Initiation reaction with oxygen

The primary oxidation product, hydroperoxide ROOH, decomposes by scission of the oxygen-oxygen bond to produce two radicals which can subsequently initiate reaction with oxygen. 

One-electron reduced cyt c oxidase oxidizes cyt c(ii) with a second-order rate of 5 x 10 M s at pH 7.4 and 25 °C, The presence of CO inhibits the reaction but the catalytic activity of the enzyme in the presence of oxygen is the same as the resting or fully reduced species. A rapid initial reaction with oxygen with a second-order rate constant of 1 x 10 s has been measured. ... 

Lead is one of the most stable of fabricated materials because of excellent corrosion resistance to air, water, and soil. An initial reaction with these elements results in the formation of protective coatings of insoluble lead compounds. For example, in the presence of oxygen, water attacks lead, but if the water contains carbonates and siUcates, protective films or tarnishes form and the corrosion becomes exceedingly slow. 

Combustion has a very long history. From antiquity up to the middle ages, fire along with earth, water, and air was considered to be one of the four basic elements in the universe. However, with the work of Antoine Lavoisier, one of the initiators of the Chemical Revolution and discoverer of the Law of Conservation of Mass (1785), its importance was reduced. In 1775-1777, Lavoisier was the first to postulate that the key to combustion was oxygen. He realized that the newly isolated constituent of air (Joseph Priestley in England and Carl Scheele in Sweden, 1772-1774) was an element he then named it and formulated a new definition of combustion, as the process of chemical reactions with oxygen. In precise, quantitative experiments he laid the foundations for the new theory, which gained wide acceptance over a relatively short period. 

A strain of Escherichia coli produces a naphthotriazole from 2,3-diaminonaphthalene and nitrite that is formed from nitrate by the action of nitrate reductase. The initial product is NO, which is converted by reactions with oxygen into the active nitrosylating agent that reacts chemically with the amine (Ji and Hollocher 1988). A comparable reaction may plausibly account for the formation of dimethylnitrosamine by Pseudomonas stutzeri during growth with dimethylamine in the presence of nitrite (Mills and Alexander 1976) (Figure 2.2f). 

However, the initial absence of unstable groups is no guarantee for long-term stability of the compound. For example, some aldehydes and ethers are easily converted to peroxides by reaction with oxygen from air [35,37,38]. Organic peroxides represent a class of unstable materials while monomers represent a class of substances that can self-react by polymerization if not properly inhibited and if the temperature is not properly maintained. Runaway reactions can result in both of these examples. 

The photo-oxidation reactions are the last two in the scheme - these are listed as reactions G and T. In the former reaction, the initial radical abstraction is performed by pretty much any radical available in the polymer matrix. Reaction with oxygen to form the hydroperoxy radical followed by hydrogen abstraction to form a hydroperoxide has been suggested as a mechanism of gylcol oxidation [11, 25, 31] and is, of course, a very reasonable reaction path. Note that the... 

The intrinsic reactivity of pyridine 1-oxides toward nucleophiles is little greater than that of pyridine the strongest nucleophiles react. However, after initial reaction with an electrophile at the N-oxide oxygen, subsequent attack by nucleophiles is easy see above discussion under cationic rings . 

The mechanisms behind lipid oxidation of foods has been the subject of many research projects. One reaction in particular, autoxida-tion, is consistently believed to be the major source of lipid oxidation in foods (Fennema, 1993). Autoxidation involves self-catalytic reactions with molecular oxygen in which free radicals are formed from unsaturated fatty acids (initiation), followed by reaction with oxygen to form peroxy radicals (propagation), and terminated by reactions with other unsaturated molecules to form hydroperoxides (termination O Connor and O Brien, 1994). Additionally, enzymes inherent in the food system can contribute to lipid oxidization. 

A procedure for the preparation of finely divided MnO is to alternate layers of vermiculite and manganous oxalate in a column similar to that shown in Fig. 3.4. Initial activation is performed by heating the evacuated column to 330°C for 6 h. The resulting green MnO is pyrophoric and must not be exposed to a sudden inrush of air. The predominant reaction with oxygen, Eq. (2), results in a brown-black product so visual inspection of the column readily indicates its degree of... 

This ion is not reactive with H2 but can react with a number of other heavy atoms assumed to be present in initial stages of the cloud. In particular, reaction with oxygen atoms leads eventually to the production of the molecular ion H30+ by a chain of exothermic ion-molecule reactions studied in the laboratory ... 

The definition of an antioxidant suggests a functional assay of antioxidants by measuring inhibition of appropriate (easy to study) oxidation reactions. Such assays can be called inhibition assays for antioxidants (Fig. 2). Various oxidants are used in TAC assays. In many cases, thermal decomposition of 2,2 -azobis (2-amidopropane) (ABAP) is the source of oxidizing radicals. ABAP undergoes temperature-dependent homolysis. The primary radicals produced by thermal decomposition of the initiator react with oxygen to produce peroxyl and alkoxyl radicals, which are oxidizing species in the system (Fig. 3). The amount of free radicals formed in an aqueous medium by decomposition of ABAP at pH 7.4 and at 37°C equals 1.36 x 10-6 [ABAP] x t, where t is time in seconds and [ABAP] is in mol L-1 (N8). 

On the other hand, some evidence for the longer life-time of the intermediate formed with amines may be inferred from the formation of small amounts of (116a) from piperidine and /J-chloroacrylonitrile, in addition to the main substitution product. (116a) is also the sole substitution product with aniline (R1=Ph, R2 = H) but no such products were reported for reactions with oxygen or sulphur nucleophiles. For formation of (116a) the initially-formed carbanion should be long-lived enough as to attack another j8-chloroacrylonitrile molecule (Scotti and Frazza, 1964). 

As both reactions (2.37) and (2.19) lead to the oxidation of NO to NO2 the subsequent photolysis leads to the formation of ozone (see reactions (2.2) and (2.20)). The individual reaction mechanism depends on the identity of the organic compounds and the level of complexity of the mechanism. Although OH is the main tropospheric oxidation initiator, reaction with NO3, O3, 0( P) or photolysis may be an important loss route for some NMHCs or the partially oxygenated products produced as intermediates in the oxidation (see reaction (2.38)). 

Carbon dioxide is produced in petrochemical process streams by reactions with oxygenates (mainly oxygen or water). In steam cracking, hydrocarbons (e.g. methane) and carbon react with steam, forming initially carbon monoxide which is then converted into carbon dioxide by the water-gas-shift reaction ... 

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