Hydrogen peroxide formation photochemical production

The transformation of isoquinoline has been studied both under photochemical conditions with hydrogen peroxide, and in the dark with hydroxyl radicals (Beitz et al. 1998). The former resulted in fission of the pyridine ring with the formation of phthalic dialdehyde and phthalimide, whereas the major product from the latter reaction involved oxidation of the benzene ring with formation of the isoquinoline-5,8-quinone and a hydroxylated quinone. 

The products of the photochemical reaction of oxygen and hydrogen in a flow system are ozone, hydrogen peroxide, and water. Mechanisms for the formation of these products are discussed below. 

Siefert et al. [136] simulated the chemical conditions of cloudwater using ambient aerosol samples suspended in an aqueous solution. Electron donors that are known to exist in atmospheric cloudwater (oxalate, formate, and acetate) were then added to the simulated cloudwater, and the solution irradiated with UV fight at A, > 300 nm. In all cases, H2O2 and Fe(II)aq were produced as a function of irradiation time. In addition, H2O2 was also produced without added electron donors simply using ambient aerosols collected from four different sites around the US. In addition, the production of Fe(II)aq showed that Fe from the ambient aerosol was available for photochemical redox reactions. In addition, the simultaneous release of Fe(II) and hydrogen peroxide will result in the indirect photochemical production of hydroxyl radical as follows ... 

Cuprous ions (Cu+) also react with hydrogen peroxide to make hydroxyl radicals (Halliwell and Gutteridge, 1985). The presence of iron salts and cuprous ions in the formulation can lead to an accelerated photochemical degradation of the drug by these reaction mechanisms. Metal ions can also participate in redox reactions with the drug or excipients in the preparation, depending on the redox properties of the species involved. Such reactions may further influence photochemical stability of the product, e.g., by the formation of photosensitizers. 

Oxidation of dithiomalonamides with hydrogen peroxide in the presence of hydrochloric acid leads to 3,5-diamino-4-chloro-l,2-dithiolium chlorides (20). The formation and deacetylation (or debenzoylation) of 3,5-diaryl-4-acyloxy-l,2-dithiolium salts have been described, and an earlier investigation of the mass spectra of the thermolysis products of dithiolium salts has been extended to include 3-alkylthio- and 3-arylthio-derivatives. Studies on the photochemical formation of 1,2-dithiolyl radicals and dithioketonate anions from dithiolium salts have been continued. ... 

The first step in the peroxide-induced reaction is the decomposition of the peroxide to form a free radical. The oxygen-induced reaction may involve the intermediate formation of a peroxide or a free radical olefin-oxygen addition product. (In the case of thermal and photochemical reactions, the free radical may be formed by the opening up of the double bond or, more probably, by dissociation of a carbon-hydrogen bond in metal alkyl-induced reactions, decomposition of the metal alkyl yields alkyl radicals.)... 

Photolysis of 3-buten-l-ol nitrite affords no cyclized products (Cy5/Cy4) neither does 5-hexen-l-ol nitrite (Cy6/Cy7). The same result is obtained on peroxydisulphate oxidation of 5-hexen-l-ol. In the Cy6/Cy7 case an important competitive pathway is probably 1,5-intramolecular ally lie hydrogen abstraction and, indeed, esr spin trapping by nitrosodurene " provides evidence of this. Cyclization in the Cy6/Cy7 case was considered to explain the reaction products of tetrahalogeno-o-benzoquinones with 2,3-dimethylbut-2-ene but was discarded in favor of a direct cycloaddition process on the basis of spin trapping and deuteration experiments. As discussed before, cyclization in the Cy3/Cy4 case must be difficult to observe because of the high j5-scission rate of oxyranylalkyl radicals. Nevertheless, this pathway has been used recently to explain the formation of diepoxides in the thermal-, photochemical-, or ferrous-salt-induced decomposition of unsaturated cyclic peroxides. In view of the multistep scheme involved this conclusion must await further confirmation. 

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