Potassium ferricyanide catalyst

Mono-, di-, and trisubstituted olefins undergo osmium-catalyzed enantioselective dihydroxylation in the presence of the (R)-proline-substituted hydroquinidine 3.9 to give diols in 67-95% yields and in 78-99% ee.75 Using potassium osmate(VI) as the catalyst and potassium carbonate as the base in a tm-butanol/water mixture as the solvent, olefins are dihydroxylated stereo- and enantioselectively in the presence of 3.9 and potassium ferricyanide with sodium chlorite as the stoichiometric oxidant the yields and enantiomeric excesses of the... 

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

Some experimentation afforded improvements to the process. For example, in the case of the AD reaction, both the osmium and chiral concentrations could be reduced to a level of 0.05 mol % and 0.25 mol %, respectively, or one-fourth the levels in the commercial AD-mix formulation, without compromising the yield and enantiomeric excess of the etude product. The volume of liquid was also reduced to one-fourth of the quantities reported (1.5 L of water and 1 L tert-butyl alcohol per mole of substrate versus 5 L of water d 5 L of tert-butyl alcohol per mole of substrate). Under these conditions the reaction mixture is a slurry, but the potassium ferricyanide dissolves as it reacts. Reducing the catalyst concentration had the effect of doubling the reaction time from 1 day to 2 days. Interestingly, a study on the use of reduced amounts of osmium in the AD reaction of 1-phenyl-1-cyclohexene concluded that reducing the quantity of osmium by half (to 0.1 mol %), doubled the reaction time without affecting the yield, but that further reductions h osmium content made the reaction too sluggish to be useful. ... 

The use of zinc sulfate to catalyze the potassium ferricyanide oxidation procedure251 is worthy of comment. It is possible that other metals would also catalyze this oxidation, but their presence in the system would have a deleterious effect on thfe fluorescence of the final product, while Zn++ ions have relatively little effect. For instance, Cu++ ions would be expected to catalyze the oxidation stage, but they would also have a strong quenching effect on the fluorescence of the final products.144 Some of the Zn++ ions will also presumably be removed from the solution as insoluble zinc ferro-cyanide. Anton and Sayre have recently questioned the value of zinc sulfate as a catalyst at low pH.252... 

Potassium ferricyanide, 255 of silyl enol ethers and lithium enolates Iodosylbenzene, 151 Miscellaneous methods Palladium catalysts, 230 Tetrakis(trifluoroacetate)ruthenium,... 

Pour a small pile (approximately the size of a dime) of potassium ferricyanide crystals into a small white plastic container. Add about 90.0ml of water, then a splash of plain hypo. The splash will vary based on desired contrast of the mixture. The hypo acts as a catalyst, but ultimately neutralizes the bleach. A solution strong in ferricyanide and low in hypo is fairly contrasty. One lower in ferricyanide and higher in hypo is lower in contrast and slower acting. With experience, you will be able to judge bleach strength by its color saturation. 

In the studies of the synthesis of the ansamycin antibiotic rifamycin S (13S), Corey and Clark [76] found numerous attempts to effect the lactam closure of the linear precursor 132 to 134 uniformly unsuccessful under a variety of experimental conditions, e.g. via activated ester with imidazole and mixed benzoic anhydride. The crux of the problem was associated with the quinone system which so deactivates the amino group to prevent its attachment to mildly activated carboxylic derivatives. Cyclization was achieved after conversion of the quinone system to the hydroquinone system. Thus, as shown in Scheme 45, treatment of 132 with 10 equiv of isobutyl chloroformate and 1 eqtuv of triethylamine at 23 °C produced the corresponding mixed carbonic anhydride in 95% yield. The quinone C=C bond was reduced by hydrogenation with Lindlar catalyst at low temperature. A cold solution of the hydroquinone was added over 2 h to THF at 50 °C and stirred for an additional 12 h at the same temperature. Oxidation with aqueous potassium ferricyanide afforded the cyclic product 134 in 80% yield. Kishi and coworkers [73] gained a similar result by using mixed ethyl carbonic anhydride. 

Gas chromatographic methods measure the carbon monoxide content of blood. Y/hen blood is treated with potassium ferricyanide, carboxyhemoglobin is converted to methemoglobin, and the carbon monoxide is released into the gas phase. Measurement of the released carbon monoxide may be performed by GC using a molecular sieve column and a thermal conductivity detector. A lower detection limit is achieved by incorporating a reducing catalyst (e.g., nickel) between the GC column and the detector to convert... 

Acrylamide grouts at ambient temperatures are catalyzed with a two-component redox system. One part, the initiator or catalyst, can be a peroxide or a persalt. Ammonium persulfate (AP), a powder, is most commonly used. The second part, the accelerator or activator, is an organic such as triethanolamine, (TEA), nitrilotrispropionamide (NTP), or dimethylaminiopropionitrile (DMAPN). All three have disadvantages. DMAPN, a liquid, is best from a control point of view but is considered a health hazard. NTP, a powder, has limited solubility in water, particularly at low temperatures. TEA, a liquid, is somewhat metal-sensitive. At the present time virtually all U.S. applications use TEA. There are also materials which act as inhibitors and can be used reliably to control gel time. Potassium ferricyanide, KFe, is most often used. 

Platinum catalyst for reductions, 15, 89 Potassium acetate, 13, 36 Potassium bichromate, 12, 64 Potassium ferricyanide, 16, 41... 

---