Extractants phosphorus-based

Several modifications of procedures based on halophosphonium ion have been developed. Triphenylphosphine and imidazole in combination with iodine or bromine gives good conversion of alcohols to iodides or bromides.22 An even more reactive system consists of chlorodiphenylphosphine, imidazole, and the halogen,23 and has the further advantage that the resulting phosphorus by-product diphenylphosphinic acid, can be extracted with base during product workup. 

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 ... 

One of the simplest methods of estimation of PolyPs in extracts is based on the assay of Pi, which is released from the PolyPs by hydrolysis with 1 M HC1 at 90 °C for 10 min. The Pi released under these conditions is defined as labile phosphorus . If the compounds containing organic labile phosphorus (i.e. nucleotide phosphates, sugar phosphates, etc.) were removed from the extracts by adsorption on Norit charcoal, the increase in Pj content after hydrolysis can be attributed to PolyP and pyrophosphate (PPi). Estimation of the PPj content (Mansurova, 1989) before hydrolysis may be needed in some cases for more precise calculations of the PolyP content. Pi may be determined by one of the well-known chemical methods (Fiske and Subarrow, 1925 Weil-Malerbe and Green, 1951). 

Diphosphonic acids. Phosphorus-based extractants with the structure shown in Figure 27 are known as phosphonic acids. They are highly acidic and tend to form protonated complexes. Diphosphonic acids have been studied for the extraction of tetravalent actinides such as Th . P,P -di(2-ethylhexyl)methanediphosphonic acid (H2DEH[MDP]) (see Figure 28) shows limited... 

From the knowledge of the extractant characteristics of both neutral and mono-acidic phosphorus-based organic compounds now available, it is possible to tailor-make extractants for a specifically desired separation of two metals. The present study is concerned with neutral mono-nuclear, phosphorus-based extractants for use in affecting the mutual separation of U(VI) and Th(IV). 

Liquid-liquid extraction (LLE) systems using neutral phosphorus-based organic compounds have been the subject of extensive study since Warf (1) first reported the use of tributyl phosphate, TBP, as a useful extractant for cerium(IV), uranyl and thorium nitrates. After more than twenty years, liquid-liquid extraction systems (such as the Purex and Thorex processes) employing TBP dissolved in a suitable diluent versus an aqueous HNO3 phase remain the most widely accepted systems for reactor fuel reprocessing. 

The importance of the acidic and steric properties of mono-acidic phosphorus-based extractants in the extraction of metals has been well established. The work of Mason, Peppard, et al. (2, 3) has shown that combined acidic and steric effects which result from altering the structure of the acidic extractants may be varied to give a wide range of extraction constants (Ks) for specific metals. Ks = K[H+]a/F, where Ks is a constant characteristic of the system, K is the distribution ratio, H is the hydrogen ion concentration in the equilibrated aqueous phase, F is the concentration of extractant in the equilibrated organic phase, a and b are the respective hydrogen ion and extractant dependencies. Recent studies, to be published, involving the... 

The same general method as described for the purification of the commercially obtained extractants was used to purify the neutral phosphorus-based extractants prepared in this laboratory. 

The wide range of separation factors, Ku/K h for the extraction of U(VI) and Th(IV) from 2.00 M HNO3 into eleven selected neutral phosphorus-based extractants shown in Table I, demonstrates the potential for designing extractant systems for specific metal separations. The separation factors range from 0.71 for B[DBP] to 162 for D(4-MPe-2) [iBP] a R j/K h ratio of 228. 

Table I. Extraction of Uranium and Thorium into Several Neutral Phosphorus-Based Organic Extractants from 2.00 M HNO. Extractant Solutions are 1.00 F in Dodecane...

Figure 1. Distribution ratio, K, of the extraction of U (VI) ( J) and Th (IV) (O) from 2.00M HNOs into 1.00F solutions of several phosphorus-based extractants in dodecane diluent vs. the pKA of their corresponding HDGP, HG[GP]t or H[DGP] acids (Example HDBP corresponds to TBP).

Some of the advantages of using neutral phosphorus-based organic extractants of the same general type as tributyl phosphate, TBP, designed with specially selected extraction properties in the development of LLE systems for use in reactor fuel reprocessing are ... 

Neutral or solvating carriers are commercially available phosphorus-based extractants with high selectivity toward actinides and lanthanides. Examples are presented in Table 27.2, together with the species they have been applied to. 

In our study of the extraction of the lare earths by acidic phosphorus-based extractants, we have assumed that in the extracted entity the metal is bound, in an undetermined fashion, to coordinated anions of the extractant. The extraction of the trivalent rare earth might then be represented ... 

In general, in systems employing a mono-acidic phosphorus-based extractant and which are represented by equation (4), yttrium (Z = 39) reports in the Ho (Z = 67)-Er (Z = 68) region and Sc (Z = 21) extracts with a K far greater than that for any rare earth. Consequently, separation of... 

It should be realized that the field of liquid-liquid extraction of metallic cations, basic and applied, is a very large one—even if the systems are restricted to those employing an acidic phosphorus-based extractant and the rare earths are the only metals considered. So the picture of the field presented here should not, in any sense, be considered representative. It is, rather, a reflection of our particular interests, directed by our dual love of coordination chemistry and of the rare earths. 

Another category of extractants is the neutral or solvating category. These are often phosphorus based, commonly consisting of substituted phosphine oxides or phosphate esters. Common examples applied to the extraction of U include tri-n-butyl phosphate and trioctyl phosphine oxide, whereas dibutyl butyl phosphonate has been used for the extraction of As species. They solvate the species of interest, thus making the target solute soluble in the membrane liquid phase. 

The mixture is taken up with water and the base is extracted from the toluene with dilute hydrochloric acid. The hydrochloric solution is rendered alkaline with caustic soda, the base is separated with ether, dried, and after distillation of the ether fractionated in vacuo, BP at 0.05 mm Hg, 150° to 153°C. The basic ether is then dissolved in dry ether, and ether saturated with dry hydrogen chloride is added dropwise with stirring. An excess of hydrogen chloride must be avoided as it may produce decomposition to the corresponding diphenyl ethylene. The ether-moist hydrochloride is preferably dried at once in vacuo and subsequently reprecipitated from acetone-ether and then again dried in vacuo over phosphorus pentoxide. Hydrochloride, MP 12B°C. 

This crude product is dissolved in 100 ml of dilute hydrochloric acid, the acid solution is extracted with ether, and the aqueous layer is made basic with sodium hydroxide solution (3N) in the presence of ether (approximately 250 ml). The ether layer Is separated, dried over potassium hydroxide and evaporated to a white solid. Additional purification by repeating the formation of the hydrochloric acid salt and reprecipitation of the base is carried out. When purified in this manner, followed by drying at 80°C in vacuo over phosphorus pentoxide, 2-chloro-11-(4-methyl-1-piperazinyl)dibenz[b,f] [1,4]oxazepine, li/IP 109° to 111°C, is obtained. 

For multi-analyte and/or multi-matrix methods, it is not possible to validate a method for all combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. On the other hand, the standards EN1528 andEN 12393 consist of a range of old multi-residue methods. The working principles of these methods are accepted not only in Europe, but all over the world. Most often these methods are based on extractions with acetone, acetonitrile, ethyl acetate or n-hexane. Subsequent cleanup steps are based on solvent partition steps and size exclusion or adsorption chromatography on Florisil, silica gel or alumina. Each solvent and each cleanup step has been successfully applied to hundreds of pesticides and tested in countless method validation studies. The selectivity and sensitivity of GC combined with electron capture, nitrogen-phosphorus, flame photometric or mass spectrometric detectors for a large number of pesticides are acceptable. 

Whilst carboxylic acids are readily available and inexpensive, they are relatively weak extractants and have not found much use in the recovery of base metals until recently when Versatic 10 has been piloted for the separation of Ni from Mn and Mg (Section 9.17.5.4). As with the phosphorus(V) acid extractants, the propensity for association leads to substantial levels of solvation of caboxylato... 

Methods based on flow-injection analyses have been described for the determination of extractable [62, 64-66] and available [67] phosphorus in soils. 

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