Free radical oxidation processes

Guy C, Benali M, Ostigny E. Free radical oxidation process and installation for treating liquid effluents contaminated by organic substances. U.S. Patent No. 5,641,412, 1997. 

Table 1. Effect of tiecrezan on free-radical oxidative processes under the action of cblotophos.

To study free radical formation in a beer sample a spin trapping agent is added to the beer and incubated at 60 °C. This forced aging accelerates the free radical oxidation process to a... 

For the last quarter of the century there was a considerable quantity of works devoted to research of the activity of antioxidants (AO) in herbs, foodstuff, drinks, biological liquids, and other objects. It is known that the increase in activity of free radical oxidation processes in a htrman organism leads to destruction of stmcture and properties of lipid membranes. There is a direct commrmication between the superfluous content of free radicals in an organism and occtrrrence of dangerous diseases [1,2]. The AO are class of biologically active substances which remove excessive free radicals, decreasing the lipid oxidation. Therefore, a detailed research of the total antioxidant activity of various biological objects represents doubtless interest. 

The basic free-radical oxidation process that is used to interpret polymer coating photooxidation kinetics has been described in detail and is presented briefly below ... 

The reaction (6.10) is the initial step of the development of the chain free-radical oxidation process. The radical R, which is created in the reaction, once again goes to the reaction (6.9), but hydroperoxide ROOH can decompose according to the radical mechanism depending on... 

The effect on the ageing of ethylene-vinyl acetate copolymer has been studied [46]. Mechanisms are suggested for the formation of the various oxidative groups found. Combinations of phenolic antioxidants with phosphates give greatest protection against discolouration, which is consistent with a proposed free radical oxidation process of deacetylation. 

In terms of stabilisation against discolouration, primary phenolic antioxidants exhibit some inhibition activity whereas combinations with phosphites can display powerful synergism. This is consistent with the involvement of a free radical oxidation process in deacetylation through ketone/hydroperoxide initiation. 

The scope of oxidation chemistry is enormous and embraces a wide range of reactions and processes. This article provides a brief introduction to the homogeneous free-radical oxidations of paraffinic and alkylaromatic hydrocarbons. Heterogeneous catalysis, biochemical and hiomimetic oxidations, oxidations of unsaturates, anodic oxidations, etc, even if used to illustrate specific points, are arbitrarily outside the purview of this article. There are, even so, many unifying features among these areas. 

Degenerate Explosion it was a free radical autocatalytic process and control was difficult, but manageable. The main disadvantage was that it produced as much or more acrolein as propylene oxide. Because no market existed for acrolein at that time, the project was abandoned. Within two years, the acrylic market developed and a new project was initiated to make acrolein and acrylic acid by vapor-phase catalytic oxidation of propylene. 

Note, Added in Proof-. In their study of the autoxidation of 2-butyl-isoindoline, Kochi and Singleton showed that 2-butylisoindole is formed and is converted by further oxidation to 2-butylphthalimide and 2-butylphthalimidine. The rate of oxidation of 2-butylisoindoline to the isoindole was found to be markedly dependent on hydrogen donor ability of the solvent and was shoivn to involve a free radical chain process. Autoxidation of 2-butylisoindole also appears to be a radical process since it can initiate autoxidation of 2-butylisoindoline. 

Scheme 1 Free radical chain process involved in polymer oxidation.

The decompositions of hydroperoxides (reactions 4 and 5) that occur as a uni-or bimolecular process are the most important reactions leading to the oxidative degradation (reactions 4 and 5). The bimolecular reaction (reaction 5) takes place some time after the unimolecular initiation (reaction 4) provided that a sufficiently high concentration of hydroperoxides accumulates. In the case of oxidation in a condensed system of a solid polymer with restricted diffusional mobility of respective segments, where hydroperoxides are spread around the initial initiation site, the predominating mode of initiation of free radical oxidation is bimolecular decomposition of hydroperoxides. 

The modification of amino acids in proteins and peptides by oxidative processes plays a major role in the development of disease and in aging (Halliwell and Gutteridge, 1989, 1990 Kim et al., 1985 Tabor and Richardson, 1987 Stadtman, 1992). Tissue damage through free radical oxidation is known to cause various cancers, neurological degenerative conditions, pulmonary problems, inflammation, cardiovascular disease, and a host of other problems. Oxidation of protein structures can alter activity, inhibit normal protein interactions, modify amino acid side chains, cleave peptide bonds, and even cause crosslinks to form between proteins. 

Figure 2.6 Anthraquinone derivatives can photoreactively couple to substrates by means of a free radical generation process. The reactive intermediate also can be regenerated back to the initial anthraquinone by proton abstraction and oxidation, resulting in the possibility of again being photolyzed and successfully coupled to the substrate.

There are various pathways for free radical-mediated processes in microsomes. Microsomes can stimulate free radical oxidation of various substrates through the formation of superoxide and hydroxyl radicals (the latter in the presence of iron) or by the direct interaction of chain electron carriers with these compounds. One-electron reduction of numerous electron acceptors has been extensively studied in connection with the conversion of quinone drugs and xenobiotics in microsomes into reactive semiquinones, capable of inducing damaging effects in humans. (In 1980s, the microsomal reduction of anticancer anthracycline antibiotics and related compounds were studied in detail due to possible mechanism of their cardiotoxic activity and was discussed by us earlier [37], It has been shown that semiquinones of... 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

Apart from specifications as to origin, e.g. palm kernel oil, fats are normally supplied on the basis of established parameters. One of these is the iodine value. This reflects the tendency of iodine to react with double bonds. Thus, the higher the iodine value the more saturated the fat is. An iodine value of 86 would approximate to one double bond per chain, while an iodine value of 172 approximates to two double bonds per chain. Another parameter is the peroxide value. This attempts to measure the susceptibility of the fat or oil to free radical oxidation. The test is applied on a freshly produced oil and measures the hydroperoxides present. These hydroperoxides are the first stage of the oxidation process. Obviously, this test would not give reliable results if applied on a stale sample. 

Balance equations, for a mixture, 24 669-671 Balances 26 227 analytical, 26 245 precision, 26 245 Balke process, 17 139 B-Alkyl-9-BBN derivatives, 13 658 B-Alkylcatecholboranes, free-radical oxidations of, 13 648 Ball and chain structures, fullerene, 12 252... 

It has been shown that the influence of photoexcited fullerene C60 on the processes of free-radical oxidation depends on the type of the cell and on the composition of composite. So, in thymocytes in the presence of photoexcited fullerene C60 as well as fullerene C60-containing composites, the content of primary and final LPO products did not alter compared to the control. In malignant cells the intensification of LPO processes was registered, and its level depends on the type of cells. So, in thymocytes in the presence of photoexcited fullerene C60 in suspension of EAC cells the decrease in the content of diene conjugates simultaneously with the increase in the... 

Most free radicals contain odd numbers of electrons and most stable molecules contain even numbers of electrons (nitric oxide and nitrogen dioxide are two important exceptions being stable molecules with odd numbers of electrons). Therefore in the reaction, free radical + stable molecule % another free radical is usually generated. This free-radical diain process is stopped only when one of the following types of processes occurs ... 

McMahon PB, Chapelle FH, Falls WF, Bradley PM (1992) Role of microbial processes in linking sand stone diagenesis with organic-rich clay. J Sedimen Petrol 62 1-10 Mill T, Hendry DG, Richardson H (1980) Free radical oxidants in natural waters. Science... 

The use of zeolites can overcome many of these limitations and provide new controlled entries into these oxidized hydrocarbons and new materials. For example, some of the most valuable industrial intermediates are terminally oxidized hydrocarbons, snch as n-hexanol or adipic acid, that are not readily available in free-radical chain processes. The ability of zeolites to function as shape-selective catalysts can, in principle, be used to restrict access, by reactant or transition state selectivity, to sites not normally attacked by oxidants [3]. 

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