Hydrogen Peroxide and Hydroperoxides

Light-induced homolysis of some organochromium complexes produces low concentrations of Cr used to study the reaction of Cr and H202. The first and rate-determining step of the reaction shown in equation (32), 

The formation of intensely colored CrR complexes yields kct = (7.06 0.04) X lO M s (25°C). Identical results were obtained by the stopped-flow technique under different conditions. 

The rate constant for the reaction of [Cu(phen)2] with H202,  

The oxidation of Cu(I) with H2O2 in aqueous HCl shows second-order kinetics, but with a complicated dependence on CF, consistent with the presence of different copper(I)-Cr species in solution. The kinetics of H2O2 oxidation of U(IV) in aqueous HCl, 

Diethylenetriaminepentaacetatocobalt(II), [Co(dtpa)] , reacts with H2O2 with an approximate 2 1 stoichiometry, yielding [Co(dtpa)] at pH 5, and a mixture of [Co(dtpa)] and a -peroxo dimer at pH 5. 

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The application of CPO, HRP and CiP is limited to sterically unencumbered substrates and all these peroxidases produce the same absolute configuration of the chiral hydroperoxide. To overcome this limitation, the semisynthetic enzyme selenosubtilisin, a mimic for glutathione peroxidase, with the peptide framework of the serine protease subtilisin was developed by Bell and Hilvert. This semisynthetic peroxidase catalyzes the reduction of hydrogen peroxide and hydroperoxides in the presence of 5-mercapto-2-nitrobenzoic acid. It was utilized by Adam and coworkers and Schreier and coworkers for the kinetic resolution of racemic hydroperoxides (equation 17) . The results obtained were very promising. 

Traylor TG, Ciccone JP (1989) Mechanism of reactions of hydrogen peroxide and hydroperoxides with iron(III) porphyrins. Effects of hydroperoxide structure on kinetics. J Am Chem Soc 111 8413-8420... 

Traylor TG, Xu F (1990) Mechanisms of reactions of iron(III) porphyrins with hydrogen peroxide and hydroperoxides solvent and solvent isotope effects. J Am Chem Soc 112 178-186... 

The detrimental effect could also be explained by the fact that hydrogen peroxide and hydroperoxides are produced by the oxidation of phenols, lignin and xylan. These peroxides easily decompose in the presence of metals like cobalt and iron, producing radicals like OH and H02 which are certainly very reactive (23). 

Radical production from peroxidase-like systems, for example from the peroxide-supported oxidation of amino compounds catalyzed by protohemin and metmyo-globin, has received attention [174]. Both hydrogen peroxide and hydroperoxides (e.g., r-butyl hydroperoxide and cumene hydroperoxide) can be effective sources of oxidizing equivalents for these reactions. Since the enzyme prostaglandin synthase contains both cyclooxygenase and hydroperoxidase activities, either a substrate for the cyclooxygenase or an added hydroperoxide will support the catalyzed oxidation of substrates [175]. 

The mechanisms of the reactions of hydrogen peroxide and hydroperoxide with iron(III) porphyrins have been investigated. The reactions with t-butyl hydroperoxide and pentafluoroiodosylbenzene in CH2Cl2(Me0H/H20), shown in equations (8) and (9), yield the iron- oxene center, which in turn may act as an... 

Organic hydroperoxides can be prepared by Hquid-phase oxidation of selected hydrocarbons in relatively high yield. Several cycHc processes for hydrogen peroxide manufacture from hydroperoxides have been patented (84,85), and others (86—88) describe the reaction of tert-huty hydroperoxide with sulfuric acid to obtain hydrogen peroxide and coproduct tert-huty alcohol or tert-huty peroxide. 

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45). 

Most likely singlet oxygen is also responsible for the red chemiluminescence observed in the reaction of pyrogaHol with formaldehyde and hydrogen peroxide in aqueous alkaU (152). It is also involved in chemiluminescence from the decomposition of secondary dialkyl peroxides and hydroperoxides (153), although triplet carbonyl products appear to be the emitting species (132). 

In the preparation of hydroperoxides from hydrogen peroxide, dialkyl peroxides usually form as by-products from the alkylation of the hydroperoxide in the reaction mixture. The reactivity of the substrate (olefin or RX) with hydrogen peroxide is the principal restriction in the process. If elevated temperatures or strongly acidic or strongly basic conditions are required, extensive decomposition of the hydrogen peroxide and the hydroperoxide can occur. 

Organomineral hydroperoxides have been prepared from hydrogen peroxide and organomineral haUdes, hydroxides, oxides, peroxides, and amines (10,33). If HX is an acid, ammonia is used to prevent acidic decomposition. 

Synthesis. Dialkyl peroxides are prepared by the reaction of various substrates with hydrogen peroxide, hydroperoxides, or oxygen (69). They also have been obtained from reactions with other organic peroxides. For example, dialkyl peroxides have been prepared by the reaction of hydrogen peroxide and alkyl hydroperoxides with alMating agents, eg, RX and olefins (33,66,97) (eqs. 24—27). 

The following commercially available dialkyl peroxides are produced according to equations 24—27 di-Z fZ-butyl peroxide from hydrogen peroxide and sulfated tert-huty alcohol or isobutylene dicumyl peroxide from a-cumyl hydroperoxide and cumyl alcohol, cumyl chloride, and/or a-methylstyrene m- and -di(2-/ f2 -butylperoxyisopropyl)ben2ene [2781-00-2] from tert-huty hydroperoxide [75-91-2] and m- and -di(2-hydroxyisopropyl)ben2ene ... 

Hydroxyalkyl hydroperoxides from cycHc ketones (1), where X = OH, R =, H and R, R = alkylene, apparentiy exist in solution as equihbrium mixtures of the cycHc ketone, hydrogen peroxide, and other peroxides, eg, the dihydroperoxide (1) in which X = OOH, and dialkyl peroxides (2) where X = OH and Y = OH or OOH. Due to the existence of this equihbrium, the latter two dialkyl peroxides react as mixtures of monomeric hydroperoxides in solution. 

Hydroxyalkyl hydroperoxides having at least one a-hydrogen ie, (7, X = OH, R = alkyll, R = R = H), ie, those derived from aldehydes, lose hydrogen peroxide and form dialkyl peroxides (2, X = Y = OH), especially in the presence of water ... 

Acidic hydrolysis of these hydroxyaLkyl hydroperoxides yields carboxyUc acids, whereas basic hydrolysis regenerates the parent aldehyde, hydrogen peroxide, and often other products. When derived from either aldehydes or cycHc ketones, peroxides (1, X = OH, = H, R, = alkylene or... 

Vinyl monomers may be polymerized at favorable rates in an aqueous medium containing an emulsifier and a water-soluble initiator. A typical simple Tecipe would consist of the following ingredients with their proportions indicated in parts by weight 100 of monomer, 180 of water, 2 to 5 of a fatty acid soap, and 0.1 to 0.5 of potassium persulfate. Cationic soaps (e.g., dodecylamine hydrochloride) may be used instead of the fatty acid soap, and various other initiators may replace the persulfate (e.g., hydrogen peroxide and ferrous ion, or a water-soluble organic hydroperoxide). 

Thiols are also important protection against lipid peroxidation. Glutathione (7-Glu-Cys-Gly) is used by several glutathione-dependent enzymes such as free-radical reductase (converts vitamin E radical to vitamin E), glutathione peroxidase (reduces hydrogen peroxide and lipid hydroperoxides to water and to the lipid alcohol, respectively), and others. In addition, the thiol group of many proteins is essential for function. Oxidation of the thiol of calcium ATPases impairs function and leads to increased intracellular calcium. Thiol derivatives such as the ovothiols (l-methyl-4-mercaptohistidines) (Shapiro, 1991) have been explored as therapeutics. 

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