Process two-electron

Figure 4 Schematic electron energy level diagram (a) of a core-level photoelectron ejection process (one electron process) (b) core-level photoelectron ejection process with shake-up (two- electron process) (c) schematic XPS spectrum from (a) plus (b) (d) Cu 2pa/2 XPS spectrum for Cu in CU2O and Cu in CuO. The latter shows strong shake-up features.

Example 2-1 The reversible oxidation of dopamine (DA) is a two-electron process. A cyclic voltammetric anodic peak current of 2.2 pA is observed for a... 

Thus, under suitable experimental conditions, all aromatic sulphones are cleaved, in most cases by a two-electron process summarized by equations 1 and 2. Such reactions have been established1-5 by means of coulometric titration, isolation of cleavage residues ArH and RH and chemical identification of the anion ArS02- (e.g. by treatment of the... 

The experimental results described in this work64 concerning the sulfoxide and the sulfones can also be explained by a two-electron process in agreement with electrochemical evidence and photosensitized reactions (see the previous section), using the successive reactions1 ... 

Before considering the role of the electrode material in detail, there is one further factor which should be pointed out. The product of an electrode process may be dependent on the timescale of the contact between the electroactive species and the electrode surface, particularly when a chemical reaction is sandwiched between two electron transfers in the overall process. This was first realized when it was found that ir E curves and reaction products at a dropping mercury electrode were not always the same as those at a mercury pool electrode (Zuman, 1967a). For example, the reduction of p-diacetylbenzene at a mercury pool was found to be a four-electron process, giving rise to the dialcohol, while at a dropping mercury electrode the product was formed by a two-electron process where only one keto group was reduced (Kargin et al., 1966). These facts were interpreted in terms of the mechanism... 

Susac et al. [33] showed that the cobalt-selenium (Co-Se) system prepared by sputtering and chemical methods was catalytically active toward the ORR in an acidic medium. Lee et al. [34] synthesized ternary non-noble selenides based on W and Co by the reaction of the metal carbonyls and elemental Se in xylenes. These W-Co-Se systems showed catalytic activity toward ORR in acidic media, albeit lower than with Pt/C and seemingly proceeding as a two-electron process. It was pointed out that non-noble metals too can serve as active sites for catalysis, in fact generating sufficient activity to be comparable to that of a noble metal, provided that electronic effects have been induced by the chalcogen modification. 

Methyl 2-furoate was dimethoxylated using methanol in sulfuric acid to give methyl-2,5-dihydro-2,5dimethoxy-2-furan carboxylate [70]. The reaction mechanism at the electrodes is not completely known. However, the anodic reaction is said to be the oxidation of methanol. A two-electron process is assumed and hydrogen production is observed at the cathode. 

Aromatic nitro and nitroso compounds are easily reduced at carbon and mercury electrodes. Other nitro compounds such as nitrate esters, nitramines, and nitrosamines are also typically easily reduced. The complete reduction of a nitro compound consists of three two-electron steps (nitro-nitroso-hydroxylamine-amine). Since most organic oxidations are only two-electron processes, higher sensitivity is typically found for nitro compounds. Several LCEC based determination of nitro compounds have been reported... 

The anodic reaction (taking place in the illuminated cell compartment) is a two-electron process regenerating the initial form of Thi+ ... 

The binuclear Ir complex (93) is produced from the direct coupling reaction of the Ir-bound 5-chloro-phen ligand as shown in reaction Scheme 12.153 The nonplanar structure of the bridging ligand results in the electronic isolation of the two Ir centers. Hence both metal centers and ligands are oxidized and reduced, respectively, in two-electron processes. 

On the basis of the above observations, Angerstein-Kozlowska and colleagues (1973) reasoned thus even at peak Oa3, less than 1 electron per Pt atom has passed, therefore, it is highly unlikely that the oxidation of the surface proceeds via a single two-electron process, i.e. ... 

On both Hg and Au, CO was a product, as shown by GC measurements, with formate also a product, as detected by quantitative analysis. The formation of CO from a process giving I e per molecule of C02 is, at first sight, somewhat contradictory since the formation of CO from C02 is nominally a two-electron process. This led the authors to postulate that the mechanism involved the coupling of two of the initially produced COj radicals leading to disproportionation ... 

The UV/Vis, Mossbauer, EXAFS, and EPR spectroscopic data suggest a rather complicated picture regarding the speciation of oxidized TAML species derived from 1 and various oxidants in aqueous solution (Scheme 5). Peroxides ROOH have the capacity to function as two-electron oxidants and usually do. In cases where prior coordination occurs, they can oxidize metal ions via one-electron processes where the 0-0 bond is cleaved homo-lytically or two-electron processes where it is cleaved hetero-lytically. The two-electron oxidation of 1 presumably would give the iron-oxo intermediate 6, two electrons oxidized above the iron(III) state (see below). Before 6 was actually isolated, there... 

For practical applications it is important to minimize the production of the intermediate peroxide, and to ensure that the reaction goes all the way to water. Sometimes this can be ensured by the addition of a suitable catalyst. A case in point is oxygen reduction on gold from alkaline solutions. At low and intermediate overpotentials the reaction produces only peroxide in a two-electron process at high overpotentials the peroxide is reduced further to water. The addition of a small amount of Tl+ ions to the solution catalyzes the reaction at low overpotentials, and makes it proceed to water. Thallium forms a upd layer at these potentials it seems that a surface only partially covered with T1 is a good catalyst, but the details are not understood [3]. 

Although some other two-electron processes may exist and may be found in the future, the 15 Patterns shown in Scheme 1.3 should cover most of the known two-electron processes. The following additional discussions of these patterns might be useful in dealing with them. 

Olivero et aL have found a new electrochemical domino process.1941 In an dectrochemical overall two-electron-process in an one-compartment cell... 

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