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Reduction hydroxide-mediated

In work along somewhat related lines, Murakami, et al. investigated the hydroxide-mediated reduction of 8,12-diethyl-2,3,7,13,17,18-hexamethyl-cobalt(III) corrole 2.184. This involved treating 2.184 with -butyl ammonium hydroxide in the presence of ethyl vinyl ether in an aprotic solvent such as dichloromethane, benzene, or DMF. Using a similar approach, these researchers also found that iron(III) corrole 2.185 could be reduced to give the corresponding iron(II) corrole (Scheme 2.1.61). In this work, it was determined that olefins, on oxygenation with hydroxide ion, can act as the requisite electron donors for reduction. [Pg.62]

In many respects the apparently analogous reduction of nitroarenes with triruthenium dodecacarbonyl under basic phase-transfer conditions is superior to that of the iron carbonyl-mediated reductions. However, the difference in the dependence of the two processes on the concentration of the aqueous sodium hydroxide and the pressure of the carbon monoxide suggests that they may proceed by different mechanisms. Although the iron-based system is most effective under dilute alkaline conditions in the absence of carbon monoxide, the use of 5M sodium hydroxide is critical for the ruthenium-based system, which also requires an atmosphere of carbon monoxide [11]. The ruthenium-based reduction has been extended to the... [Pg.502]

Pyrite formation (FeS2) is related to biologically mediated reduction of sulfate to sulfide and of Fe3+ to Fe2+ in anoxic zones. In the case of phosphate, this can be removed through precipitation reactions with Ca2+ and Fe3+ (by formation of apatite or iron phosphate, respectively), by co-precipitation, or by formation of surface complexes with Fe or Mn oxides or hydroxides. [Pg.131]

Figure 6 shows schematically the aquatic redox cycle of iron. Under the conditions usually encountered in natural aquatic systems, the reduction of iron(III) is accompanied by dissolution and the oxidation of iron(II) by precipitation. Reductive dissolution of iron(III) hydroxides occurs primarily at the sediment-water interface under anoxic conditions in the presence of reduct-ants, such as products of the decomposition of biological material or exudates of organisms. Reductive dissolution of iron(III) hydroxides, however, can also occur in the photic zone in the presence of compounds that are metastable with respect to iron(III), that is, compounds that do not undergo redox reactions with iron(III) unless catalyzed by light. The direct biological mediation of redox processes may also influence the redox cycles of iron (Arnold et al., 1986 Price and Morel, Chapter 8, this volume). Dissolved oxygen is usually the oxidant of... [Pg.412]

Reduction of mononitroaienes mediated by P-CD has been reported using hydroxide ion as a leductant. Ordinarily the reducing ability of OH in water is very low as a result of its stabilization by hydration. Reductions by OH have only been observed in aprotic organic solvents. CD includes the reactant (nitrobenzene) and the reaction is carried out near the rim of the cavity. [Pg.109]

In vitro studies also found that aluminium hydroxide gel and magnesium oxide can cause a significant reduction in tacrolimus concentrations due to pH-mediated degradation and as a result it was suggested that the administration of antacids and tacrolimus should be separated. ... [Pg.1075]

Trifluoromethyl-purinones such as 34 and 35 have been further functionalised through conversion of the 6-oxo substituent to 6-chloro with POCI3, followed by displacement with amines [58, 59, 63, 64], 6-Chloro-2-trilluoromethyl-9-(4-methylbenzyl)purine 39 underwent partial reduction of the imidazole ring upon treatment with sodium borohydride [65] (Scheme 16). An unusual base-mediated dehydrochlorination was then observed in the presence of sodium hydroxide, to give access to the simple 6-unsubsituted 2-trifluoromethyl purine 40. [Pg.727]

The application of bases such as lithium amide (LiNH2), lithium methoxide (LiOMe) and potassium hydroxide (KOH) as additives in Sml2 mediated reactions is also known. Kamochi and Kudo (1991) reported the use of these bases in reductions of esters, carboxylic acids, anhydrides, and amides to the corresponding alcohols. These substrates are not reduced by Sml2 alone (eqs. (49)-(51)). [Pg.417]

Szucs et al found that cytochrome c formed an irreversibly adsorbed layer on the gold electrode that completely covered the electrode and which could mediate the reduction of cytochrome c in solution via electron transfer through the unfolded protein layer. Oxidation of cytochrome c in solution was not observed. They used potassium phosphate monobasic buffer (O.IA/) adjusted to pH 6.0 with potassium hydroxide. Although they investigated the behavior of cytochrome c both in the presence and in the absence of the promoter 4,4 -dipyridyl disulfide, the present discussion will focus mainly on the results obtained with bare gold electrodes. The adsorption of cytochrome c was studied by ellipsometry on bare gold electrodes at 400 mV (vs. NHE), which was approximately equivalent to the open-circuit potential of the system in the absence of... [Pg.373]

This MgBr2-mediated cycloaddition was applied to the direct synthesis of lactone 59 [29], a key intermediate for synthesis of the antibiotic clavalanine (57) (Scheme 6.19) [29a]. Thus, cyclic nitrone (5)-32 was treated with 55a in the presence of MgBra, providing ent-56a in 89% yield as the sole product. Hydrogenolysis of ent-56a in the presence of 20% palladium hydroxide caused simultaneous reductive cleavage of the N-0 bond and A -benzyl position, and lactonization to afford (35,55)-3-amino-5-hydroxy-7-lactone hydrochloride after treatment with ethanolic hydrogen chloride. Finally, the lactone hydrochloride was protected with benzyl chloro-formate to give the desired 59 in 89% yield from ent-56a. [Pg.165]


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See also in sourсe #XX -- [ Pg.62 ]




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