Peroxides, photolysis

The trans isomer is more reactive than the cis isomer ia 1,2-addition reactions (5). The cis and trans isomers also undergo ben2yne, C H, cycloaddition (6). The isomers dimerize to tetrachlorobutene ia the presence of organic peroxides. Photolysis of each isomer produces a different excited state (7,8). Oxidation of 1,2-dichloroethylene ia the presence of a free-radical iaitiator or concentrated sulfuric acid produces the corresponding epoxide [60336-63-2] which then rearranges to form chloroacetyl chloride [79-04-9] (9). 

Goi A, Trapido M (2002) Hydrogen peroxide photolysis, Fenton reagent and photo-Fenton for the degradation of nitrophenols a comparative study. Chemosphere 46 913-922... 

The application of the UV process alone showed low efficiency, which was attributed to the presence of UV-absorbing material. In addition, the photolysis of fluorene compared with the two other PAHs was significantly retarded when the fluorene was present in surface waters however, the oxidation rates of the three PAHs were essentially independent of the water type. It was concluded that the elimination of PAHs is mainly due to HO generated from hydrogen peroxide photolysis. In order to simplify the kinetic treatment, the pseudo first-order kinetics is used to determine the... 

The numerator of Equation (7.64) represents the production rate of hydroxyl radicals by hydrogen peroxide photolysis. When several UV absorbers are present, the fraction of radiation absorbed by peroxide to produce the hydroxyl radicals will be smaller. The denominator of Equation (7.64) represents the consumption rate of hydroxyl radicals by key scavengers. The value of /M and fPER denotes the relative importance of the destruction... 

Yu X-Y, Barker JR (2003) Hydrogen peroxide photolysis in acidic solutions containing chloride ions. 

Wardman P (1991) The reduction potential of benzyl viologen an important reference compound for oxidant/radical redox couples. Free Radical Res Comnun 14 57-67 Weeks JL, Rabani J (1966) The pulse radiolysis of deaerated aqueous carbonate solutions. I. Transient optical spectrum and mechanism. II. pKfor OH radicals. J Phys Chem 70 2100-2105 Yu X-Y, Barker JR (2003) Flydrogen peroxide photolysis in acidic solutions containing chloride ions. 

Einschlag FG, Feliz MR, Capparelli AL (1997) Effect of Temperature on Hydrogen Peroxide Photolysis in Aqueous Solutions, J. Photochem. Photobiol. A Chem. 110 235-242. 

The original interpretation of these results was in terms of crosslinking caused by radicals produced by peroxide photolysis (41). It was subsequently shown that a more likely mechanism is polymerization of residual monomer (39). Irradiation failed to insolubilize the polymer, which should have happened even if only a small amount of crosslinking had occurred. The residual monomer theory is also consistent with the irreproducibility of the process, which is a severe inconvenience. 

It is now realized that OH and RO radicals in liquid solution have an extremely short relaxation time due to various strong perturbations of the ir-levels (129). Their spectra are therefore too broad for detection, and this fact should be kept in mind when analyzing a complex ESR spectrum produced by the peroxide photolysis technique. Liquid photolysis of organic amines and hydrazines and the reaction of NC>2 with liquid olefins are known to produce nitrogen radicals. However, there is often a... 

For any specific type of initiation (i.e., radical, cationic, or anionic) the copolymer composition equation is independent of many reaction parameters. Since no rate constants appear as such in the copolymer equation, the copolymer composition is independent of differences in the rates of initiation and termination or of the presence or absence of inhibitors or chain transfer agents. Thus the same copolymer composition is obtained irrespective of whether initiation occurs by the thermal homolysis of initiators (such as AIBN or peroxides), photolysis, radiolysis, or redox systems. Under a wide range of conditions the copolymer composition is also independent of the degree of polymerization. The limitation on the above generalization is that the copolymer be of high molecular weight. It may be recalled that the derivation of Eq. (7.11) involved an assumption that the kinetic chains... 

The present discussion is by no means exhaustive. It is designed to provide a summary of the most significant and reliable kinetic data, at least those that appear so to the author. There is a variety of methods for producing alkyl radicals, and, naturally, there will be certain restrictions on experimental conditions depending on the method chosen. Some of the common methods for generation of methyl radicals, for example, include photolysis of acetone, pyrolysis of di-ferf-butyl peroxide, photolysis of biacetyl, photolysis of azomethane and decarbonylation of acetaldehyde. In the majority of cases discussed here, the reactions were followed by product determinations, employing gas chromatography. 

In addition to the photolytic ozonation experiments described above, hydrogen peroxide photolysis experiments were performed in the presence and absence of hydroxyl radical scavengers. These experiments were run using distilled water (a) as it came from the lab reservoir, (b) after oxygenation, and (c) after sparging with nitrogen to remove oxygen. The results are shown in Table I, in the form of the observed rate constants. 

Table I. Observed Hydrogen Peroxide Photolysis Rate Constants...

Replacement of acetic acid by another hydroxyl radical scavenger, bicarbonate, resulted in no accumulation of peroxide (Figure O, seemingly supporting Case II. Yet the stoichiometry of the peroxide photolysis experiments (Table I) suggests that the scavenging product, carbonate radical anion (Equation 11),... 

The gas chromatogram of the products formed in polystyrene peroxide photolysis is shown in Figure 6.5. The GC peaks 1, 3, 4 and 6 are attributed to the products formaldehyde, benzaldehyde, a-hydroxy acetophenone and phenyl glycol, respectively, and were identified by their characteristic MS [44, 45]. The MS of two of the photodecomposition products (GC peaks 4 and 7 due, to a-methoxy acetophenone and a-benzoyloxy acetophenone), respectively, are given in Figure 6.6. 

Figure 6.5 GC of the products formed in polystyrene peroxide photolysis in chloroform. Reproduced with permission from K. Subramanian, European Polymer Journal, 2002, 38, 1167. 2002, Elsevier [43]...

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