Neutral extractants

Neutral Extractants. Many neutral organophosphoms extractants are available phosphate esters, phosphonate esters, phosphinate esters, and phosphine oxides. The most popular neutral extractant is tributylphosphate (TBP), which reacts with RE elements according to a solvation mechanism ... 

An alternative to the formation of neutral metal chelates for solvent extraction is that in which the species of analytical interest associates with oppositely charged ions to form a neutral extractable species.6 Such complexes may form clusters with increasing concentration which are larger than just simple ion pairs, particularly in organic solvents of low dielectric constant. The following types of ion association complexes may be recognised. 

Neutral catalysts, in phenolic resin polymerization, 18 761—762 Neutral extractants, of rare-earth elements, 14 642... 

Erikson and Pellizari [75] applied gas chromatography to show that neutral extracts of sewage sludge contained appreciable amounts of polychlorobiphenyls (Table 5.4). 

Table 5.4 Quantitation of PCBs in hexane eluate of neutral extract of sewage sludge... 

The salient features of the GC-MS data for the neutral extract components separated from PCB contaminated sediment in New Bedford harbor, Massachusetts are given in Fig. 16. The TIC trace indicates a major UCM with super-... 

FIGURE 8 HPLC chromatogram of a tablet extract of an OTC product from natural material showing many natural components including active ingredient (peaks labeled A ), preservatives P and degradants D . Note that Peak A2 was found to hydrolyzed into D under neutral extraction conditions and component D was found to be retained by Nylon filters. 

Thus there is considerable incentive to find extractants that could tolerate higher quantities of solids in H2SO4 leach liquors. Stripping of uranium from the Amex process extractant and subsequent regeneration of the amine solvent also consume considerable quantities of acid and base. Recovery of uranium from H2SO4 solutions would be simplified if a convenient neutral extractant could be found. An extractant with better selectivity for vanadium and molybdenum than HDEHP and long-chain amines is also desirable. 

Treated soils undergo a volumetric increase of approximately 120%. Thus, the total treated waste may not be able to be placed back into the original excavation. The cost for removal to a landfill or other area could be substantial. Organic contaminants, including volatiles and base/neutral extractables are not immobilized to any significant extent. The vendor is no longer in business, and it is not known if the technology is currently commercially available. 

Samples were taken at different intervals, neutralized, extracted and acetylated for H NMR analyses. The coefficients of the integrals of the aliphatic (62.0-2.2) and the aromatic (62.3-2.5) acetoxy groups of the proton NMR spectra, were taken as the yields of hydroxymethylation. 

McFall JA, Antoine SR, DeLeon IR. 1985. Base-neutral extractable organic pollutants in biota and sediments from Lake Pontchartrain. Chemosphere 14(10) 1561-1569. 

To methylenecyclohexane (0.96 g. 10 mmol) in CH2C12 (20 mL) was added at 0 C with stirring dimethyl(methylsulfanyl)sulfonium tetrafluoroborate (2.16 g, 11 mmol) and stirring was continued for 20 min. Afterwards, a slight excess of Et3N 3HF (2.4 g, 15 mmol) dissolved in CH2C12 (10 mL) was added dropwise at 0 "C and the mixture was stirred for a further 3 h at rt. The mixture was then poured onto ice water, neutralized, extracted, dried, and the solvents evaporated to give the crude title compound yield 1.54 g (95%) bp 72-73 C/l 5 Torr. 

No sample fractionation procedure is given in the protocol, but several possible techniques were included in the literature review, including acid/base-neutral extraction, solvent fractionation (8), column chromatography, TLC, and HPLC (presented elsewhere in this chapter). 

The concentrated extract is then split. To one portion, 1.0 mL of DMSO is added, and the dichloromethane is removed under a stream of nitrogen. The resulting DMSO solution is used for the direct assay of the extract. If fractionation of the remaining extract is required, the investigator is given the option of using the acid/base-neutral extraction scheme described in step 3 of the nonaqueous liquid protocol or the HPLC technique described in the sample fractionation methods section. 

The second series of methylene chloride extractions was accomplished by the addition of 300 mL of solvent to the aqueous layer, homogenization for 1 min, then pH adjustment to <2 via the addition of 6.0 N hydrochloric acid. Following an additional homogenization for 1 min, the suspension was centrifuged and processed as for the base-neutral extractions. The extrac-... 

Gaseous hydrogen chloride is bubbled through a solution of 0.8 g of 22,23-dibromoergost-8(14)-en-3/ -yl acetate in 25 ml of chloroform at 0° for 2 hr. The solvent is removed by evaporation and the solid mixture of A8(14>- and A14 -isomers is hydrogenated over platinum oxide (0-2 g) in ether (100 ml) and ethyl acetate (100 ml). The reaction mixture is filtered, evaporated, and the residue treated in the cold with 10 ml of acetic anhydride and 10 ml of concentrated sulfuric acid. This mixture is shaken for 5 min and 10 ml of water is added carefully. After neutralization, extraction and recrystallization the 14oc-product is obtained in 30-35 % yield.30... 

Among the neutral extractants, alcohols, ethers, and ketones have been used extensively. The most fatuous example of these is the extraction of uranyl nitrate into diethyl ether, the process used in the Manhattan Project to purify the uranium... 

The most widely used neutral extractants, however, are the organophosphoms compounds, of which the ester, TBP, is the most important. TBP forms complexes with the actinide elements thorium, uranium, neptunium, and plutonium by bonding to the central metal atom via the phosphoryl oxygen in the structure... 

In the case of anionic chelating extractants such as HDEHP, HDBP, HTTA or generally HA, the reaction stoichiometry with respect to the metal, Mz+, and extractant, HA, is given by equation (134). In this case, DM is given by equation (135),90 where [MAJ is the neutral extracted species and [MA ] represents all the aqueous phase species for n = 0-N of which MAX is one. A plot... 

Recently, another class of neutral organophosphorus compounds, namely, N,N-dialkyl carbamoyl methyl phosphonate (CMP) (59) and its phosphine oxide analog (CMPO) have received attention due to their ability to extract even trivalent actinides from acidic solutions along with the hexa- and tetravalent actinide ions. These biden-tate phosphorus-based neutral extractants are reported to be stronger extractants as compared to TOPO (59-62). Pu(IV) and U(VI) are extracted as per the following extraction equilibria ... 

Srinivasan, T.G. Suresh, A. Prasanna, R. Jayanthi, N. Vasudeva Rao, P.R. Metal-solvate stoichiometry evaluation in extractions by solvating type neutral extractants -A novel approach, Solvent Extr. Ion Exch. 14 (1996) 443-458. 

---