Photooxidative decomposition

Isopropyl-4,5,6-fm-butylpyridazine, which exists in the twist conformation, is transformed upon photolysis into the corresponding 1,2-Dewar-pyridazine, which is stable (91AG1495). Irradiation of the ketone 179 with UV light produces about 10% of 180 (92JA1838). Photooxidative decomposition of 3,3,6,6-tetraalkyl-substituted perhydropyridazines was investigated and it was found that decomposition is stereospecific and that the 1,4-biradical determined the stereochemical outcome and not the 1,4-cation radical. Cyclobutane and 1-butene derivatives were products identified (93JA4925). 

The online photooxidative decomposition of phosphoms compounds to orthophosphate has also been applied to the determination of dissolved organic phosphoms (DOP) and TP in soil extracts and leachates, mnoff waters, natural, and wastewaters. For instance, the MPFS depicted in Figure 7.33 allows the spectrophotometric determination of dissolved orthophosphate and DOP in wastewater samples [106]. The determination of orthophosphate is based on the vanadomolybdate method. Inline ultraviolet photooxidation is employed to mineralize organic phosphoms to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow toward the UV lamp to carry out the determination of organic phosphoms. 

Another way to induce visible-light photocatalytic activity is the chemical bonding of carboxyl groups onto the SrTiOs surface during the microwave-assisted solvothermal synthesis in KOH methanol-oleic acid solutions [30]. This behavior was assigned to a dipole layer that induced an attracting potential for electrons inside the SrTiOs nanoparticles. The photocatalysts were tested in the photooxidative decomposition of NO [31]. 

Thermal, Thermooxidative, and Photooxidative Degradation. Polymers of a-olefins have at least one tertiary C-H bond in each monomer unit of polymer chains. As a result, these polymers are susceptible to both thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups. For example, thermal decomposition of... 

Secondly, the interaction of hindered amines with hydroperoxides was examined. At room temperature, using different monofunctional model hydroperoxides, a direct hydroperoxide decomposition by TMP derivatives was not seen. On the other hand, a marked inhibitory effect of certain hindered amines on the formation of hydroperoxides in the induced photooxidation of hydrocarbons was observed. Additional spectroscopic and analytical evidence is given for complex formation between TMP derivatives and tert.-butyl hydroperoxide. From these results, a possible mechanism for the reaction between hindered amines and the oxidizing species was proposed. 

Separate experiments in which tert.-butoxy radicals were produced thermally in benzene from di-tert.-butyl peroxyoxalate failed to reveal any direct reaction of these radicals with amine II. Even at higher temperatures (A/ 150°C, dichlorobenzene, +00+ decomposition), the +0 radicals attacked neither amine II nor nitroxide I. The earlier described experiments of ketone photooxidation showed additionally that amine II displays no specially marked reactivity towards peroxy radicals. 

The fluorescence lifetime was determined to be 1124ps for 35a, 785 ps for 35b, and 831 ps for 43 in dichloromethane, whereas in the corresponding amorphous films a nonexponential decay with shorter time constants was observed [118, 119]. These lifetimes are similar to the parent oligophenyls but different from fluorene (10 ns) [120, 121]. When applying oligophenyls as luminescent films, however, we must consider that photooxidation may occur if molecular oxygen is present [122, 123], The proposed pathway for the decomposition is... 

Here pn is 1,2-diaminopropane and bn is 2,3-diaminobutane. Decomposition of the amine cation radicals obtained by photooxidation of the ligands en, bn, and pn have been discussed by Moeller. The products of Co(en)33+ photolysis can be satisfactorily explained by postulating that carbon-carbon bondbreaking is the principal step in decomposition of the cation radical H2NCH2CH2NH2t.58 Presuming a similar mechanism to obtain in photoreduction of Co(pn)33+, there are then two possible reaction pathways leading to different products. 

It has been shown that the benzophenone sensitized decomposition of benzoyl peroxide is due in part to formation of the benzophenone ketyl radical, which induces decomposition.98,99 Hydrocarbon sensitized peroxide decomposition is discussed in Section IV.A.4. The formation of benzonitrile from the benzophenone sensitized irradiation of benzalazine, which was originally attributed to hydrogen abstraction by benzophenone,100 actually results from a photooxidation.101... 

Thermal decomposition of the photooxides 113 (R = Me, Ph) may result in the formation of benzo[c]furans (114) both compounds were trapped as Diels-Alder adducts (115, R = Me, Ph). It was possible, however, to prepare 114 (R = Ph) by another route (Section IV,A,5). 

When the photooxide of 9-phenylanthracene (113, R = Ph) is treated with aqueous acetic acid, 3-(o-hydroxyphenyl)-l-phenylbenzo[c]furan (114, R = Ph) is obtained in 22% yield. The mechanism of Scheme 6 has been given for this rearrangement. Thermal decomposition of 113(R = Me, Ph), which might occur as shown in Scheme 7, also gives 114 (R = Me, Ph) in these cases the benzo[c]furans have not been isolated. They could be trapped, however, with A-methylmaleimide. ... 

A number of reports of photochemical decomposition of heteroaromatic compounds have appeared in the literature during the past 50 or 60 years. A few of these undoubtedly involve photooxidative processes, whereas others have been examined in the vapor phase, often at elevated temperatures. Recent work includes the study of the photodecomposition of thiophene128 andpyrazine.129 Furans undergo... 

N-type semiconductors can be used as photoanodes in electrochemical cells Q., 2, 3), but photoanodic decomposition of the photoelectrode often competes with the desired anodic process (1 4 5). When photoanodic decomposition of the electrode does compete, the utility of the photoelectrochemical device is limited by the photoelectrode decomposition. In a number of instances redox additives, A, have proven to be photooxidized at n-type semiconductors with essentially 100% current efficiency (1, 2, 3, 6>, ], 8, 9). Research in this laboratory has shown that immobilization of A onto the photoanode surface may be an approach to stabilization of the photoanode when the desired chemistry is photooxidation of a solution species B, where oxidation of B is not able to directly compete with the anodic decomposition of the "naked" (non-derivatized) photoanode (10, 11, 12). Photoanodes derivatized with a redox reagent A can effect oxidation of solution species B according to the sequence represented by equations (1) - (3) (10-15). 

By exciting the red-orange cyclooctatetraene dianion 1 in the presence of cyclooctatetraene in our photoelectrochemical cell (n-TiC>2/NH3/Pt), we were able to observe photocurrents without detectable decomposition of the anionic absorber (2). Presumably, a rapid dismutation of the photooxidized product inhibited electron recombination, producing a stable hydrocarbon whose cathodic reduction at the counter electrode regenerates the original mixture essentially quantitatively (eqn 3). 

In addition to the thermal decomposition the photochemical reaction of geminal diazide 62 was also studied. Irradiation of an acetone solution of 62 under an inert gas atmosphere afforded a complex mixture of products which could not be separated or identified. However, if the reaction was carried out in the presence of oxygen the uracil derivative 66 was obtained in 48 % yield. Surprisingly, in addition to the oxidation of the CH2 group, the 6-diazidomethyl function was completely lost during the reation [91JCS(P1)1342]. At the present time no mechanistic explanation for this unusual behavior can be presented. On the other hand, photooxidation of compound 63 leads straightforward to compound 67 [91 JCS(P1)1342],... 

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