Potassium ferricyanide oxidant

Schudel, P. Mayer, H. Metzger, J. Riiegg, R. Isler, O. Chemistry of vitaminE n. Structure of potassium ferricyanide oxidation product of tocopherol. Helv. Chim. Acta 1963, 46, 636-649. 

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... 

Methylation of 2,4-dimethoxy-l,8-naphthyridine was shown to take place at N-8 [to give (140)], by potassium ferricyanide oxidation to the appropriate iV-methyl naphthyridinone.152 Similarly, treatment of the monomethiodide of 1,8-naphthyridine gave the expected naphthyridin-2-one (141).56... 

N12.84% yel ndls (ale), mp 183°, subl. Prepd by nitrating the parent, heating ethyliodide with.sodium -6mitro-2-quinolonate, or by the potassium ferricyanide oxidation as with the... 

Hydroxy-[l,2,4]triazolo[4,3-fl]pyridine (91) was reluctant to react with the common hydroxylic chlorinating agents, giving at best, the 3-chloro compound in only 15% yield with pWphorus oxychloride-dimethylaniline. Methylation of (91) produced 2-methyl-[l,2,4]triazolo[4,3-n]pyrid-3-one (92) whereas methylation of the 3-thiol (93) resulted in methyl [l,2,4]triazolo[4,3-a]pyrid-3-yl sulfide (94), a molecule also resistant to nucleophilic substitution (66JOC265). Potassium ferricyanide oxidation of (93) resulted in the corresponding disulfide. 

Thiamine hydrochloride is stable in acid but unstable in aqueous solutions with a pH above S. Under lhe.se conditions. it undergoes decomposition and inactivation. Exposure of thiamine to the atmosphere or to oxidizing reagents such as hydrogen peroxide, permanganate, or alkaline potassium ferricyanide oxidizes it readily to ihiochromc, shown below. Thiochromc exhibits a vivid blue fluorescence hence, this reaction is the basis for the quantitative fluoro-metric assay of thiamine in the USP. 

In recent work Kende and his coworkers have explored intramolecular oxidative coupling between phenolate and enolate, rather than between two phenolates. This proved a viable process for certain carbonyl enolates, and for nitro-stabilized anions, llius potassium ferricyanide oxidations of the indandione... 

Alkaline potassium ferricyanide oxidation of A/ -substituted pyridinium salts often is amethod of choice for the preparation of A -alkyl-2-pyridones. For example,... 

Figure 4. EPR (top) and UV/Vis (bottom) spectra of synthetic Hb hybrids. Reductive nitro-sylation [24] of met-Hb (prepared from Hb A<, by potassium ferricyanide oxidation foilowed by G-25 chromatography) with one equivalent of NO give Hb[(a-Fe(III))2(P-Fe(II)NO)2] (left), while limited air oxidation of Hb(NO)4 furnishes Hb[(a-Fe(II)NO)2(P-Fe(III))2] (right). SoUd lines are the experimental spectra, the dotted line on the UVA is spectra represents a simulation constructed from equal mixtures of heme-Fe(lll)and heme-Fe(II)NO standard Hb spectra. EPR spectra were obtained at X-band (9.3 GHz), with sanities at 76 K, and detected with a field modulation anqilitude of 5 G and frequency of 100 kHz.

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