Krzysztof E. Krakowiak

Industrial applications of molecular recognition technology to separations of platinum group metals and selective removal of metal impurities from process streams

Green chemistry procedures using a novel process based on molecular recognition principles are described for the selective separation and recovery of metals in industrial processes. This process, termed molecular recognition technology (MRT), has the capability to make selective separations at various stages in metal life cycles. Results are given for individual platinum group metal separations, recycling of palladium from end-of-life products, copper purification by control of impurity bismuth concentration levels, and purification of H2SO4 for use in health-related applications by Hg removal to 0.1 mg L−1 concentration levels. In each case, the metals are selectively separated in pure form and can be recovered for reuse or environmentally safe disposal. High metal selectivity is obtained using a pre-designed ligand bonded chemically by a tether to a solid support, such as silica gel. Separations are performed in column mode using feed solutions containing the target metal in a matrix of acid and/or other metals. The target metal is selectively separated by the silica gel-bound ligand, leaving other solution components to go to the raffinate, where individual components can be recovered, if desired. Minimal waste is generated. Elution of the washed column with a small volume of eluent produces a concentrated eluate of pure target metal, which is easily separated in pure form. The MRT process uses innocuous wash and elution chemicals and no solvents. Metal recovery rather than dispersal into the commons is essential from a metal sustainability standpoint. A major benefit of metal recycling is reduction in the amount of virgin ore that must be mined to replace discarded metals. As metal use increases, conservation of this valuable metal resource increases in importance. Metal recycling rates are generally low. From end-of-life high-tech electronic products, they are in the 1–5% range. Separation and recovery results presented here show that green chemistry MRT processes have great promise in increasing metal sustainability in industrial processes.

Approaches to improvement of metal ion selectivity by cryptands

Abstract Several approaches to improvement of metal ion selectivity by mixed oxygen–nitrogen donor cryptands are discussed. Because of the relatively rigid structures of cryptands, thermodynamic stabilities of the cryptate complexes strongly depend on the match of the cation size and cryptand cavity diameters. Symmetry is an important factor influencing the properties of cryptand complexation. One rule to improve metal ion selectivity by oxygen–nitrogen donor cryptands is to obtain the ligand that has the best size-match cavity with the cation while keeping a symmetric spherical-coordination array. High selectivity for a small cation can be obtained when the cryptand is able to form a number of six-membered chelate rings with the metal ion while the requirements of the high-symmetric donor atom array and size-matched cavity are met. On the other hand, introduction of benzene rings and other groups to cryptands usually decreases metal ion binding and selectivity.

Macrocycle-metal cation interactions involving polyaza macrocycles bonded to silica gel via a nitrogen donor atom

Macrocycles are noted for the remarkable selectivities which certain of them show toward metal ions. This selectivity has been studied extensively for free macrocycles in single solvent systems. However, there is a need for new systems that are more economical and with engineering feasibility which incorporate macrocycles to perform actual separations. Stable silica gel-bound macrocycles maintain the macrocycle for reuse in performing actual separations. The polyaza macrocycles 1,4, 7,10-tetraaza-18-crown-6, pentaaza-15-crown-5, and hexaaza-18-crown-6 have been synthesized with the macrocycle covalently bonded to silica gel via one of the nitrogen donor atoms. These bound macrocycles have selective and strong interactions with the soft heavy metal cations as well as proton chemistry which have now been quantified by the measurement of equilibrium constants. These interactions are similar to those of the analogous unbound macrocycles. Separations of ppb levels of heavy metal cations from concentrated matrices of other cations such as the alkali and alkaline earth cations have also been made. The bound macrocycles apparently show a greater tendency towards cavity size-based selectivity than the analogous unbound ligands. This is presumably due to increased ligand rigidity caused by the donor atom attachment to the solid support.

Convenient syntheses of N-[2-(2-hydroxyethoxy)ethyl]-substituted polyaza-crown ethers and cyclams without the need for a hydroxy blocking group

Abstract Short three or four step syntheses of N-[2-(2-hydroxyethoxy)ethyl]-substituted polyaza-crowns and cyclams without the need for a hydroxy blocking group are presented. Cyclization of a hydroxy-substituted diamine took place on the two amine nitrogen atoms because sodium carbonate does not ionize the hydroxy group.

Thermal Removal of Boc-Protecting Groups During Preparation of Open-Chain Polyamines

Abstract Per-N-tosylated 3,8-diaza-1,10-decanediamine (9), 4,9-diaza-1,12-dodecanediamine (spermine) (10) and 3,6,9,14,17,20-hexaaza-1,22-docosanediamine (11) were prepared by treating mono-BOC-protected, per-N-tosylated 1,2-ethanediamine (5), 1,3-propanediamine (6) and triethylenetetraamine (7), respectively, with 1,4-dibromobutane and removing the BOC-protecting groups at 100–120 °C.

New high yield syntheses of cyclams using the crab-like cyclization reaction

Abstract A new high yield method to synthesize cyclams containing one or two unsubstituted ring nitrogen atoms and with alkyl groups on the remaining ring nitrogen atoms is presented. The method consists of the ring closure reaction of a crab-like bis -α-chloroamide with a bis -secondary amine followed by reduction. The amide functions of the starting material act as protecting groups for the protons on the amide nitrogen atoms.

Synthesis of macrocyclic acetals containing lipophilic substituents

Abstract A series of new macrocyclic acetals all containing lipophilic substituents were prepared by reacting the appropriate diols and lipophilic acetal-containing dichlorides or ditosylates. The reactions using the ditosylates gave the best yields. Several of the macrocycles contained pyridine subcyclic units. The lipophilic acetals were obtained by reacting a long-chain aldehyde with 2-hydroxyethyl chloride or tosylate and 3-hydroxypropyl chloride or tosylate. At least two of the new pyridino ligands complexed with metal ions as shown by the use of these materials as carriers for silver nitrate through a water-methylene chloride-water bulk liquid membrane system.

Syntheses and aggregate study of bisphenol-containing diaza-18-crown-6 ligands

Abstract Bisphenol-containing diaza-18-crown-6 ligands (1–16) were synthesized as potential membrane-forming amphiphilesvia the one-pot Mannich reaction. Sonication of the crude products in a small amount of MeOH followed by filtration and drying proved to be an efficient method of purifying nearly all compounds. Compounds8 and9 were selected for assay as amphiphiles. Compared to simple, alkylated diazacrown ethers, the stability of the amphisomes formed from these monomers is lower possibly because intramolecular hydrogen bonding prevents formation of intermolecular hydrogen bonds. Bisphenol-containing diaza-18-crown-6 ligands (1–16) were synthesized as potential membrane-forming amphiphiles. Download : Download full-size image

Syn-bishydroxymethyl-14-crown-4: A possible pre-organized molecule for simultaneous lithium complexation and anion solvation

Abstract The synthesis and molecular structure of syn-6,13-bishydroxymethyl-14-crown-4 is reported. Conformational analysis reveals that the gauche arrangement between the ethereal oxygens (-O-CH 2 CH 2 -O- units) is the preferred conformation. The CH 2 OH groups bonded to the ring, point away from the cavity and have a syn relationship. The synthetic route is elucidated by the crystal structure of 6,13-dimethylenyl-14-crown-4-LiSCN complex.

Novel syntheses of monofunctionalized triaza-crowns and cyclams with a secondary amine group on a side chain

Abstract Several monofunctionalized triaza-crowns and cyclams each containing a secondary amine group on a side chain have been prepared in good yields in few steps from readily available starting materials. The X-ray crystal structure of the complex of silver ion with 1-(2-ethylamino)ethyl-4,7,10,13-tetraethyl-1,4,7,10,13-pentaazacyclopentadecane (4) shows that the nitrogen atom of the side chain interacts strongly with the silver ion.