Halide complexes, solvent extraction

Halides other than fluoride form very weak complexes in aqueous solution there are no reliable equilibrium constants to be found in the literature. The solution chemistry of aqueous solutions of beryllium chloride, bromide, and iodide have been reviewed previously (9). Some evidence for the formation of thiocyanate complexes was obtained in solvent extraction studies (134). 

This is the most common route to vinylidene complexes and occurs in reactions of the 1 -alkynes with metal complexes, preferably with labile neutral or anionic ligands, which give neutral or cationic complexes, respectively. In the latter case, halide is commonly extracted, either by spontaneous displacement by a polar solvent, or by using sodium, silver or thallium salts. 

P-Diketonates. Very strong actinide complexes with p-diketones [An(acac)4 and An02(acac)2] are used in solvent extraction and separation of actinides. They are prepared by direct interaction of the metal or actinyl halide with the appropriate p-diketone in the presence of a base. Only fluorinated An(IV) diketonates produce adducts with Lewis bases, whereas common An02(acac)2 (An = Np, Pu) are stabilized by adduct formation. Fluorinated U02(hfa)2 is a very strong Lewis acid and its adducts with H20 and ROH can be sublimed without decomposition [282],... 

A number of main group and transition metal dithiocarboxylates have been described. They are commonly prepared by metathesis between alkali metal dithiocarboxylates and metal halides. Heavy metal derivatives usually precipitate from aqueous solutions, but are soluble in organic solvents and can be solvent extracted. The alkali metal, ammonium, phosphonium, and arsonium salts are water soluble.300 The composition of metal complexes is sensitive to preparation conditions and is frequently pH dependent. 

Basic dyes (triphenylmethane, xanthene, azine, etc., dyes) form ion-association compounds (ion-pairs) with anionic halide complexes of metals and non-metals e.g., SbCl, AuBr4 , TaFe , BF4 ). The resulting compounds, that may be extracted into non-polar organic solvents, may serve as a basis for sensitive spectrophotometric methods [62-65]. 

Copper can be determined by use of ion associates, formed by the cationic complexes of Cu(I) with cuproine [63-65], neocuproine [65], bathocuproine [66] and thio-crown ethers [67,68], associated with the acid dyes such as Rose Bengal (e = 7.8-10 ) [63,65,66], the ethyl ester of eosin (e = 9.4-10 ) [64], and Erythrosin [63]. These ion-associates are extracted into chloroform [65,66], 1,2-dichloroethane [64,67,68], and other solvents. The ion-associates of cyanide [69] and chloride [70,71] complexes of Cu(I) with Methylene Blue (1,2-dichloroethane, = 9.8-10 ) [69], and Ethyl Violet (toluene, = 9.6-10 ) [70] are also worth mentioning. The halide complexes of Cu(I) with azo dyes have also been extracted. 

This methodology enjoys the merits of other approaches and exhibits several additional advantages 1) it has proven applicable to a wide range of transition metal and main group oxides 2) the metal precursors studied so far are readily available, being either alkoxide or halide complexes 3) in many cases, syntheses can be run in alcoholic solvents in essentially nonhydrolytic conditions, which aids in controlling hydrolysis and condensation rates 4) the critical micelle concentrations required for polyethylene-oxide-polypropylene-oxide di- and triblock copolymers are usually much lower than the concentrations needed for ionic surfactants and 5) because of the neutral, nonaqueous conditions used in these preparations, control of pH is not required, and the surfactant can be removed from the mesostructured material by calcination or milder solvent extraction methods with nonpolar solvents. 

One field of using coordination chemistry approaches is the solvent extraction of halide complexes of metals. 

Zolotov,Yu.A. Iofa,B.Z. Chuchalin,L.K. Solvent Extraction of Metal Halide Complexes Nauka Publishing House Moscow, 1973 (in Russian). 

The very simple macrocycle, the easy-to-prepare system meso-octamethylcalix[4]pyrrole 3, which has been already mentioned in this chapter, can act as both a cation (Cs+) and an anion (Cl or Br ) receptor forming a complex of 1 1 1 cesium calix[4]pyrrole halide stoichiometry, under conditions of aqueous nitrobenzene solvent extraction (Figure 25). Control studies involving nitrate revealed no evidence of ion pairing for CSNO3 under conditions identical to those where it was observed for CsCl and CsBr, thus enlightening the high selectivity of the process. 

Several solvent uses have been proposed. Dimethyl sulfate has been used as a solvent for the study of Lewis acid—aromatic hydrocarbon complexes (148). It also is effective as an extraction solvent to separate phosphoms halide—hydrocarbon mixtures and aromatic hydrocarbons from aliphatics, and it acts as an electrolyte in electroplating iron (149—152). The toxicity of dimethyl sulfate precludes its use as a general-purpose solvent. 

The above characterizations primarily concern the interactions between molecular solutes and ILs. However, ILs are also good solvents for ionic compounds, and have been studied extensively as media for transition metal catalysis [4, 38, 219] and for the extraction of heavy metals [23]. ILs are capable of solvating even simple salts, such as NaCl, to some degree [219], and in fact the removal of halide impurities resulting from synthesis can be a considerable challenge [68]. However, ionic complexes are generally far more soluble than simple salts [220], and we focus our attention on these systems as they have received greater study and are more relevant to the processes noted above. 

The alkylated BDHC complexes are very unstable in general and cannot be isolated in pure form from the reaction mixture. A large portion of an alkylated product decomposes during the extraction procedure with organic solvents. Thus, the decomposition behavior of the alkylated BDHC complexes was investigated as they were prepared in aqueous media, after decomposition of the excess NaBH4 with acid in the presence of excess alkyl halide. An alkylated BDHC complex also can be prepared by the reaction of [Co(II)(BDHC)]C104 with an alkyl iodide under alkaline condition (pH 12) the disproportionation reaction yields the Co(III)(BDHC) species and an alkylated BDHC complex. 

The allylmagnesium halide in ether is slowly added to a suspension or solution of the metal halide at 0°C or lower. Addition at low T improves yields and is essential for the synthesis of thermally unstable, homoleptic allyl complexes. The complexes are isolated by evaporation of the reaction mixture and extraction into an aromatic or alkane solvent. Purification is effected by crystallization or sublimation. When stable allyl compounds are prepared, an aqueous wash of the reaction mixture can be used to remove Mg salts and xs RMgX or -Li reagent the crude products can then be isolated from the resultant organic layer. 

The most generally applicable method of forming the transition- and inner transition-metal 7t-cyclopentadienyl bond involves the reaction of Na[Cp] with the appropriate anhydrous metal halide or complex halide in an ethereal solvent such as THF or glyme under a dry, inert atmosphere. The complexes are usually isolated by evaporation of the solvent and extraction into an aromatic or aliphatic hydrocarbon solvent. Purification is achieved by crystallization or sublimation. 

A number of elements give anionic complexes with halide and other ligands. These complexes can form ion-associates (ion pairs) with basic dyes, and are extractable into nonpolar solvents. The extracts form the basis of sensitive extraction-spectrophotometric methods [68,69]. 

Palladium and thio-Michler s ketone (TMK) (formula 46.2) form red mixed ligand complexes Pd(TMK)2X2 (X = CF, Br, T, or SCN ) on extraction with CHCI3, in the presence of suitable halide ions in weakly acidic aqueous solution. The complexes [Pd(TMK)4(Sol)2] are formed when the extraction is done with mixtures of CHCI3 with a polar solvent (Sol) such as ethanol or DMF, or with only a polar solvent, e.g., amyl alcohol. Similar complexes (Pd TMK = 1 4) form in mixed organic-aqueous solutions containing 30-40% of DMF or 40-50% of ethanol. 

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