pb 2+ by 18C6, DC18C6, ClDKP18C6, and 2.2. Generally, K + was transported selectively from K + M n+ mixtures, except in the cases of K + Tl + mixtures in which Tl + was transported selectively in all cases. A model relating cation flux to log K (CH 3 OH) for M n + —macrocycle interaction and to ion-partitioning between the organic and aqueous phases was successful in rationalizing selective cation transport in most of the systems studied.

Effect of Macrocycle Type on Pb2+ Transport through an Emulsion Liquid Membrane

Abstract The relative effectiveness of 14 different macro-cycles in transporting Pb(NO3)2 has been determined at 25 °C using a water-toluene-water emulsion membrane system. The largest amount of Pb2+ transport was found with dideeyl-1,1O-diaza-18-crown-6 (91%), followed by dicyclohexano-18-crown-6 (81%), di-tert-butyl-dicyclohexano-l8-crown-6 (77%), 1,10-diaza-18-crown-6 (27%), and cryptand 2.2.1 (4,7,13,16,21,24-pentoxa-1,10-diazabicyclo(8, 8, 5)-tricosane) (16%). The use of the other macrocycles produced little Pb2+ transport. Analysis of the transport results shows that, for most effective transport, the macrocycle should distribute preferentially to the organic phase and the log K value for the binding of the macrocycle with Pb2+ must be large enough for quantitative extraction of the Pb2 + into the membrane. However, this log K value must be sufficiently smaller than that for interaction of Pb2+ with P2O7 4−, the receiving phase complexing agent, to allow a large Pb2+ concentration gradient to be est...

Solvent Extraction of the Nitrate Salts of K+, Ag+ TI+ and Pb2+ Using Di(2-Ethylhexyl) phosphoric Acid and Dicyclohexano-18-Crown-6 in Toluene

Abstract A solvent extraction system is used to determine metal distribution coefficient, D n+, values between water and toluene for the nitrate salts of K+M, Ag+, T1+, and Pb2+ using, both individually and together, the organic soluble complexing agents HDEHP and DC18C6 (Figure 1). Synergistic solvent extraction effects.are found for all of the metals examined. The extraction of Pb2+ is much greater than that of the monovalent cations. The extraction of K+ increases either as the equilibration temperature decreases or as the equilibrated aqueous pH increases. The extraction of Ag+ increases in a regular fashion until the initial concentration of DC18C6 in the toluene reaches the initial concentration of HDEHP+in the toluene. Beyond this point, no appreciable increase in Ag+ extraction is observed with increased initial DC18C6 concentration.

Macrocycle-Mediated Transport in a Bulk 1.5 M HNO3-CHCI3-0.01 M HNO3 Membrane System of Pd2+ and Mn+ from Pd2+Mn+ Mixtures

Abstract Pd2+ has been transported using sulfur substituted macrocycles as carriers and several Mn+ (Mn+ = Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Ag+, TL+, Cd2+, and Pb2+) have been transported using 18-crown-6 (18C6) and sulfur substituted macrocycles as carriers in a 1.5M HN03/CHCL33/0.01M HNO3 bulk liquid membrane system. Competitive Pd2+-Mn+ transport studies have also been carried out for the same systems. The cyclic polyether 18C6 transports Mn+ selectively over Pd2+ for all Mn+ except Li+, Mg2+, and Cd2+. In the cases of these three cations, no transport was found for either Pd2+ or Mn+. Generally, the sulfur substituted macrocycles transport Pd2+ selectively over Mn+.