Ferricyanide as oxidant

Mechanistic studies of the chemical oxidation of aliphatic amines have been reviewed extensively by Chow et al. [22]. Many studies of the mechanism of oxidation of amines have been performed with chlorine dioxide or ferricyanide as oxidants, because they have absorption bands with maxima at 357 and 420 nm, respectively. Changes in the absorbance at these wavelengths for the respective oxidants can be conveniently used to follow the kinetics of the reactions. On the basis of these studies, the electron-transfer mechanism shown in Scheme 1 has been proposed for amine oxidation. 

Mercuryil) perchlorate also has been used as a reductant, in conjunction with alkaline ferricyanide as oxidant. Reducing agents such as Cr(II), hydrogen peroxide, hydrazine, and As(III) are treated with an excess of standard ferricyanide and back-titrated. Merrer and Stock found 0.01 M solutions of Hg(I) perchlorate to change concentration with time. 

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... 

Luminol amidine 132, synthesized from luminol and the Vilsmeier reagent from DMF and thionyl chloride, has been proposed as a suitable luminol derivative for analytical purposes because, unlike luminol, it can be easily purified by recrystallization from water. 132 exhibits a chemiluminescence quantum yield of about 20% of luminol in ferricyanide-catalyzed oxidation by aqueous alkaline hydrogen peroxide Amax of the emission is 452 nm 196>. 

For analysis in solutions, the most frequently used CL reaction is alkaline oxidation of luminol and lucigenin in the presence of hydrogen peroxide as oxidant, although sodium hypochlorite, sodium perborate, or potassium ferricyanide may also be used. CL reactions involving alkaline oxidation have been used to indicate acid-base, precipitation, redox, or complexometric titration endpoints either by the appearance or the quenching of CL when an excess of titrant is present [114, 134], An example of these mechanisms is shown in Figure 14. 

Here A and B are non-luminescence molecules. The C is the excited state of the product C. Often these reactions involve oxidation reactions and the presence of a catalyst. Both chemical and biochemical reactions could generate the photon. The intensity of the photons are collected through optical fibers and measured with a photon detector. The most successful chemiluminescence sensor for the detection of the hydrogen peroxide [13] is based on luminol using ferricyanide as catalyst... 

The preparation of aryllithium reagents can also be performed by using t-butyllithium in a halogen-metal exchange, and aqueous potassium ferricyanide as an oxidant. 

Fig. 14. Schematic representation of light-driven (2e + 2H+) symport across a membrane via the quinone carrier molecule vitamin Kj and its hydroquinone form proflavine (PF)-sen-sitized photoreduction of methyl-viologen MV2+ in the RED phase, yields the reducing species MV+, with simultaneous oxidative decomposition of EDTA used as electron donor the OX phase contains ferricyanide as electron acceptor [6.49].

Reference system complex metal cyanides, 20 ml. of a 0.03M aqueous solution and 200 ml. 15W S0rensen buffer containing organic solvents (for detailed description see Experimental), apparent pH 7.45. Electrodes combined platinum electrode with Ag/AgCl in saturated KC1 as reference electrode. Reaction temperature 20°C. Abbreviations Reference systems named as oxidants—Fe, potassium ferricyanide Mo, potassium molybdicyanide. Mv.—millivolts. 

The original procedure has been modified by the use of a slow addition of the alkene to afford the diol in higher optical purity, and ironically this modification results in a faster reaction. This behavior can be rationalized by consideration of two catalytic cycles operating for the alkene (Scheme 9.20) the use of low alkene concentrations effectively removes the second, low enantio-selective cycle.145151 The use of potassium ferricyanide in place of A-methylmorpholine-iV-oxide (NMMO) as oxidant also improves the level of asymmetric induction.152153... 

Nearly any primary alcohol serves as a substrate with the exception of methanol and ethanol. Ferricyanide (17, 18), porphyrexide (18), and hexachloroiridate(IV) (18) can replace oxygen as oxidant. Hexachloro-iridate(IV) is consumed to the exclusion of oxygen in aerobic mixtures. When hexachloroiridate(IV) and H202 serve as oxidant and reductant respectively, the normal reaction, vis-a-vis H202, is reversed, and oxygen is produced (18). 

Later 2-methyl-6-nitrobenzothiazole was obtained by electrochemical oxidation of 4-nitrothioacetanylide [568], Interestingly, there is no cyclization under the influence of potassium ferricyanide when arylthioureas are used. In this case other cyclizating agents have to be used as oxidizers. Bromine-induced oxidation of nitroarylthiourea with the formation of the corresponding 2-aminobenzothiazole nitroderivatives (Hugershoff s method) is used for preparative purposes [182, 569-574], Sometimes sulfur monochloride is used as an oxidizer in place of bromine (Scheme 2.98) [575, 576],... 

Scheme 5.13 Catalytic cycle for AD-reaction with potassium ferricyanide as co-oxidant...

The physiological pathway of electron transfer in flavocytochrome is from bound lactate to FMN, then FMN to 52-heme, and finally 52-heme to cytochrome c (Fig. 9) (2,11, 80,102). The first step, oxidation of L-lactate to pyruvate with concomitant electron transfer to FMN, is the slowest step in the enzyme turnover (103). With the enzyme from S. cerevisiae, a steady-state kinetic isotope effect (with ferricyanide as electron acceptor) of around 5 was obtained for the oxidation of dl-lactate deuterated at the C position, consistent with the major ratedetermining step being cleavage of the C -H bond (103). Flavocytochrome 52 reduction by [2- H]lactate measured by stopped-flow spectrophotometry resulted in isotope effects of 8 and 6 for flavin and heme reduction, respectively, indicating that C -H bond cleavage is not totally rate limiting (104). 

Kinetic analysis of TD-62 under steady-state conditions with ferricyanide as electron acceptor showed that kcat and Km values for L-lactate (165 sec and 0.96 mM, at 25°C, 10 mM Tris-HCl, pH 7.5, / = 0.10 M NaCl) were not dramatically different from the values determined for wild-type enzyme (200 sec and 0.49 mM, conditions as above) 144). However, the behavior of TD-62 under assay conditions was unusual in that the rate of lactate oxidation decreased long before either L-lactate or ferricyanide became depleted. The decrease in reaction rate occurred as a biphasic process, leading eventually to complete loss of activity. This deactivation of TD-62 was only observed under turnover conditions. Deactivation was independent of ferricyanide and was also observed when cytochrome c was used as electron acceptor (150). 

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