Synergistic reagents

Althongh most acidic extractants other than the phosphorns acids extract nickel before cobalt the separation factors are not snfficiently high so it is difficult to carry out an effective separation. Therefore, several synergistic reagent mixtures have been developed at MINTEK to separate nickel from cobalt. These mixtures include monoxime/carboxylic acid, pyridine carboxylate ester/carboxylic acid, and pyridine carboxylate ester/phosphorous acids. However, the indnstry seems reluctant to nse synergistic mixtnres, probably because of problems associated with precise control of the ratio of extractants in the organic phase to maintain synergism. 

The oxidation reaction proceeds to completion within 30 to 40 min the oxidant consumed is precisely determined on an excess of reagent by means of an iodometric procedure. Polyethylene samples containing varying amounts of 4,4/-thiobis(6-f-butyl-m-cresol) and other synergists were analysed with results close to the expected values. The method has been applied to numerous commercially available polymers. 

These equations do not provide complete definition of the reactions that may be of significance in particular solvent extraction systems. For example, HTTA can exist as a keto, an enol, and a keto-hydrate species. The metal combines with the enol form, which usually is the dominant one in organic solvents (e.g., K = [HTTA]en i/[HTTA]]jet = 6 in wet benzene). The kinetics of the keto -> enol reaction are not fast although it seems to be catalyzed by the presence of a reagent such as TBP or TOPO. Such reagents react with the enol form in drier solvents but cannot compete with water in wetter ones. HTTA TBP and TBP H2O species also are present in these synergistic systems. However, if extraction into only one solvent (e.g., benzene) is considered, these effects are constant and need not be considered in a simple analysis. 

The choice of reagent depends very much on the nature of the feed, but the introduction of organophosphinic acids either alone or in combination with carboxylic acids in a synergistic mixture offer great potential for commercial development. 

Hagstrom, I., Spjuth, L., Enarsson, A., Liljenzin, J.O., Skalberg, M.A., Hudson, M.J., Iveson, P.B., Madic, C., Cordier, P.Y., Hill, C., Francois, N. 1999. Synergistic solvent extraction of trivalent americium and europium by 2-bromodecanoic acid and neutral nitrogen-containing reagents. Solvent Extr. Ion Exch. 17(2) 221-242. 

The second part of the chapter deals with several kinds of asymmetric reactions catalyzed by unique heterobimetallic complexes. These reagents are lanthanoid-alkali metal hybrids which form BINOL derivative complexes (LnMB, where Ln = lanthanoid, M = alkali metal, and B = BINOL derivative). These complexes efficiently promote asymmetric aldol-type reactions as well as asymmetric hydrophosphonylations of aldehydes (catalyzed by LnLB, where L = lithium), asymmetric Michael reactions (catalyzed by LnSB, where S = sodium), and asymmetric hydrophosphonylations of imines (catalyzed by LnPB, where P = potassium) to give the corresponding desired products in up to 98% ee. Spectroscopic analysis and computer simulations of these asymmetric reactions have revealed the synergistic cooperation of the two different metals in the complexes. These complexes are believed to function as both Brpnsted bases and as Lewis acids may prove to be applicable to a variety of new asymmetric catalytic reactions.1,2... 

Paper may be deacidified to make it more permanent. Since the paper often has become brittle before it is treated, methods are needed for increasing folding endurance that may be applied in conjunction with deacidification. In this study, the effects of sorbitol and Hercules Kymene 557H on the folding endurance of three papers alkalized with magnesium carbonate are explored. A synergistic action of the reagents is apparent. 

The effect of impregnating Foldur Kraft with Kymene, with sorbitol, and with Kymene and sorbitol together is shown in Table II. The synergistic action of the two reagents on folding endurance is readily apparent. 

In 1993 Corey et al. [60] reported a new enantioselective method for synthesis of chiral cyanohydrins [61] from aldehydes and trimethylsilyl cyanide (TMSCN) by the use of a pair of synergistic chiral reagents. Reaction of cyclohexane carbaldehyde 78 and trimethylsilyl cyanide (TMSCN) 79 in the presence of 20 mol % chiral magnesium complex 80 afforded the cyanohydrin TMS ether 81 in 85 % yield with 65 % ee. This modest enantioselectivity was fiirther enhanced to 94 % ee by addition of a further 12 mol % of the bis(oxazoline) 70 (Sch. 34). 

With MAIIL,H4-fl reagents, knowing the kinetic order of the reaction would prove most helpful in discerning whether the A1—H addition occurs initially in an anti manner, or whether a syn addition is followed by an isomerization to the anti adduct. A direct anti hydroalumination would likely require the synergistic action of 2 mol of MAIR3H in the rate-determining step and thus would be second-order in complex hydride (equation 37). 

In summary, zeolites have been successfully applied as catalysts or promoters in several fundamental liquid-phase organic reactions under mild reaction conditions. The functions of the zeolites in promoting the liquid-phase reactions can be characterized by (1) synergistic effects of acidic and basic sites of the zeolites on the reactants, (2) a decrease in the activation entropy of reactions owing to preadsorption of reactants in close proximity, (3) an increase in the effective surface area of the reagent owing to high dispersion... 

The LAL reaction is specific for endotoxin with the exception of a glucose polymer from cellulose, yeast, and certain other microbial sources, known as (1 —> 3)-p-D-glucanJ This glucan activates LAL the same as endotoxin and produces a synergistic enhancement of the PPC in kinetic LAL studies. The BET allows glucan-containing products to be tested by LAL reagents that are treated to make them specific for endotoxin and avoid a false-positive result. 

A water-soluble sulfonated crown ether (see Figure 80) has been prepared and used as an ion size selection reagent. In the synergistic extraction of alkaline earth ions with 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone and trioctylphosphine oxide in cyclohexane, addition of the sulfonated crown ether shifted the extraction for the larger ions to a higher pH level, thereby improving the... 

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