Total hydroperoxides

Figure 7 Hydroperoxide index (HI) determined from mid-infrared spectroscopy (ratio of the integrated intensity of the 3,552 cm 1 band to the integrated intensity of the band at 2,010 cm-1) as a function of total hydroperoxide content measured by iodiometric titration.

By definition POV is the number of miliequivalents of active oxygen per kilogram of sample" , or in some cases the number of micrograms of active oxygen in one gram of sample, capable of oxidizing iodide to iodine" °°. Many of the methods described in Section V for determination of hydroperoxide classes or individual compounds can also be applied for determination of POV, as total hydroperoxides. The iodometric determination of hydroperoxides in lipids and proteins has been reviewed . 

TOCO see Thiol-olefin co-oxygenation Tocopherols, TEARS assay, 668 Torsion angles, hydroperoxides, 690 Tosylhydrazones, superoxide reactions, 1036 Total hydroperoxides see Peroxide value Total oxidative capacity, titration methods, 674 Total polar phenols, colorimetry, 664 Toxicity... 

Analytical methods for measuring hydroperoxides in fats and oils can be classified as those determining the total amount of hydroperoxides and those based on chromatographic techniques giving detailed information on the structure and the amount of specific hydroperoxides present in a certain oil sample (8). The PV represents the total hydroperoxide content and is one of the most common quality indicators of fats and oils during production and storage (9, 18). A number of methods have been developed for determination of PV, among which the iodometric titration, ferric ion complex measurement spectrophotometry, and infrared spectroscopy are most frequently used (19). 

When u = 0, the CL will decay with time with n-th order kinetics reflecting the decay of the particular fraction of the total hydroperoxide that results in CL. This decay of CL is seen when the polymer is heated in nitrogen (9). 

Polymeric hydroperoxides are the major product of low temperature oxidation [Refs. 46, 113,115, 148, 189, 191, 193,195,196, 300]. Yields of hydroperoxides in oxidized polypropylene exceed 40%, and more than half that amount is contained in low molecular weight degradation products. It was shown that isolated hydroperoxide groups in thermally oxidized polypropylene constitute less than 10% of the total hydroperoxide concentration, and the majority of the polypropylene hydroperoxide groups occur in dimers, trimers, or longer sequences [148]. 

X-OOH = other hydroperoxides, remaining from total hydroperoxide subtracted by PCOOH and AMVN-OOH. 

Chemiluminescent evaluation of peroxide value in olive oil. Talanta 65 1056-1058. Tsiaka, T., D. C. Christodouleas, and A. C. Calokerinos. 2013. Development of a chemiluminescent method for the evaluation of total hydroperoxide content of edible oils. Food Res. Int. 54 2069-2074. 

This procedure may result in a concentration of cumene hydroperoxide of 9—12% in the first reactor, 15—20% in the second, 24—29% in the third, and 32—39% in the fourth. Yields of cumene hydroperoxide may be in the range of 90—95% (18). The total residence time in each reactor is likely to be in the range of 3—6 h. The product is then concentrated by evaporation to 75—85% cumene hydroperoxide. The hydroperoxide is cleaved under acid conditions with agitation in a vessel at 60—100°C. A large number of nonoxidising inorganic acids are usehil for this reaction, eg, sulfur dioxide (19). 

An oxirane process utilizes ethylbenzene to make the hydroperoxide, which then is used to make propylene oxide [75-56-9]. The hydroperoxide-producing reaction is similar to the first step of cumene LPO except that it is slower (2,224,316—318). In the epoxidation step, a-phenylethyl alcohol [98-85-1] is the coproduct. It is dehydrated to styrene [100-42-5]. The reported 1992 capacity for styrene by this route was 0.59 X 10 t/yr (319). The corresponding propylene oxide capacity is ca 0.33 x 10 t/yr. The total propylene oxide capacity based on hydroperoxide oxidation of propylene [115-07-1] (coproducts are /-butyl alcohol and styrene) is 1.05 x 10 t/yr (225). 

The acetone supply is strongly influenced by the production of phenol, and so the small difference between total demand and the acetone suppHed by the cumene oxidation process is made up from other sources. The largest use for acetone is in solvents although increasing amounts ate used to make bisphenol A [80-05-7] and methyl methacrylate [80-62-6]. a-Methylstyrene [98-83-9] is produced in controlled quantities from the cleavage of cumene hydroperoxide, or it can be made directly by the dehydrogenation of cumene. About 2% of the cumene produced in 1987 went to a-methylstyrene manufacture for use in poly (a-methylstyrene) and as an ingredient that imparts heat-resistant quaUties to polystyrene plastics. 

These include the mitochondrial respiratory chain, key enzymes in fatty acid and amino acid oxidation, and the citric acid cycle. Reoxidation of the reduced flavin in oxygenases and mixed-function oxidases proceeds by way of formation of the flavin radical and flavin hydroperoxide, with the intermediate generation of superoxide and perhydroxyl radicals and hydrogen peroxide. Because of this, flavin oxidases make a significant contribution to the total oxidant stress of the body. 

Inspired by Gif or GoAgg type chemistry [77], iron carboxylates were investigated for the oxidation of cyclohexane, recently. For example, Schmid and coworkers showed that a hexanuclear iron /t-nitrobenzoate [Fe603(0H) (p-N02C6H4C00)n(dmf)4] with an unprecedented [Fe6 03(p3-0)(p2-0H)] " core is the most active catalyst [86]. In the oxidation of cyclohexane with only 0.3 mol% of the hexanuclear iron complex, total yields up to 30% of the corresponding alcohol and ketone were achieved with 50% H2O2 (5.5-8 equiv.) as terminal oxidant. The ratio of the obtained products was between 1 1 and 1 1.5 and suggests a Haber-Weiss radical chain mechanism [87, 88] or a cyclohexyl hydroperoxide as primary oxidation product. 

Organic peroxides and hydroperoxides decompose in part by a self-induced radical chain mechanism whereby radicals released in spontaneous decomposition attack other molecules of the peroxide.The attacking radical combines with one part of the peroxide molecule and simultaneously releases another radical. The net result is the wastage of a molecule of peroxide since the number of primary radicals available for initiation is unchanged. The velocity constant ka we require refers to the spontaneous decomposition only and not to the total decomposition rate which includes the contribution of the chain, or induced, decomposition. Induced decomposition usually is indicated by deviation of the decomposition process from first-order kinetics and by a dependence of the rate on the solvent, especially when it consists of a polymerizable monomer. The constant kd may be separately evaluated through kinetic measurements carried out in the presence of inhibitors which destroy the radical chain carriers. The aliphatic azo-bis-nitriles offer a real advantage over benzoyl peroxide in that they are not susceptible to induced decomposition. 

An interesting multicomponent domino free radical reaction in which five new bonds are formed in one operation has recently been applied in the total synthesis ofyingzhaosu A by Bachi and coworkers. Thus, a 2,3-dioxabicyclo[3.3.1]nonane system reacts with phenylthiol and 2 equiv. of molecular oxygen in the presence of AIBN, which under irradiation with UV light led to a diastereomeric mixture of en-doperoxide-hydroperoxides [127]. 

Figure 1 The theoretical plot of induction time of oxidation determined for wr — 0, (zero rate of initiation according to reaction 1 of Scheme 1) on composition of the mixture of inhibitors InH (chain-breaking antioxidant) and D (peroxide decomposer) having the total sum of concentrations 0.01 mol/l. The curve 2 below is the plot of induction times for the same values of parameters as for line 1 but w, = 5 x 10-8 mol/l. The initial concentration of hydroperoxides was 0.001 mol/l.

The accumulation of hydroxyl-containing products, such as hydroperoxides, alcohols, acids, and water, also reduce the total activity of peroxyl radicals due to the hydrogen bonding with R02 [150], When acting together, these factors cause self-inhibition of autoxidation at conversion levels of 40-50% [3],... 

Lipid peroxidation is probably the most studied oxidative process in biological systems. At present, Medline cites about 30,000 publications on lipid peroxidation, but the total number of studies must be much more because Medline does not include publications before 1970. Most of the earlier studies are in vitro studies, in which lipid peroxidation is carried out in lipid suspensions, cellular organelles (mitochondria and microsomes), or cells and initiated by simple chemical free radical-produced systems (the Fenton reaction, ferrous ions + ascorbate, carbon tetrachloride, etc). In these in vitro experiments reaction products (mainly, malon-dialdehyde (MDA), lipid hydroperoxides, and diene conjugates) were analyzed by physicochemical methods (optical spectroscopy and later on, HPLC and EPR spectroscopies). These studies gave the important information concerning the mechanism of lipid peroxidation, the structures of reaction products, etc. 

Schnurr et al. [22] showed that rabbit 15-LOX oxidized beef heart submitochondrial particles to form phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids and induced the oxidative modification of membrane proteins. It was also found that the total oxygen uptake significantly exceeded the formation of oxygenated polyenoic acids supposedly due to the formation of hydroxyl radicals by the reaction of ubiquinone with lipid 15-LOX-derived hydroperoxides. However, it is impossible to agree with this proposal because it is known for a long time [23] that quinones cannot catalyze the formation of hydroxyl radicals by the Fenton reaction. Oxidation of intracellular unsaturated acids (for example, linoleic and arachidonic acids) by lipoxygenases can be suppressed by fatty acid binding proteins [24]. 

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