Autooxidation reaction

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... 

The use of models that mimic a protein active site is normally prompted by the desire to eliminate any influence of the polypeptide backbone surrounding the active site in real biological molecules, which may obscure its physico-chemical properties. The first attempts to synthesize metal complexes similar to the active site of haemoproteins, through the use of simple metalloporphyrin derivatives, failed. The failure was due to the fact that these complexes react irreversibly with dioxygen as a consequence of side autooxidative reactions of the type ... 

Consider any organic molecule, which we will call R-H, where / could be an alkyl or any fragment containing C, H, and 0 atoms. In the presence of O2 this molecule can undergo the autooxidation reaction... 

Both biological reactions and autooxidation reactions in food are complex problems because both are highly autocatalytic. Their occurrence is therefore very variable between nominally identical samples of food. When a reaction is both unpredictable and intolerable, the chemical engineer must be especially alert. 

The main features of this hydroperoxidation reaction are that in any case a shift of the double bond is connected with this reaction, and that no free radicals are involved i.e., no hydrogen abstraction from the carbon atom a to the double bond prior to the C—O bond formation occurs as is the case in the well-studied autooxidation reactions. In the latter reactions two different hydroperoxides are formed as... 

In this context, homolytical oxidation reactions (autooxidation) proceeding by the free-radical mechanism seem to be the most suitable model. In autooxidation reactions ROOH dissociation catalysis (in the most reduced case, H202) plays the key role, but does not eliminate selectivity. This is the most urgent problem of homolytical oxidation. 

Figure 12. Direct P-450 type oxidation, Reaction 5 TPP Mn autooxidation, Reaction 6...

Numerous types of stirrers are used in practice, and Fig. 3.2 shows the most commonly used ones. The stirrers for low-viscosity media are typically marine propeller and pitched-blade turbine stirrers, which cause axial fluid motion, and flat-blade turbines and impellers, which generate radial fluid motion. The former stirrers are suitable for uniformly suspending solids. The latter type are the preferred ones for carrying out exothermic reactions, like autooxidation reactions (see Section 8.3), where the heat generated dining the process has to be removed effectively through the reactor walls. 

The oxidized iron travels from the ferroxidase center to the core, thus regenerating the ferroxidase center for finther reactions. When large amounts of iron are added (>800 Fe per protein), following oxidation of the first two ferrous ions per subunit an autooxidation reaction catalyzed by the core surface takes over and becomes the predominant mechanism (equation 5) ... 

From a practical point of view the study of the chemistry of dioxygen complexes has considerable interest. Complexation of molecular oxygen by a transition metal has been widely adopted by biological systems as a means of reducing the considerable kinetic barrier to the reduction of O2. Quite apart from the inherent interest of the biological systems, the transition metal complexes offer the possibility of efficient catalysis of autooxidation reactions, and have recently attracted interest as possible catalysts for the reduction of O2 in fuel cells ... 

Photo-oxidation has been reported at crude-oU spills. It results in depletion of n-aUcanes below nCi5 and alkylaromatics such as C - and C2-substituted naphthalenes relative to unoxidized oil (Payne and Phillips, 1985). In terms of a material balance, photo-oxidation has been found to be a minor process (NRC, 1985) but does result in changes in the residual oil composition and can affect the subsequent behavior of an oil spill on the open ocean (Payne and Phillips, 1985). Autooxidation reactions of hydrocarbons in the absence of hght have not been well studied. 

Molecular oxygen can also oxidize a variety of organic compounds, including hydrocarbons, aldehydes, amines, ethers and ketones. These autooxidation reactions can be used to make a variety of small molecules and a number of industrial processes rely on the controlled oxidation of organics using molecular oxygen (often with a metal catalyst). Examples include the formation of phenol and acetone from cumene (isopropylbenzene) and cyclohexanone from cyclohexane. Phenol is a popular starting material for a number... 

Autooxidation reactions have also been used as Oj-generating systems. Substances that have been utilized as autooxidizing systems include adrenalin (M23.S19), sulfite, pyrogallol (M3), and 6-hydroxydopamine (Hll). Direct addition of K+Oj as an O generator has also been reported (M4). Illuminated riboflavin (Bll) is another source of Oj. 

Stable free radicals are of particular importance to those who are engaged in polymer stabilization because they play a key role in the inhibition of autooxidation reactions. 

The mechanisms of autooxidation reactions were elucidated through the landmark research carried out at the British Rubber Producers Research Association, where the kinetics of autooxidation of olefins were studied in the 1940 s and early 1950 s. Some of the key researchers engaged in that work were L. Bateman, J. L. Bolland, G. Gee, A. L. Morris, P. Ten Have, among others. They contributed enormously to our understanding of autooxidation reactions of organic materials. Re-reading their papers produces appreciation of their important work and emphasizes the debt we, in polymer stabilization work, owe them. That work established the following ... 

Figure 4.5. Idealized kinetics for a typical autooxidation reaction. From Ranby and Rabek (1975). Reprinted by permission of John Wiley and Sons.

Some of the reactions of peroxy radicals were discussed in Section A.l of this chapter during our analysis of autooxidation reactions. These reactive intermediates also undergo many other processes of great importance in natural systems and also in treatment systems where high concentrations of free radicals are generated. 

Movement of electrons between energetically equivalent positions [122, 123] or in the presence of oxygen by the autooxidative reaction cycle, R + O2 ROO and ROD -h RH ROOH + R. ... 

Any Schiff s base formation in a perfume itself is brought about by the deliberate inclusion of methyl anthranilate in the mixture. Work published almost 50 years ago by Wells [13] reviews some interesting Schiff s compounds of use to the perfumer. For the chemist, it is important to note that the formation of a Schiff s base can be quite slow and the compounds can be highly colored. Perfume oils delivered to a detergent manufacturer will be stable and matured, such that the consequences of the reactions reviewed in this section should be somewhat academic. However, autooxidation reactions such as... 

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