Autoxidation chemistry

A brief overview on why most of the autoxidation reactions develop complicated kinetic patterns is given in Section II. A preliminary survey of the literature revealed that the majority of autoxidation studies were published on a small number of substrates such as L-ascor-bic acid, catechols, cysteine and sulfite ions. The results for each of these substrates will be discussed in a separate section. Results on other metal ion mediated autoxidation reactions are collected in Section VII. In recent years, non-linear kinetic features were discovered in some systems containing dioxygen. These reactions form the basis of a new exciting domain of autoxidation chemistry and will be covered in Section VIII. 

In the development of effective catalytic oxidation systems, there is a qualitative correlation between the desirability of the net or terminal oxidant, (OX in equation 1 and DO in equation 2) and the complexity of its chemistry and the difficulty of its use. The desirability of an oxidant is inversely proportional to its cost and directly proportional to the selectivity, rate, and stability of the associated oxidation reaction. The weight % of active oxygen, ease of deployment, and environmental friendliness of the oxidant are also key issues. Pertinent data for representative oxidants are summarized in Table I (4). The most desirable oxidant, in principle, but the one with the most complex chemistry, is O2. The radical chain or autoxidation chemistry inherent in 02-based organic oxidations, whether it is mediated by redox active transition metal ions, nonmetal species, metal oxide surfaces, or other species, is fascinatingly complex and represents nearly a field unto itself (7,75). Although initiation, termination, hydroperoxide breakdown, concentration dependent inhibition... 

As mentioned with benzyl groups, an allylic center is also quite susceptible to autoxidation chemistry (Fig. 109). The allylic hydrogen has a weak C-H bond dissociation energy due to the resonance stabilization energy of the resulting allylic radical (157). 

Pasiuk-Bronikowska W., T. Bronikowski, K.J. Rudzinski and J. Ziajka Transformations of atmospheric constituents and pollutants indueed by S(IV) autoxidation - chemistry and kinetics, in U. Schurath, J. Peeters, H. Herrmann, D. Poppe (eds). Chemical mechairism development. EUROTRAC-2 CMD Annual Report 2000, EUROTRAC-2 ISS, Munich (2000) 123-126. 

In solution this reaction is rather rapid but in the solid state autoxidation takes place much slower. Nevertheless, commercial sulfides and polysulfides of the alkali and alkali earth metals usually contain thiosulfate (and anions of other sulfur oxoacids) as impurities [6]. For all these reasons the chemistry of polysulfides is rather complex, and some of the earlier studies on polysulfides (prior to ca. 1960) are not very rehable experimentally and/or describe erroneous interpretations of the experimental results. 

Misra, H.P. and Fridovich, I. (1972). The role of superoxide anion in the autoxidation of epinephrine and a simple assay for superoxide dismutase. Journal of Biological Chemistry 247 3170-3175. 

VM Goldberg, LK Obukhova. Progress in Chemistry of Organic Peroxides and Autoxidation. Moscow Khimiya, 1969, p.160 [in Russian]. 

Finally, kinetic and mechanistic studies of autoxidation reactions will not only lead to a better understanding of these essential reactions but also may trigger extensive studies on various areas of dioxygen chemistry. 

A prolific author, Professor van Eldik has been responsible for some 580 papers in refereed journals, and four books as editor or co-editor. His current research intrests are the application of high pressure techniques in mechanistic studies metal-catalyzed autoxidation processes and bioinorganic studies. As such he is eminently qualified to edit the prestigious Advances in Inorganic Chemistry. We are confident that he is a worthy successor to Professor Geoff Sykes and that he will maintain the high standards for which the series is known. 

The ability of organoboron compounds to participate in free radical reactions has been identified since the earliest investigation of their chemistry [1-3]. For instance, the autoxidation of organoboranes (Scheme 1) has been proven to involve radical intermediates [4,5]. This reaction has led recently to the use of triethylborane as a universal radical initiator functioning under a very wide range of reaction conditions (temperature and solvent) [6,7]. 

Parks, O. W. 1974. The lipids of milk Deterioration, Part II. Autoxidation. In Fundamentals of Dairy Chemistry. B.H. Webb, A. H. Johnson and John A. Alford (Editors). AVI Publishing Co., Westport, Conn., pp. 240-263. 

The aldehydes and ketones are least abundant of all the compounds found which may be considered as derived from the fat. The carbonyl compounds are probably produced by an indirect route, which is most likely similar to that involved in autoxidation of a fat. The alkyl free radical can absorb oxygen, form a hydroperoxide, and then follow the many decomposition paths which are familiar in the oxidation chemistry of fats. The more abundant aldehydes found are unsaturated, which further agrees with the hypothesis that they are derived from the decomposition of hydro-... 

Many antioxidants quoted as potential protective agents against free-radical-induced DNA damage have more than one phenolic group. Their chemistry is, therefore, also of some interest in the present context. The semiquinone radicals, derived from hydroquinone by one-electron oxidation or from 1,4-benzoqui-none by one-electron reduction, are in equilibrium with their parents (Roginsky et al. 1999), and these equilibria play a role in the autoxidation of hydroquinone (Eyer 1991 Roginsky and Barsukova 2000). Superoxide radials are intermediates in these reactions. 

The more challenging study is probably the investigation on suspected spontaneous autoxidations, but this is the matter of physical chemistry research. 

The autoxidation of aqueous solutions of sulfur dioxide (sulfite, bisulfite) is a classic problem in chemistry. Basic features of this reaction have been known since early in this century, when it was established that the reaction is trace metal ion catalyzed (1 ) and most likely involves free radicals (2). Certain chemical effects associated with sulfite autoxidation were noted also. Before the turn of the century, it was noted that sulfite would induce the oxidation of transition metal ions (3) and it was reported later that the oxidation of organic compounds was brought about during sulfite autoxidation ( 0. Conversly, organic compounds were also shown to serve as inhibitors of sulfite autoxidation (5). 

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