Oxidation of cations

Reactions with Parting of Radicals. The one-electron oxidation of cationic dyes yields a corresponding radical dication. The stabihty of the radicals depends on the molecular stmcture and concentration of the radical particles. They are susceptible to radical—radical dimerization at unsubstituted, even-membered methine carbon atoms (77) (Fig. 6). 

Oxidation of complex sulphide ores — competitive oxidation of cations... 

The broad oxidation processes at E > 0 mV are partly due to Si oxidation, gold oxidation and oxidation of cation reduction products. 

Often, with precipitation reactions the starting materials are limited to whatever salts are soluble in the solvent of choice. For water systems this is often limited to metal salts of halides, nitrates, and some sulfates and phosphates. Halides, in particular chlorides, have a pronounced effect on precipitation reactions. Chlorine is able to form bridged complexes much like the hydroxides or oxides of the desired compounds. In addition, acidic environments make possible the oxidation of chloride to chlorine gas, which can further complicate the synthesis. Sulfates and phosphates are typically easier to work with since they do not have the complicated redox behavior of the halides, but they typically have reduced solubilities. Nitrates, although they do not have the solubility concerns of sulfates and phosphates, do have redox complications, which typically result in oxidation of cations. So, the anion, which is expected to act solely as a spectator, in many cases is actually acting as a catalyst. 

K2NiF6 in aHF is also useful for the fluorination of organic substrates. Its ability to fluorinate is probably enhanced by the negative charge carried by the NiF oxidizer in solution especially so in the oxidation of cationic substrates [61]. 

Yellowing This problem arises especially with undyed fabrics. It can be caused by the oxidation of cationic softeners or amino-modified silicones or by the ionogen attraction of cationic softeners and anionic fluorescent brighteners (extinguishing the fluorescence by salt formation). Dispersing agents and product selection are then helpful. 

Non-stoichiometric oxides may contain either an excess of metal (e.g. zinc oxide, Zni+jO) or a deficiency of metal (e.g. nickel oxide, Ni,.jO). Some metal oxides (e.g. titanium oxide) may be prepared as either excess-metal or metal-deficit oxides. Excess metal is incorporated in the structure as interstitial cations together with the electrons removed through ionization. In metal-deficit or excess-oxygen oxides, excess oxygen is incorporated in the structure by formation of cation vacancies and positive holes, which may be achieved by oxidation of cations, e.g. 

Appearance of the current carriers as electron holes is connected to the oxidation of cations, that is, with their loss of electrons Me —> + , where is the hole. 

Quite a different situation takes place for the reduction of anions, or for the oxidation of cations. Then the diffuse-layer multiplier, Kfi, varies in the opposite direction compared to the Tafel term. For sufficiently dilute solutions, the former factor dominates and the cathodic current diminishes at the negative shift of the electrode potential in the vicinity of the p.z.c. At higher electrode charges (positive or negative) the variation of the diffuse-layer potential becomes very slow (logarithmic function of the electrode charge, Eq. (17)) compared with the overall... 

Figure 5.30 shows how many parameters have to be faken into account, the metal fractions Xa and Xg at the metal surface, fhe cationic and anionic fractions within the film, and fhe dissolution rates of A and B af fhe film surface. Furthermore, the different transfer rates of fhe cations may cause a gradient in the layer composition. Finally, the cations A and B + may be further oxidized at sufficiently positive potentials causing a distribution of lower and higher valent species within the film. This in turn requires the knowledge of the semiconducting properties that are involved in the oxidation of cations as well as the reactions of redox systems at the film surface, which require electron conduction across the layer. All these details show that the semiconductor properties and the chemical composition and structure have to be studied with appropriate tools. The complexity of these systems requires the application of surface analytical methods in order to understand the properties of these films and their influence on the corrosion properties of alloys. 

Hydroxylation of the metal cation may be obtained through an acid-base reaction (neutralization, thermolysis, etc.) or through an oxidation-reduction reaction. The charge-pH diagram (Figure 1.6) shows that reduction and oxidation of cations as 0x0 and aquo species, respectively, allows them to reach the stability domain of hydroxo forms. Hydroxylation is the initiation stage of the process and the hydro-xylated complex is the precursor of the condensation products. 

The oxidation of cationic platinum(II) complexes also can be accomplished with phosphorus pentachloride, Eq. 8.37 ... 

---