Photolysis with hydrogen

UV absorbers (UVA) act by absorbing UV light hence retarding the photolysis of hydroperoxides. Their activity is also associated with hydrogen bonding between the 2-hydroxy group and the carbonyl chromo-phore [22]. Typical examples are based on 2-hydroxy-benzophenones and 2-hydroxybenztriazoIes (e.g., Table lb, AO 23 and AOs 24-26). 

Attempts to effect ring expansion of methyl 2-azidobenzoate in the presence of other nucleophiles have failed. Thus, photolysis in tetrahydrofuran solution saturated with hydrogen sulfide, or with ammonia, produced methyl 2-aminobenzoate in 54 and 37 % yield, respectively, as the sole identifiable product.197 Photolysis of phenyl azide in ethanolic phenol gave 2-phenoxy-3//-azepine in poor yield (8 %).203,204 2-Mesityl-3//-azepine (10 %) is the surprising, and only tentatively explained, product from the photolysis of phenyl azide in mcsitylene in the presence of trifluoroacetic acid.179... 

The results of this study are presented in Table 4.7. As can be seen from the data in Table 4.7, decarbonylation with hydrogen or deuterium transfer to the resulting radical is a relatively efficient process. The failure to observe this reaction using acetone or acetophenone as photosensitizer would suggest a singlet pathway for the direct photolysis of the aldehyde. In agreement, decarbonylation could not be quenched by naphthalene, piperylene, or 1,3-cyclohexadiene when the aldehyde was excited directly. The reaction could, however, be somewhat quenched by the addition of tri-n-butylstannane. The products in this case were... 

To our knowledge, the first published report of a photocatal-ytic reaction at elevated pressure was W. Strohmeyer1s hydrogenation of 1,3-cyclohexadiene under hydrogen at 10 atm /22/. On photolysis, the iridium complex 8 formed a very active catalyst, probably by dissociation of a phosphine ligand (Equation 17). At 70 C, with hydrogen at 10 atm, and a catalyst/substrate ratio of 1/100,000, the activity was 196 per minute and the turnover number was 96,000 mol of product/mol catalyst. 

Dilling, W.L., Gonsior, S.J., Boggs, G.U., Mendoza, C.G. (1988) Organic photochemistry. 20. A method for estimating gas-phase rate for reactions of hydroxyl radicals with organic compounds from their relative rates of reaction with hydrogen peroxide under photolysis in 1,1,2-trichlorotrifluoroethane solution. Environ. Sci. Technol. 22, 1447-1453. 

Hydrogen production process by direct photolysis of hydrogen-containing compounds may be based on different types of photosensitizers in parallel with inorganic semiconductors. The model systems for photoinduced hydrogen production with porphyrins and hydrogenase were developed [4],... 

Three types of photochemical reaction of carbohydrate acetals have been investigated. Early studies centered on the photochemical fragmentation of phenyl glycosides, and the photolysis of o-nitrobenzyli-dene acetals. (The latter reactions will be discussed with the photolysis of other nitro compounds see Sect. VII,1.) Later experiments were concerned with hydrogen-abstraction reactions from acetal carbon atoms by excited carbonyl compounds. 

Bonhoeffer and Farkas estimated k3/k2 100 and claimed that at 15 % decomposition the photolysis is completely self inhibited. More recent work by Ogg and Williams9,10 showed that for the photolysis with 2537 A radiation, k3/k2 is independent of HI pressure (50-150 torr), independent of temperature and has a value 3.5+0.3. The effect of cyclohexane as an inert diluent11 was to increase k3/k2 to 7.0+0.4 at 155°, which value remained constant at high cyclohexane hydrogen iodide ratios. This result was attributed to collisional thermalisation of the hot H atoms produced by 2537 A radiation and this limiting high-pressure value of k3/k2 = (k3/k2)aa was considered to be that for thermally equilibrated H atoms. 

The protonation rate constant of the triplet state of thionine has been measured as a function of temperature and hydrogen ion concentration using flash photolysis with a frequency-doubled neodynium laser 1614)... 

Peroxynitrite is an important cytotoxin that results in vivo from the direct reaction of superoxide and nitric oxide. There are several methods to synthesize peroxynitrite, including the solid-state photolysis of KNOs, the ozonation of sodium azide, or the alkaline reaction of nitrite esters with hydrogen peroxide. Perhaps the most common peroxynitrite synthesis involves treating an acidified solution of hydrogen peroxide with nitrite, followed by an immediate quench with base. Although this synthesis is facile, quick, and affordable, it results in... 

The furan (450) is also formed on photolysis of 1,3-diphenylindenone epoxide (449) in ethanol. Hydrolysis of the epoxide (449) in acetic acid with hydrogen chloride was also... 

Flash photolysis studies of mixtures of ozone and hydrogen (6,56) have shown that the reaction of 0(1D) atoms with hydrogen yields vibra-tionally excited OH radicals. Studies of ozone and hydrogen mixtures in the visible (35) and in the ultraviolet (94) have shown that water is formed and that the rate of ozone decomposition is increased in the presence of hydrogen. 

HCo(CN)5]3- gives hydrogen and [Co(CN)5]3 on photolysis with 313 nm radiation but photolysis of the product with 254 nm radiation regenerates [HCo(CN)5]3, probably with formation of cyanogen.68... 

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