Hydroperoxide chemical structures

The only gas-phase chemical reactions reported for excited 02, other than with 03, are reactions with olefinic substances.24 38 44,50,51 The reactjon of 02(1A9) with 2,3-dimethylbutene-2 (TME) has been discussed in Section III-F in connection with techniques for the estimation of [02(1Afl)], and the preliminary rate constant of 10s liter mole-1 sec-1, obtained by Arnold44 has been reported. She investigated the removal of Q2(1A9) by a series of olefins Figure 6 shows the decay of [O A,)] in the presence of equal concentrations of ethylene and five of its derivatives. Presumably all the olefins may react initially to form hydroperoxides (see structure 1, p. 328), although their relative stabilities may explain why 2,3-dimethylbutene-2 is so much more effective in removing 02(1A9) than are the other olefins. 

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

A constant observation when the MRP were separated by various methods was that antioxidative effect was found in many different fractions. Both the dialysates and the retentates from dialysis were antioxidative to some extent. All the electrophoresis fractions exhibited some antioxidative effect. Attempts to separate the MRP by column chromatography on Sephadex G-50 have resulted in several fractions with some antioxidative effect, and so on. This indicates that several antioxidative products are formed by the Maillard reaction, possibly differing in molecular size and chemical structure, but perhaps with one single antioxidative functional group in common, such as a free radical function. However, it can not be excluded that the MRP contain a few entirely different antioxidants with different modes of action. Various mechanisms have also been suggested. Eichner (6) claimed MRP to inactivate the hydroperoxides formed by the lipid oxidation. There are also reports on the complex binding of metals by MRP (18, 19). 

Hydrogen atoms in allylic position are favorite sites for hydroperoxidation of chains. So, this mechanism proceeds in the formation of lateral hydroperoxides, and not like for other polymers, in intramolecular peroxides. Rearrangement of chemical structures coming from ozonides are rapidly observed (Scheme 33). 

By AFM analysis, it was shown that the modifications of the surface aspect can be characterized as a function of the irradiation time using the roughness parameters. A correlation between the modifications of the surface and the modifications of the chemical structure of the macromolecules resulting from irradiation showed that the degradation of the surface depends essentially on the decomposition of the hydroperoxides. 

Chemical structure of hydroperoxide forming the initial complex. This alters the structure and spin state of the Fe" + complex and, consequently, affects dominant product pathways (73). H2O2 forms low spin complexes that undergo heterolytic scission, whereas alkyl hydroperoxides form high spin complexes that release alkoxyl radicals in homolytic scissions (81). 

Synonyms 2-Hydroperoxy-2-methylpropane 1,1-Dimethylethyl hydroperoxide TBHP, TBH Chemical/Pharmaceutical/Other Class Peroxides Chemical Formula C4H10O2 Chemical Structure ... 

The main function of metal deactivators (MD) is to retard efficiently metal-catalyzed oxidation of polymers. Polymer contact with metals occur widely, for example, when certain fillers, reinforcements, and pigments are added to polymers, and, more importantly when polymers, such as polyolefins and PVC, are used as insulation materials for copper wires and power cables (copper is a pro-oxidant since it accelerates the decomposition of hydroperoxides to free radicals, which initiate polymer oxidation). The deactivators are normally poly functional chelating compounds with ligands containing atoms like N, O, S, and P (e.g., see Table 1, AOs 33 and 34) that can chelate with metals and decrease their catalytic activity. Depending on their chemical structures, many metal deactivators also function by other antioxidant mechanisms, e.g., AO 33 contains the hindered phenol moiety and would also function as CB-D antioxidants. 

Long-chain unsaturated oils such as fatty acid esters are used in a number of semisolid and liquid products. It is known from the use of these oils that the double bonds in their chemical structure can react with oxygen to form peroxides and/or hydroperoxides. Some compendial monographs for these materials will have specifications to limit the level of peroxide for this reason. For active ingredients that are easily oxidized, these excipients may need to be avoided to minimize the catalytic oxidation of the active ingredient and to maximize the stability of the drug product. 

Sulphur/nitrogen and sulphur/phosphorus compounds Other multifunctional sulphur/nitrogen, sulphur/phosphorus-based additives have antioxidant and antiwear properties. These additives react with peroxy radicals and hydroperoxides, thus stabilising industrial lubricants and engine oils. Syntheses and generalised chemical structures are as in Reactions (4.67. 69) [64, 72, 73] ... 

As it was mentioned above, polypropylenes are more prone to oxidation, hence, requiring significantly higher amounts of antioxidants and UV stabilizers compared to PE. It was shown that oxygen intake is much faster in polypropylene compared to that in PE [10], The primary reason is in the microbranched chemical structure of PP (see above), containing tertiary hydrogens that makes formation of hydroperoxides in PP much easier compared to that in polyethylenes. Overall, the mechanisms of oxidation (both photo- and thermooxidation) in PP and PE are quite different. For example, the termination reaction rates for oxidation in PE are 100-1000 times faster compared to PP [11]. 

Free radical formation is associated with the normal natural metabolism of aerobic cells. The oxygen consumption inherent to cell growth leads to the generation of a series of free radicals. The interaction of these species with molecules of a lipid nature produces new species such as hydroperoxides and different kinds of peroxides [135, 136], This group of radicals (superoxide, hydroxyl, and lipoid peroxides) may interact with biological systems in a cytotoxic manner. In this respect, it has been shown to posses an important antioxidant activity towards these radicals, which is mainly based on the properties of the hydroxyphenolic groups and the structural relations between the different parts of the chemical structure. Together with an ability to capture electrons, these... 

HA catabolism/degradation results in the formation of different HA fragments. The parental biopolymer and the enzyme-mediated HA fragments, regardless of chain length, have both identical chemical structure whereas fragmented chains produced under oxidative stress contain e.g. aldehyde-, hydroperoxide-, and other chemical groups [17]. 

HALS hardly absorb UV light but act most likely as radical scavengers and hydroperoxide decomposers. Chemical structures are mainly based on piperidines. Sterically hindered piperazines are known as well (Fig. 11.15). Secondary amines are the most common structures, but alkyl-amines or, more recently, alkoxyamines are commercially... 

Kinetics of the aralkyl hydroperoxides decomposition in the presence of tetraethylammonium bromide (Et NBr) has been investigated. Et NBr has been shown to reveal the catalytic properties in this reaction. The use of Et- NBr leads to the decrease up to 40 kJmol of the hydroperoxides decomposition activation energy. The complex formation between hydroperoxides and Et NBr has been shown by the kinetic and H NMR spectroscopy methods. Thermod5aiamic parameters of the complex formation and kinetic parameters of complex-bonded hydroperoxides have been estimated. The model of the reactive hydroperoxide - catalyst complex structure has been proposed. Complex formation is accompanied with hydroperoxide chemical activation. 

The numerous schemes suggested for this type of hydroperoxide decomposition are not always well substantiated. The chemical structure of polyalkene, as well as the process conditions (presence of admixtures, additives, temperature) play a decisive part in realising one or other mechanisms of hydroperoxide decomposition. 

Fig. 12.14. Competing cis abstraction and trans abstraction transition structures for hydroperoxide formation 2-methyl-2-butene. Adapted J. Am. Chem. Soc., 125, 1319 (2003), by permission of the American Chemical Society.

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