Discharge potential

The reduction potential of the nitrate ion is lower than the discharge potential of hydrogen, and therefore hydrogen is not liberated. The nitric acid must be free from nitrous acid, as the nitrite ion hinders complete deposition and introduces other complications. The nitrous acid may be removed (a) by boiling the nitric acid before adding it, (b) by the addition of urea to the solution ... 

On account of the fact that the electrode potential of molybdenum is more negative than the discharge potential of hydrogen, principle difficulties arise to cathodically electrodeposit molybdenum chalcogenide films from aqueous solutions. Theoretically, the deposition of pure molybdenum by electrolytic reduction of molybdates in acidic aqueous solutions is possible according to the reaction... 

In fact, the oxygen electrode is not irreversible, but the discharge potential S04 ion is so much on the high side that the OH ions are discharged preferentially, even in extremely dilute CuS04 solution. 

Figure 3.8 Amperometric detectors (a) measure the current that flows between the working electrode, usually a glassy carbon electrode, and a reference electrode, at a fixed voltage, usually close to the discharge potential for the compound. Coulometric detectors (b) are less common and are designed with a porous carbon flow cell so that all the analyte reacts in the cell, the amount of current consumed during the process being proportional to the amount of the substance.

Fig. 6.6. Discharge potential diagram (variation in current with voltage).

Glassmeyer S.T., E.T. Furlong, D.W. Kolpin, J.D. Cahill, S.D. Zaugg, S.L. Wemer, M.T. Meyer, and D.D. Kryak (2(X)5). Transport of chemical and microbial compounds from known wastewater discharges Potential for use as indicators of human fecal contamination. Environmental Science and Technology 39 5157-5169. 

Benzyl derivatives of aliphatic alcohols 73> are not reduced below the discharge potential of (C2H5)4N + in DMF [—2.9 V(SCE)]. But, they show a wave around —3.1 V(SCE) in solutions of (C4H9)4N+. Efficient reductive cleavage of benzyl methyl ether was achieved n) in THF-8% H20 with 0.25 M (C4H9)4NBF4. Under these conditions, toluene, which is the cleavage product may also be reduced and the... 

In dry acetonitiile/sodium perchlorate, however, sodium methanesulfonate and CO is obtained. A methylthiomethyl cation 159, (Eq. (220) ), is believed to be an intermediate, which is hydrolyzed to formaldehyde and methyl mercaptane. Both products are subsequently oxidized by C1207, formed by dehydration of perchloric acid, to CO and NaS03CH3 465 In spite of the fact that epe was conducted well below the discharge potential of the supporting electrolyte complications arose (Eq. (220) ), that were attributed to anodically generated C104 This observation asks for caution in the use of perchlorates as supporting electrolytes in apro-tic solvents. If possible, tetrafluoroborates or hexafluorophosphates should be used instead. 

No. Reaction type Nucleophile Discharge potential" of nucleophile versus see Mechanism6... 

Note that neat tetrahexylammonium benzoate (SSE no. 41, Table 4) has a reported anodic limit of about 0-3 V versus SCE. This value is, however, given for currents of the order of JUA and cannot be taken as the discharge potential for benzoate ion. Even traces of impurities might interfere at this current level, bearing in mind that the benzoate ion concentration is about 2 M. 

Similar results from product studies were observed with toluene as the substrate (Ross et al., 1970). Voltammetric curves from substrates with relatively high oxidation potentials were in all cases markedly displaced towards higher potentials upon addition of the toluene, a phenomenon ascribed to blocking of anode sites by adsorption of toluene. Hexamethylbenzene, with Ex j2 considerably lower than the discharge potential of nitrate ion, gives a mixture of the a-nitrate and acetate upon oxidation at 1 1 V versus see, demonstrating at least in this case that these can be products of a direct oxidation mechanism. In all cases small amounts of bibenzyl derivatives were formed, which of course necessitates the intervention of benzyl—but not nitrate—radicals at some stage of the mechanism. 

One process might outrun another one, although the order of discharge potentials would seem to indicate otherwise. 

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