Phase transfer extraction

D.M. Roundhill, J.Y. Shen, Phase transfer extraction of heavy metals, in Calixarenes 2001, Z. Aseari, V. Bohmer, J. Haeeowfield, J. Vicens, Eds., Wuwer Acad. Publ., Dordrecht, 2001, pp. 407-420. 

The fraction of solute present in the organic phase is, therefore, 0.600. Extraction efficiency is the percentage of solute successfully transferred from its initial phase to the extracting phase. The extraction efficiency is, therefore, 60.0%. 

Although phosphine [7803-51-2] was discovered over 200 years ago ia 1783 by the French chemist Gingembre, derivatives of this toxic and pyrophoric gas were not manufactured on an industrial scale until the mid- to late 1970s. Commercial production was only possible after the development of practical, economic processes for phosphine manufacture which were patented in 1961 (1) and 1962 (2). This article describes both of these processes briefly but more focus is given to the preparation of a number of novel phosphine derivatives used in a wide variety of important commercial appHcations, for example, as flame retardants (qv), flotation collectors, biocides, solvent extraction reagents, phase-transfer catalysts, and uv photoinitiators. 

If a neutral chelate formed from a ligand such as acetylacetone is sufficiently soluble in water not to precipitate, it may stiH be extracted into an immiscible solvent and thus separated from the other constituents of the water phase. Metal recovery processes (see Mineral recovery and processing), such as from dilute leach dump Hquors, and analytical procedures are based on this phase-transfer process, as with precipitation. Solvent extraction theory and many separation systems have been reviewed (42). 

The refined grade s fastest growing use is as a commercial extraction solvent and reaction medium. Other uses are as a solvent for radical-free copolymerization of maleic anhydride and an alkyl vinyl ether, and as a solvent for the polymerization of butadiene and isoprene usiag lithium alkyls as catalyst. Other laboratory appHcations include use as a solvent for Grignard reagents, and also for phase-transfer catalysts. 

B. Tropohne. In a 1-1., three-necked, round-bottomed flask equipped with a mechanical stirrer, addition funnel, and reflux condenser are placed 500 ml. of glacial acetic acid and then, cautiously, 100 g. of sodium hydroxide pellets. After the pellets have dissolved, 100 g. of 7,7-dichlorobicyclo[3.2.0]hept-2-en-6-one is added and the solution is maintained at reflux under nitrogen for 8 hours. Concentrated hydrochloric acid is then added until the mixture is about pH 1 approximately 125 ml. of acid is required. After the addition of 1 1. of benzene, the mixture is filtered and the solid sodium chloride is washed with three 100-ml. portions of benzene. The two phases of the filtrate are separated and the aqueous phase is transferred to a 1-1. continuous extractor (Note 8) which is stirred magnetically. The combined benzene phase is transferred to a 2-1. pot connected to the extractor and the aqueous phase is extracted for 13 hours. Following distillation of the benzene, the remaining orange liquid is distilled under reduced pressure... 

The cooled mixture is transferred to a 3-1. separatory funnel, and the ethylene dichloride layer is removed. The aqueous phase is extracted three times with a total of about 500 ml. of ether. The ether and ethylene chloride solutions are combined and washed with three 100-ml. portions of saturated aqueous sodium carbonate solution, which is added cautiously at first to avoid too rapid evolution of carbon dioxide. The non-aqueous solution is then dried over anhydrous sodium carbonate, the solvents are distilled, and the remaining liquid is transferred to a Claisen flask and distilled from an oil bath under reduced pressure (Note 5). The aldehyde boils at 78° at 2 mm. there is very little fore-run and very little residue. The yield of crude 2-pyrrolealdehyde is 85-90 g. (89-95%), as an almost water-white liquid which soon crystallizes. A sample dried on a clay plate melts at 35 0°. The crude product is purified by dissolving in boiling petroleum ether (b.p. 40-60°), in the ratio of 1 g. of crude 2-pyrrolealdehyde to 25 ml. of solvent, and cooling the solution slowly to room temperature, followed by refrigeration for a few hours. The pure aldehyde is obtained from the crude in approximately 85% recovery. The over-all yield from pyrrole is 78-79% of pure 2-pyrrolealdehyde, m.p. 44 5°. 

An extensive survey has been carried out by McKervey and coworkers [7], who prepared the carbo-alkoxymethyl ethers of p-tert-h x y calix[4]arene, p-/< r/-butyl calix[6]arene, p-tert-bu y calix[8]arene, ca-lix[4]arene, calix[6Jarene, and calix[8]arene, and measured their abilities to extract cations from the aqueous phase into the nonaqueous phase. They concluded the following general aspects for the phase-transfer experiments (1) the calix[4]arene compounds show the greatest selectivity for Na (2) phase-transfer of Li is inefficient with all of the compounds (3) the calix[6]arene compounds show less affinity for Na than for K, with plateau selectivity for Rb" and Cs (4) the calix[8]ar-ene compounds are the least efficient of the cyclic oligomers, showing low levels of transport and low discrimination for all five cations (5) the calix[6]arene... 

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

A mixture of 6-mesyl-6,7-dihydro-5/f-dibenz[ ,c]azepine (29, R = Ms 13.67 g, 50 mmol) in anhyd DMSO (160 mL) and t-BuOK (18.7 g, 165 mmol) was stirred for 45 min at 20 C under N2. Another portion of /-BuOK (2.65 g, 25 mmol) was added and stirring was continued for a further 45 min. The mixture was transferred to a separating funnel with ice-cold H20 (1.1 L) and extracted with Et20 (700 mL). The aqueous phase was extracted again with Et,0 (200 mL) and the combined ethereal extracts were then dried for 2 h (CaCl2) and evaporated to give the crude product as a pale-yellow oil (9.61 g, 99 %). which was purified bv distillation (bp 125 126/0.01 Torr) to give the product as colorless crystals yield 8.25 g (85 %) mp 84-85 C. 

A suspension of lithium methoxide (prepared from 1.00 g (31.2 mmol) of methanol in 50 mL of THF and 17.7 mL (27.2 mmol) of 1.54 M butyllithium in hexane) is transferred via a cannula into a — 78 C sol ution of 5.86 g (27.1 mmol) of 2-[(/ )-(/T)-1-chloro-2-butenyl]-4,4,5,5-tctramethyl-l,3,2-dioxaborolane in 100 mL of THF. The solution is warmed, becoming homogeneous at 0 JC, and stirred for 1 h. Solvents arc removed in vacuo and the residue dissolved in 150 mL of petroleum ether (bp 40 -60 °C). This solution is washed with a citric acid/boric acid/phosphate buffer (pH 3) until the aqueous phase shows a pH of 4. The aqueous phase is extracted with 50 mL of petroleum ether (bp 40 - 60 rC). The combined organic extracts are dried over MgS04 and concentrated in vacuo to give a slightly tan oil yield 5.34 g (90%) ca. 90% ee. 

Conductor-insulator and conductor-vacuum interfaces lack a continuous exchange of free charges, and there is no electrochemical equilibrium. For this reason the work that is performed in transferring charged particles from one phase to the other is not zero. The total work, X, which must be performed by the external forces in transferring (extracting) an electron from a metal (M) into vacuum (0) is called the electron work function (or simply the work function). The work function for all metals is always positive, since otherwise the electrons would leave the conductor spontaneously. 

Apart from the study of physicochemical aspects such as ion solvation, and bio-mimetic aspects such as photosynthesis or carrier-mediated ion transfer (Volkov et al., 1996, 1998), there are several areas of potential applications of electrochemical IBTILE measurements comprising electroanalysis, lipophilicity assessment of drugs, phase transfer catalysis, electro-assisted extraction, and electrocatalysis. 

The use of tetraoctylammonium salt as phase transfer reagent has been introduced by Brust [199] for the preparation of gold colloids in the size domain of 1-3 nm. This one-step method consists of a two-phase reduction coupled with ion extraction and self-assembly using mono-layers of alkane thiols. The two-phase redox reaction controls the growth of the metallic nuclei via the simultaneous attachment of self-assembled thiol monolayers on the growing clusters. The overall reaction is summarized in Equation (5). 

Liquid-liquid extraction (also called solvent extraction) is the transfer of a substance (a consolute) dissolved in one liquid to a second liquid (the solvent) that is immiscible with the first liquid or miscible to a very limited degree. This operation is commonly used in fine chemicals manufacture (I) to wash out impurities from a contaminated solution to a solvent in order to obtain a pure solution (raffinate) from which the pure substance will be isolated, and (2) to pull out a desired substance from a contaminated liquid into the solvent leaving impurities in the first liquid. The former operation is typically employed when an organic phase is to be depleted from impurities which are soluble in acidic, alkaline, or neutral aqueous solutions Water or a diluted aqueous solution is then used as the solvent. The pure raffinate is then appropriately processed (e.g. by distillation) to isolate the desired consolute. In the latter version of extraction impurities remain in the first phase. The extract that has become rich in the desired consolute is then appropriately processed to isolate the consolute. Extraction can also be used to fractionate multiple consolutes. 

Although the Lewis cell was introduced over 50 years ago, and has several drawbacks, it is still used widely to study liquid-liquid interfacial kinetics, due to its simplicity and the adaptable nature of the experimental setup. For example, it was used recently to study the hydrolysis kinetics of -butyl acetate in the presence of a phase transfer catalyst [21]. Modeling of the system involved solving mass balance equations for coupled mass transfer and reactions for all of the species involved. Further recent applications of modified Lewis cells have focused on stripping-extraction kinetics [22-24], uncatalyzed hydrolysis [25,26], and partitioning kinetics [27]. 

As in the 1,2-dichloroethane case too, transient EMF and SHG responses to KSCN were observed for the nitrobenzene membranes without ionic sites. This suggests that here too not only SCN but also K ions are transferred into the nitrobenzene phase. Salt extraction into the bulk of the organic phase, in analogy to similar observations previously reported for neutral ionophore-incorporated liquid membranes without ionic sites [55], was indeed independently confirmed by atomic absorption spectrometry. Figure 15 shows the concentration of K in nitrobenzene equilibrated at room temperature with a 10 M aqueous solution of KSCN as a function of equilibration time. The presence of the ion exchanger TDDMA-SCN efficiently suppresses KSCN extraction into the organic phase but in its absence a substantial amount of KSCN enters the nitrobenzene phase. The trends of the EMF and the SHG responses are therefore very similar in spite of the different polarities of the plasticizers. 

Extraction of protein from aqueous solution by surfactant-containing lipophilic organic solvent (phase transfer method, or equivalently, w/o-ME-based liquid-liquid extracting, LEE). 

Higher concentrations of DMDO can be obtained by extraction of a 1 1 aqueous dilution of the distillate by CH2C12, CHC13, or CC14.88 Another method involves in situ generation of DMDO under phase transfer conditions.89... 

Classical solvent extraction is a phase transfer of solute from the solid phase to solution. All analytical extractions from solid matrices undergo three processes ... 

The efficiency of extraction is mainly dependent on temperature as it influences physical properties of the sample and its interaction with the liquid phase. The extraction is influenced by the surface tension of the solvent and its penetration into the sample (i.e. its viscosity) and by the diffusion rate and solubility of the analytes all parameters that are normally improved by a temperature increase. High temperature increases the rate of extraction. Lou et al. [122] studied the kinetics of mass transfer in PFE of polymeric samples considering that the extraction process in PFE consists of three steps ... 

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