Oxidant formation mechanism

Ghiorse.W.E. (2002) Effed of oxide formation mechanisms on lead adsorption by biogenic manganese hydroxides and their mixtures. Environ. Sci. Techn. 36 421-425 Nembrini, G. Buffle, J. Haerdi, W. (1976) Vol-tametric behavior of iron(III) hydrolyzed solutions and characterization of the reducible species. J. Colloid Interface Sci. 57 327-336 Nesson, M.H. Lowenstam, H.A. (1985) Biomineralization proceses of radula teeth of chitons. In Kirschvink, J.L. Stone, D.S. (eds.) Magnetite biomineralization and magneto reception in organisms. Plenum Press, New York, 333-363... 

Nelson, Y.M. et al., Effect of oxide formation mechanisms on lead adsorption by biogenic manganese (hydr)oxides, iron (hydr)oxides, and their mix lures, Environ. Sci. Technol., 36, 421, 2002. 

Combustion characteristics of consequence include the overall mechanism of soHd waste combustion, factors governing rates of waste fuels combustion, temperatures associated with waste oxidation, and pollution-formation mechanisms. 

The hterature suggests that more than one mechanism may be operative for a given antiozonant, and that different mechanisms may be appHcable to different types of antiozonants. All of the evidence, however, indicates that the scavenger mechanism is the most important. All antiozonants react with ozone at a much higher rate than does the mbber which they protect. The extremely high reactivity with ozone of/)-phenylenediamines, compared to other amines, is best explained by their unique abiUty to react ftee-tadicaHy. The chemistry of ozone—/)-PDA reactions is known in some detail (30,31). The first step is beheved to be the formation of an ozone—/)-PDA adduct (32), or in some cases a radical ion. Pour competing fates for dissociation of the initial adduct have been described amine oxide formation, side-chain oxidation, nitroxide radical formation, and amino radical formation. 

Consider Ni exposed to Oj/HjO vapour mixtures. Possible oxidation products are NiO and Ni (OH)2, but the large molar volume of Ni (OH)2, (24 cm compared with that of Ni, 6.6 cm ) means that the hydroxide is not likely to form as a continuous film. From thermodynamic data, Ni (OH)2 is the stable species in pure water vapour, and in all Oj/HjO vapour mixtures in which O2 is present in measurable quantities, and certainly if the partial pressure of O2 is greater than the dissociation pressure of NiO. But the actual reaction product is determined by kinetics, not by thermodynamics, and because the mechanism of hydroxide formation is more complex than oxide formation, Ni (OH)2 is only expected to form in the later stages of the oxidation at the NiO/gas interface. As it does so, cation vacancies are formed in the oxide according to... 

Where caustic deposits occur, the resultant corrosion of steel by caustic gouging or stress corrosion cracking (SCC) mechanisms produces particulate iron oxides of hematite and magnetite. It is common to see white rings of deposited sodium hydroxide around the area of iron oxide formation. 

Oxidant Formation. The role of HO. in controlling the time-scale and severity of tropospheric oxidant pollution may be seen from the parameterization of O Brien and co-workers (75,76). The simplest possible mechanism for oxidant (Le. ozone, PAN, H2O2, etc.) formation consists simply of the reaction of an individual NNlHCj with HO. to convert the NMHCj to a generic product(s) PRODj, followed by removal of the product by HO. (PROD photolysis may be important, but is ignored here)... 

When combined with reactions R13 and R14-R16 (the PSS), this highly simplified mechanism describes the elements of ozone and other oxidant formation. By defining net ozone [O3-NO.] it is recognized that oxidant... 

Figure 9.6 Visual representation of the platinum oxide growth mechanism, (a) Interaction of H2O molecules with the Pt electrode occurring in the 0.27 V < < 0.85 V range, (b) Discharge of 5 ML of H2O molecules and formation of 5 ML of chemisorbed oxygen (Ochem)- (c) Discharge of the second ML of H2O molecules the process is accompanied by the development of repulsive interactions between (Pt-Pt) -Ofi m surface species that stimulate an interfacial place exchange of Ochem and Pt surface atoms, (d) Quasi-3D surface PtO lattice, comprising Pt and moieties, that forms through the place-exchange process. (Reproduced with permission...

Basically, three reactions were evoked to support the occurrence of 5a-C-centered radicals 10 in tocopherol chemistry. The first one is the formation of 5a-substituted derivatives (8) in the reaction of a-tocopherol (1) with radicals and radical initiators. The most prominent example here is the reaction of 1 with dibenzoyl peroxide leading to 5a-a-tocopheryl benzoate (11) in fair yields,12 so that a typical radical recombination mechanism was postulated (Fig. 6.6). Similarly, low yields of 5a-alkoxy-a-tocopherols were obtained by oxidation of a-tocopherol with tert-butyl hydroperoxide or other peroxides in inert solvents containing various alcohols,23 24 although the involvement of 5 a-C-centered radicals in the formation mechanism was not evoked for explanation in these cases. 

The oxidation of a-tocopherol (1) to dimers29,50 and trimers15,51 has been reported already in the early days of vitamin E chemistry, including standard procedures for near-quantitative preparation of these compounds. The formation generally proceeds via orf/zo-quinone methide 3 as the key intermediate. The dimerization of 3 into spiro dimer 9 is one of the most frequently occurring reactions in tocopherol chemistry, being almost ubiquitous as side reaction as soon as the o-QM 3 occurs as reaction intermediate. Early accounts proposed numerous incorrect structures,52 which found entry into review articles and thus survived in the literature until today.22 Also several different proposals as to the formation mechanisms of these compounds existed. Only recently, a consistent model of their formation pathways and interconversions as well as a complete NMR assignment of the different diastereomers was achieved.28... 

Does anion incorporation influence the oxide formation, and what is the mechanism of anion pickup ... 

Niederberger, M., Gamweitner, G., Pinna, N. and Neri, G. (2005) Non-aqueous routes to crystalline metal oxide nanopartides formation mechanisms and applications. Progress in Solid State Chemistry, 33 (2—4), 59—70. 

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