Self-oxidation

CaniZZaro Reaction. Both 2- and 4-hydroxybenzaldehydes undergo this self-oxidation—reduction reaction, but much less readily than benzaldehyde the reaction requires metal catalysts such as nickel, cobalt, or silver to yield the corresponding hydroxybenzoic acids and hydroxybenzyl alcohols (47—48). 

Selbst-lbschung, /. (of lime) spontaneous slaking. -I dtung,/. autogenic soldering, -oxyda-tion,/. autoxidation, self-oxidation. 

When chlorine gas is bubbled into a solution of NaOH, self-oxidation-reduction occurs to give hypochlorite ion, CIO-, by the reaction... 

Selenium, ionization energy, 410 Self oxidation-reduction, 361 Separation of charge, 312 Separations by crystallization, 413 by distillation, 70 by precipitation, 176 Seventh column of periodic table, 352... 

The normal reduction potential of the iodine-iodide system is independent of the pH of the solution so long as the latter is less than about 8 at higher values iodine reacts with hydroxide ions to form iodide and the extremely unstable hypoiodite, the latter being transformed rapidly into iodate and iodide by self-oxidation and reduction ... 

The highly evolved catalyst 20 combines several features that have proved successful in simpler cases. The ionic sulfonate groups make the substrate sufficiently soluble for the reaction to be run in water. (The four hydrophilic cyclodextrins perform the same service for the catalyst.) The target reaction, the seledive oxidation of the steroid skeleton, goes back to the early days of enzyme models,1711 and the choice of porphyrin and of manganese as the metal cation are based on many years experience. The aryl groups are perfluorinated because an earlier version of the catalyst suffered self-oxidation. 

Even if the extraction of FeMoco in nmf slightly modifies the outer coordination of the MoFe7S9 cluster, in agreement with the experimental observation that the FeMo-protein can exist in the oxidized, semi-reduced and reduced forms, it exhibits two successive one-electron reductions (E st = -0.32 V and is d = -1.00 V,vj. NHE). In the absence of thio-phenol, the first reduction appears to be complicated by self-oxidation processes, whereas the presence of thiophenol apparently stabilizes the different oxidation states. 

The use of pyrolyzed polyacrylonitrile (PPAN) and polyaniline (PAni) (Fig. 15.8(d), (e)) as catalysts for the ODH of ethylbenzene should only be mentioned here for the sake of completeness. Although first results were quite promising [45], this concept has so far not been followed in terms of N-doped nanocarbon catalyst development. This is most likely due to the poor self-oxidation resistance as a result of polar C-N bonds. 

Figure 4.22(b) shows that no anodic oxidation peaks occurred at lower potential region in alkaline media for marmatite electrode in xanthate and dithiocarbamate solution indicates no formation of collector species on marmatite. When the potential increases to higher potential region, the occurrence of anodic oxidation peak may be due to the self-oxidation of marmatite. It accounts for no flotation of marmatite in alkaline media either using xanthate or dithiocarbamate as collectors. 

Annealed Films. For many years, the CdSe photoelectrode— polysulphide electrolyte PEC— was probably the most studied system in PEC research. The bandgap of (bulk—see later) CdSe is ca. 1.7 eV, which is close to the theoretical optimum of 1.5 eV for photovoltaic cells in general and in relative terms, that system was fairly stable in terms of self-oxidation of the semiconductor fihn in the electrolyte by the photogenerated holes. 

C. W. Bennett and E. L. Mack have shown that the chlorates are oxidized to perchlorates by persulphates and ozone, in acid soln. HC103-t-0=HC104. The self-oxidation of the chlorates to perchlorates 4K0103=3KC104- -KC1, when heated to moderate temp., and the direct oxidation of chlorates by silver oxide observed by J. G. Fowler and J. Grant,17 is evidence of the oxidation of chlorates to perchlorates. 

The combustion of Zn powder in air has been investigated (Ref 18). Owing to the higher vapor pressure of Zn compared with that of Al, ignition temps for Zn are also lower. Complete combustion of Zn powder takes place above 980° whereas the ignition temp for Al powder under the same exptl conditions is 1765° with a combustion temp of 2160—2290°. The process of self-oxidation of Zn dust is stimulated by humidity and the presence of chlorides, whereas the composition of the metallic phase, and the specific surface of the Zn dust were shown to be of minor importance in determining the pyrophoric properties (Ref 19). For a discussion of... 

Bivalent tellurium is not stable and the dichloride in the solid state tends to undergo self-oxidation and reduction, forming a solid solution of the element in the tetrachloride.5 Under the action of water, acids or alkalis, tellurium and tellurous acid are formed ... 

At this stage of the work, two possible explanations can be advanced to rationalize the higher activity of FePcY and the superior stability of FePcVPI-5. As a result of the tubular nature of the pores of VPI-5 and eventual diffusion limitations of the reaction, only the FePc complexes at the external rim of the crystals are active initially but are gradually consumed during reaction. Consequently, FePc complexes located more towards the centre of the crystals become active. Secondly, it can be speculated that the saddle-conformation of FePc in NaY changes the electronic environment of the active iron, thus increasing not only its catalytic activity but also its vulnerability towards self-oxidation. 

A characteristic reaction of aldehydes without a hydrogens is the self oxidation-reduction they undergo in the presence of strong base. With methanal as an example,... 

Here f and f2 represent the bond strength of the Cd-X bond, dictated by bulk crystal structure, and that between the surface Cd and the probably adsorbed, polysulfide species from solution, resp. The larger fj, the more likely it is that the photogenerated hole,h+, will react with the polysulfide species, i.e. the lower the probability of self-oxidation. 

Ans. (a) oxidant (b) reductant (c) both in fact, very small amounts of iron salts in either +2 or +3 oxidation states catalyze the self-oxidation-reduction of H2O2. 

Metallo-phthallocyanine (MePc) complexes are known as mild oxygenation catalysts for alkanes and alkenes and as functional models for enzymes, more in particular for monooxygenases like Cytochrome P450.[44] Among the many possible supports for such complexes, zeolite FAU topologies1451 are excellent materials for their encapsulation. [46 50] The low solubility of Me Pc complexes in general and their tendency to form adducts even in solution, giving rise to self-oxidation and subsequent self-destruction phenomena, make them the ideal candidates for their distribution as individual species on a solid support. 

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