Oxidation with ferricyanide

Besides what has been mentioned above, a number of oxidations can be performed in aqueous phase in the presence of a phase transfer catalyst (see Chapter 8). 

Like oxidation, reduction of organic molecules has played an important role in organic synthesis. A number of reducing agents with different substrates have been described. 

In the present unit, some examples of a few novel reduction performed in aqueous medium are described. Enzymic reduction have also been known to occur in water. However, this subject will be discussed in a separate section. Some important reductions in aqueous media are given as follows  

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A second unusual EPR spectrum was observed in the oxidized (as-isolated) protein (Fig. 3). This spectrum, which was assigned to an S = z system, was not reminiscent of any Fe-S cluster. Indeed, with g-values of 1.968, 1.953, and 1.903, it looked more like a molybdenum or tungsten spectrum. However, chemical analysis ruled out the possibility that this EPR spectrum arose from Mo or W, and the spectrum was assigned to an Fe-S center instead. The spin concentration, however, was sub stoichiometric and sample-dependent. Furthermore, when the as-isolated protein was oxidized with ferricyanide, it became EPR silent. This, together with the iron determination and the fingerprint of the reduced protein, led Hagen and colleagues to the... 

Various nitrosoarenes have been utilized as benzofurazan precursors including o-azido derivatives generated from the o-chloro analogues <66JCS(B)1004>, and 1-amino-2-nitrosoarenes which can be oxidized with ferricyanide or hypochlorite. Treatment of o-nitrosophenols with hydroxylamine also affords the furazan, presumably via an oximation-dehydration pathway involving the tautomeric o-quinone monooxime. Other related approaches involve the reduction of o-dinitroarenes with borohydride, and the thermolysis of o-nitroanilines and o-nitroacetanilides. 

Potentiometric reductive titration, using both fresh thylakoids and PS II particles previously oxidized with ferricyanide, has revealed that the LP couple exhibits a constant midpoint redox potential ( o- +° 12 v ) above pH 7.6, but becomes pH-dependent below this pH, with a slope of about -60 mV pH pH unit, whereas the HP couple is pH-independent in the pH range between 6.5 an 8.5 ( o-+0 36 V) in general, cytochrome b-559 exhibits potential values about 40 mV lower in thylakoids than in PS II particles. After mild heating of the fresh preparations or treatment with the detergent Triton X-100, the HP couple is converted into the LP couple, which preserves its characteristic pH-dependence. In contrast, in the presence of the uncoupler CCCP, the HP couple is also converted into the LP couple, but the pH-dependence proper to the latter is now lost. 

Beta dinitrotoluene upon oxidation with ferricyanide forms the corresponding dinitrobenzoic acid. 

Historically, assessment of thiamine status was by animal bioassay (the correction of bradycardia in thiamine-deficient rats) and later by microbiological assays using the fungus Phycomyces hlakesleeanus, yeast fermentation, or bacteria of the Staphylococcus, Streptococcus, or Lactobacillus species. Some bacterial microbiological assays are still in use in the food industry. Early chemical methods were often based upon the production of a fluorophore, thiochrome, when thiamine is oxidized with ferricyanide in alkaline solution, a property that is used in some modern chromatographic methods. 

Figure 3. Fe(III) EPR signals in A. nidulans obtained after the oxidation with ferricyanide in the presence of acceptor-side inhibitors. (A), control (B), with 1.1 mM DCMQ (C), with 28 mM o-phenathroline.

Jansen adapted this reaction for the querntitative determination of thiamine . The oxidation with ferricyanide in alkaline medium is carried out on an extract of the vitamin treated as mentioned above. The thiochrome formed is extracted into isobutanol and the fluorescence of the extract measured. The fluorescent products formed from the thiamine phosphates are only shghtly soluble in isobutanol. 

An important mode of oxidation for -phenylenediamines is the formation of ben2oquinonediimines, easily obtained by oxidation with silver oxide in ether solution (17). DHmines undergo 1,4 additions with amines to generate tri- and tetraamines which readily oxidi2e in air to highly conjugated, colored products. An example of this is the formation of Bandrowski s base [20048-27-5] when -phenylenediamine is oxidi2ed with potassium ferricyanide (18). 

Fig. 3. Cation-exchange chromatography of protein standards. Column poly(aspartic acid) Vydac (10 pm), 20 x 0.46 cm. Sample 25 pi containing 12.5 pg of ovalbumin and 25 pg each of the other proteins in the weak buffer. Flow rate 1 ml/min. Weak buffer 0.05 mol/1 potassium phosphate, pH 6.0. Strong buffer same +0.6 mol/1 sodium chloride Elution 80-min linear gradient, 0-100% strong buffer. Peaks a = ovalbumin, b = bacitracin, c = myoglobin, d = chymotrypsinogen A, e = cytochrom C (reduced), / = ribonuclease A, g = cytochrome C (oxidised), h = lysozyme. The cytochrome C peaks were identified by oxidation with potassium ferricyanide and reduction with sodium dithionite [47]...

A few data exist on the oxidation by ferricyanide. This is simple second-order (in oxidant and neutral hydrazine), and leads to quantitative production of nitrogen in accordance with scheme (71)-(74) with A 4 k and A i. No scrambling occurs during oxidation of N-labelled N2H4 indicating that all N2 is formed via di-imine" Di-imine so prepared is capable of hydrogenating added unsaturated compounds, for example, phenylpropiolic acid gives m-cinnamic acid" " . 

Mercaptopropionic acid (HRSH) has been oxidised with ferricyanide in aqueous solution to give 3,3 -dithiodipropionic acid in 95 % yield. Whilst individual runs showed second-order disappearance of oxidant, the magnitude of 2 varied with increasing thiol, oxidant and ferrocyanide concentrations , viz. 

Ferricyanide has been employed as an electron acceptor for lactate in place of NAD Alternatively, diaphorase can be used in conjunction with ferricyanide Bindschedler s Green ferricenium or dichlorophenylindophenol to catalyze the oxidation of NADH while providing a more easily monitored species than NADH itself. 

The discovery by Knaff and Amon(32) of a light-induced photooxidation at — 189°C requiring short-wavelength light has provided information as to a possible primary electron donor for Sn. The photooxidized substance has been identified as a form of cytochrome b absorbing at 559 nm (cytochrome 559)- Pretreatment of the spinach chloroplasts with ferricyanide to oxidize... 

In the case of dioximes bearing different substituents (R Ri) the furoxan isomer obtained can depend on the configuration of the starting dioxime. The classic example is the oxidation of p-methoxybenzil dioxime with ferricyanide (Scheme 6.5) this reaction affords the 4-phenyl furoxan isomer 18 in a regiospecific manner if the dioxime amphi-form 19 is used, the 3-phenyl isomer 20 is produced if the amphi-... 

Oxidation with ammonium persulfate and dilute caustic soda gives bismuth tetroxide, Bi204. The same product can be obtained by using other oxidizing agents such as potassium ferricyanide and concentrated caustic potash solution. 

Oxidation of acetyl- and acetylnitro-substituted thienothiophenes 1 and 2 with ferricyanide or hypoiodite to the corresponding acids was used primarily to confirm the site of electrophilic substitution at position 2 in the thienothiophenes. " Permanganate degrades the thieno[3,2-A]-thiophene (2) ring system, while potassium hypobromite produced bromo derivatives of thieno[2,3-6]thiophene-2-carboxylic acid. ... 

The C-hydroxylation of benzoquinolizinium ions is easier and, although the position of the attack on benzo[a]quinolizinium (2) salts is not known, it has been demonstrated (67JOC733) that hydroxylation of the acridizinium (benzo[6]quinolizinium, 3) ion must occur at position 6 (Scheme 8). It was not possible to obtain a pure sample of the pseudobase (17) or the 2-(2-formylbenzyl)pyridine (18) in equilibrium with it, but oxidation of the mixture with ferricyanide afforded a small amount of benzo[Z>]quinolizinone (19) (62CI(L)1292), while reaction with hydroxylamine afforded a good yield of 2-(2.-pyridyl-methyl)benzaldoxime (20) (67JOC733). 

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