Solvent chelates

This sample pretreatment is devoted mainly to organic compounds that can be removed from an aqueous solution by extracting them into a water-immiscible solvent. Chelation or ion pairing between large and poorly hydrated ions and chelating agent may form neutral compounds that can be extracted by organic solvents. 

The study by several groups, most extensively by Paquette and co-workers have shown that the aqueous metal reaction also has a high diastereoselectitvity (7). The selectivity is comparable yet sometimes different from the corresponding reactions in organic solvent. Chelation-control plays an important role in the diastereoselectivity of these reactions. Even long range stereoselectivity is also possible in water (72). 

In solution, either 2 1 (Co 02)/i-peroxo complexes or 1 1 (Co 02) superoxo complexes have been formed from I or its derivatives. The product which was obtained was dependent on the temperature, solvent, chelating ligand or base which was used [40-42]. A similar complex, [4,4 -ethylenedinitrilo-2-pentanonato] cobalt(II), Co(acacen), II, forms a 1 1 superoxo complex in non-aqueous solvents containing pyridine, equation (8), at temperatures below 0 C [44]. 

As stated above, cyclopentanones, cyclobutenones, and indenes have been observed as by-products in the DBR. Wulff has studied the effect of solvent, chelation, concentration, and alkyne substitution on the product distribution. He reported that simple a,(3-unsaturated chromium carbene complexes typically show excellent selectivity for the benzannulated product. This selectivity is not sensitive to changes in solvent or substituents on the acetylene. However, the reactions of aryl complexes with acetylenes are very sensitive to the nature of both the solvent and the acetylene. For aryl chromium complexes, the highest selectivities and yields for the benzannulated product arise with solvents of low coordinating ability hexane and benzene. Solvents with intermediate coordinating ability and small size... 

The ester and catalj st are usually employed in equimoleciilar amounts. With R =CjHs (phenyl propionate), the products are o- and p-propiophenol with R = CH3 (phenyl acetate), o- and p-hydroxyacetophenone are formed. The nature of the product is influenced by the structure of the ester, by the temperature, the solvent and the amount of aluminium chloride used generally, low reaction temperatures favour the formation of p-hydroxy ketones. It is usually possible to separate the two hydroxy ketones by fractional distillation under diminished pressure through an efficient fractionating column or by steam distillation the ortho compounds, being chelated, are more volatile in steam It may be mentioned that Clemmensen reduction (compare Section IV,6) of the hj droxy ketones affords an excellent route to the substituted phenols. 

In a second attempt to extend the scope of Lewis-acid catalysis of Diels-Alder reactions in water, we have used the Mannich reaction to convert a ketone-activated monodentate dienophile into a potentially chelating p-amino ketone. The Mannich reaction seemed ideally suited for the purpose of introducing a second coordination site on a temporary basis. This reaction adds a strongly Lewis-basic amino functionality on a position p to the ketone. Moreover, the Mannich reaction is usually a reversible process, which should allow removal of the auxiliary after the reaction. Furthermore, the reaction is compatible with the use of an aqueous medium. Some Mannich reactions have even been reported to benefit from the use of water ". Finally, Lewis-acid catalysis of Mannich-type reactions in mixtures of organic solvents and water has been reported ". Hence, if both addition of the auxiliary and the subsequent Diels-Alder reaction benefit from Lewis-acid catalysis, the possibility arises of merging these steps into a one-pot procedure. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Cupferron is a ligand whose strong affinity for metal ions makes it useful as a chelating agent in liquid-liquid extractions. The following distribution ratios are known for the extraction of Hg +, Pb +, and Zn + from aqueous solutions to an organic solvent. 

A number of organic compounds, eg, acetylacetone [123-54-6] and cupferron [135-20-6] form compounds with aqueous actinide ions (IV state for reagents mentioned) that can be extracted from aqueous solution by organic solvents (12). The chelate complexes are especially noteworthy and, among these, the ones formed with diketones, such as 3-(2-thiophenoyl)-l,l,l-trifluoroacetone [326-91-0] (C4H2SCOCH2COCF2), are of importance in separation procedures for plutonium. 

Because the stmcture of 1,3-diketones comprise a methylene group between two activating carbonyls, equiUbrium is shifted toward the enol form. The equihbrium distribution varies with stmcture and solvent (303,306) (Table 13). The enol forms are cycHc and acidic and form covalent, colored, soHd chelates with metals ... 

Mineral oil and paraffins should not be used, because these are not metabolized and may irritate tissue. Various other additives are needed for stabiUty, stefihty, and isotonicity antimicrobial preservatives, antioxidants (qv), chelating agents (qv), and buffers. No parenteral container material is completely inert to parenteral solvent systems. 

Formulated metal poHshes consist of fine abrasives similar to those involved in industrial buffing operations, ie, pumice, tripoH, kaolin, rouge and crocus iron oxides, and lime. Other ingredients include surfactants (qv), eg, sodium oleate [143-19-1] or sodium dodecylben2enesulfonate [25155-30-0], chelating agents (qv), eg, citric acid [77-92-9], and solvents, eg, alcohols or aUphatic hydrocarbons. 

Metal poHshes may contain emulsifiers and thickeners for controlling the consistency and stabilization of abrasive suspensions, and the product form can be soHd, paste, or Hquid. Liquid and paste products can be solvent or emulsion types the market for the latter is growing. Formulas for metal poHshes are Hsted ia Reference 12. A representative Hquid emulsion product may contain 8—25 wt % abrasive, 2—6 wt % surfactant, 0—5 wt % chelating agents, and 0—25 wt % solvent, with the remainder being water. The abrasive content ia an emulsion paste product is greater than that ia a solvent product. 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

Many attempts have been made to reduce the ammoniacal and sulfurous odor of the standard thioglycolate formulations. As the cosmetics market is very sensitive to the presence of impurities, odor, and color, various treatments of purification have been claimed to improve the olfactory properties of thioglycolic acid and its salts, such as distillation (33), stabilization against the formation of H2S using active ingredients (34), extraction with solvents (35), active carbon (36), and chelate resin treatments (37). 

The orange-red titanium acetylacetone chelates are soluble in common solvents. These compounds are coordinately saturated (coordination number equals 6) and thus much more resistant to hydrolysis than the parent alkoxides (coordination number 4). The alkoxy groups are the moieties removed by hydrolysis. The initial product of hydrolysis is beheved to be the bis-hydroxy bis-acetylacetone titanate, (HO)2Ti(acac)2, which oligomerizes to a... 

Titanium Phosphorous Containing Chelates. The reaction of a mixture of mono (alkyl) diacid orthophosphate, di(alkyl)monoacid orthophosphate, and TiCl in a high boiling hydrocarbon solvent such as heptane, with nitrogen-assisted evolution of Hberated HCl, gives a mixture of titanium tetra(mixed alkylphosphate)esters, (H0)(R0)0=P0) Ti(0P=0(0R)2)4 in heptane solution (100). A similar mixture can be prepared by the addition of two moles of P2O5 to mole of TiCl in the presence of six moles of alcohol ... 

Capillary Electrophoresis. Capillary electrophoresis (ce) is an analytical technique that can achieve rapid high resolution separation of water-soluble components present in small sample volumes. The separations are generally based on the principle of electrically driven ions in solution. Selectivity can be varied by the alteration of pH, ionic strength, electrolyte composition, or by incorporation of additives. Typical examples of additives include organic solvents, surfactants (qv), and complexation agents (see Chelating agents). 

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