Ferrocyanide oxidation

FIG. 8 SECM steady-state current-distance approach curves with substrates of rutile (001) (A, A), and albite (010) ( , ). In each case the filled symbols are data for H+ reduction and open symbols are tip-substrate distance calibration data for ferrocyanide oxidation. The solid lines show the negative feedback behavior for an inert substrate and an electrode geometry characterized by RG = 10 (rutile experiments) and RG = 20 (albite experiments). 

FIG. 25 SECM experimental approach curves showing the variation of the initially attained steady-state current for ferrocyanide oxidation at UMEs with a = (a, ) 12.5 /r,m, (b, ) 5 fim, and (c, ) 2.5 /rm, with distance between the tip and the potassium ferrocyanide trihydrate (010) surface. The data were derived from chronoamperometric measurements. For comparison, the theoretical behavior for a diffusion-controlled dissolution process (.) is also shown along with the best fits to the experimental... 

Garcia et al. [77,78] reported an electron transfer percolation threshold in highly resistive oil-continuous microemulsions. The Faradaic electron transfer is modulated by the amount of cosurfactant present in AOT-toluene-water microemulsions. Below a certain threshold concentration of the cosurfactant, the electron transfer between electroactive solutes in the water droplets and ultramicroelectrode is retarded or blocked. Electron transfer becomes facilitated, and a sharp increase in Faradaic current is observed above the threshold concentration. This effect was demonstrated for ruthenium hexamine reduction [77,78], ferrocyanide oxidation [77,78], acrylamide oxidation [77], and allQ lamide oxidation [77,79] with acrylamide, alkylamides, and acetonitrile as cosurfactants in AOT microemulsions. NMR results [80] suggest that there is an interfacial packing transition of the surfactant (AOT) at about the same cosurfactant concentration as the threshold transition observed electrochemically. 

Another approach using nonlinear frequency respruise analysis with the help of the Volterra series expansirui and generalized Fourier transform was also proposed and applied to the study of methanol or ferrocyanide oxidation [666-668]. 

Similar threshold phenomena have been reported for the reduction of persulfate in reverse microemulsion polymerization of acrylamide [12,13], for ferrocyanide oxidation in similar microemulsions utilizing acetonitrile as cosurfactant [29], and for the autocatalytic oxidation of acrylamide and a variety of primary alkylamides where the respective amides served as cosurfactant [31]. 

Hence the second wave should exhibit linear Koutecky-Levich behavior. Equation 88 appears to be quite complex, but it can be simplified in the limit of very large K, which is a valid approximation for the ferrocyanide oxidation at the ruthenium-containing homopolymer currently being considered (where K = 10 ). We note that as K becomes very large then... 

Formation of another reaction product - ferrocyanide - was recorded with the use of the dropping electrode [66] (Fig. 24). An anodic wave due to ferrocyanide oxidation arose after illumination under the conditions indicated and had a half-wave potential of +0.2 V with respect to the saturated calomel electrode. Comparison of the limiting currents of ferricyanide specially introduced into this system with those of the products resulting from Eq. (20) shows that the concentration of the latter is approximately... 

Example 16.3-2 The rate of ferrocyanide oxidation We are studying electrochemical kinetics using a flat platinum electrode 0.3 cm long immersed in a flowing aqueous solution. In one series of experiments, the solution is 1-M KCl containing traces of potassium ferrocyanide. The ferrocyanide is reduced by means of the reaction... 

Hexa.cya.no Complexes. Ferrocyanide [13408-63 ] (hexakiscyanoferrate-(4—)), (Fe(CN) ) , is formed by reaction of iron(II) salts with excess aqueous cyanide. The reaction results in the release of 360 kJ/mol (86 kcal/mol) of heat. The thermodynamic stabiUty of the anion accounts for the success of the original method of synthesis, fusing nitrogenous animal residues (blood, horn, hides, etc) with iron and potassium carbonate. Chemical or electrolytic oxidation of the complex ion affords ferricyanide [13408-62-3] (hexakiscyanoferrate(3—)), [Fe(CN)g] , which has a formation constant that is larger by a factor of 10. However, hexakiscyanoferrate(3—) caimot be prepared by direct reaction of iron(III) and cyanide because significant amounts of iron(III) hydroxide also form. Hexacyanoferrate(4—) is quite inert and is nontoxic. In contrast, hexacyanoferrate(3—) is toxic because it is more labile and cyanide dissociates readily. Both complexes Hberate HCN upon addition of acids. 

Ferric ammonium ferrocyanide—The blue pigment obtained by oxidising under acidic conditions with sodium dichromate the acid-digested precipitate resulting from mixing solutions of ferrous sulfate and sodium ferrocyanide ia the presence of ammonium sulfate. The oxidized product is filtered, washed, and dried. The pigment consists principally of ferric ammonium ferrocyanide with small amounts of ferric ferrocyanide and ferric sodium ferrocyanide. 

Ideally, 20.2 pounds of the ferrocyanide can be converted to 11.7 pounds of ferricyanide by one pound of ozone. Indeed, ozone oxidation efficiency is nearly 100 percent for ferrocyanide concentrations above 1.0 g/1. 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Ferrifeiro-cyanid, n. ferric ferrocyanide (Prussian blue), -jodid, n. ferroeoferric iodide, -oxyd, n. ferroeoferric oxide, iron(II,III) oxide. 

DinitroT -Naphthol (4,8-Dinitro-1 -oxy-naphthalene). Yellow needles from 25% alc/w mp, turns black at 200° melts at 235° (decompn). Sol in ale, AcOH cold Na carbonate soln. Prepn from 8-nitro-naphthochinon-(l,4)-oxime-(4) by oxidation with alkaline K ferrocyanide Ref Beil 6, 619 i... 

Ferrocyanides stability, 6, 830 Ferrocytochrome c oxidation, 6, 621 Ferroin, 4,1203 redox indicator. 1,558 Ferrokinetics... 

Hydroxyl radicals. The acid ionization constant of the short-lived HO transient is difficult to determine by conventional methods but an estimate can be made because HO, but not its conjugate base, O -, oxidizes ferrocyanide ions HO + Fe(CN) — OH- + Fe(CN)g . Use the following kinetic data26 for the apparent second-order rate constant as a function of pH to estimate Ka for the acid dissociation equilibrium HO + H20 =... 

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. 

The aqueous ferricyanide oxidation of 2-mercaptoethanol to the disulphide is also complex kinetically" . In the pH range used (l.S. l) no complication from ionisation of the thiol is expected. Individual decays of oxidant concentrations are initially second-order but eventually become almost zero-order. For both second-and zero-order paths the rate depends on the first power of the thiol concentration and the former path is retarded by increasing the acidity, an approximately inverse relation existing above pH 3.2. Addition of ferrocyanide transforms the kinetics the rapid, second-order path is inhibited and the zero-order path is accelerated until, at 10 M ferrocyanide, the whole of the disappearance of oxidant is zero-order. Addition of Pb(C104)2, which removes product ferrocyanide, greatly enhances the oxidation rate and the consumption of oxidant becomes rs/-order. Two routes are considered to co-exist (taking due account of the acidity of ferrocyanic acid), viz. 

The reduction of iodine by ferrocyanide is simple second-order with Aij (25 °C) = (1.3 + 0.3)x 10 l.mole sec This is the reverse of the oxidation of iodide by ferricyanide (p. 409), but the ratio k(forward)/k(back) does not agree well with the equilibrium constant determined potentiometrically. Addition of 1 strongly retards the reduction and 13 was discounted as a reactant, the mechanism suggested being... 

Other solutions to dealing with interferences in the detection of H O have included the use of a copperfll) diethyldithiocarbamate precolumn to oxidize the sample before it reaches the immobilized enzyme, as well as the use of a palladium/gold sputtered electrode which catalyzes the oxidation of hydrogen peroxide In addition, peroxidase has been used to catalyze the reaction between hydrogen peroxide and iodide ferrocyanide and organo-fluorine compounds Am-... 

---