Hydrogen peroxide decomposition quantum yield

Quantum Yield of Ozone and Hydrogen Peroxide Decomposition at 2537 A. 

The formation of halohydrins can be promoted by peroxidase catalysts.465 Recently 466 it has been shown that photocatalysis reactions of hydrogen peroxide decomposition in the presence of titanium tetrachloride can produce halohydrins. The workers believe that titanium(IV) peroxide complexes are formed in situ, which act as the photocatalysts for hydrogen peroxide degradation and for the synthesis of the chlorohydrins from the olefins. The kinetics of chlorohydrin formation were studied, along with oxygen formation. The quantum yield was found to be dependent upon the olefin concentration. The mechanism is believed to involve short-lived di- or poly-meric titanium(IV) complexes. 

In this connection it is important to recall the dependency of the degradation rate of hydrogen peroxide, r(-H202), on the absorbed photon flow Op (Gmelin, 1966). In addition, the quantum yield of H2O2 photolysis is a discrete function of Op (Lunak and Sedlak, 1992, Gmelin, 1966). It was demonstrated that the rate of hydrogen peroxide decomposition at low incident photon flows (Op <10 photons s ) can be described by Eq. 6-11 and at Op above this value Eq. 6-12 is valid. 

Weeks JL, Metheson MS (1956) The Primary Quantum Yield of Hydrogen Peroxide Decomposition, J. Am. Chem. Soc. 78 ... 

We have recently described a calibration procedure for the determination of excitation quantum yields on commercial fluorimeters, utilizing the luminol standard , and have thereby determined singlet excitation quantum yields for the peroxyoxalate reaction with bis(2,4,6-trichlorophenyl) oxalate (TCPO), hydrogen peroxide and imidazole, using various activators . The same calibration method has been utilized to determine the singlet quantum yields obtained in the induced decomposition of protected phenoxyl-substituted 1,2-dioxetanes 6 and and compared them to the well-investigated... 

The careful studies of Chen and Taylor (22) on the photolysis at about 1650 A. have established the dependence of products on the experimental conditions. In static systems, hydrogen peroxide was not found, and the decomposition products were hydrogen and oxygen in a mole ratio of 2 1. The quantum yield under these conditions was about 0.01. In a flow system, hydrogen peroxide could be collected in a liquid nitrogen trap past the illumination zone, and evidence was obtained that it was not formed in the gas phase but in the trap itself. Under these conditions quantum yields as high as 0.3 were obtained, based on the sum of H2 and H2O2 formed. 

The absence of hydrogen peroxide in photolysis in static systems and the low-quantum yield of water decomposition may be explained by vari-... 

In static systems hydrogen and mercuric oxide were found as decomposition products (59,73). Hydrogen peroxide formation was not investigated. The quantum yield for a water vapor pressure of 8.5 mm. varied from 0.02 at 45°C. to 0.04 at 580°C. (59). In flow systems about 27% oxygen was found in the gaseous products, but no hydrogen peroxide was found (9). The flow system results have been substantiated in a more recent study (7) in which the quantum yields were found to be comparable to those obtained in static systems (59). 

According to the definition of quantum yield and the Beer-Lambert law, the overall decomposition rate of H202 in pure water, where hydrogen peroxide is the only absorber, can be described as follows ... 

Example 3-7 Calculate the amount of hydrogen peroxide that is theoretically decomposed by irradiation of its aqueous solution (V=l m ) within 1 h by a 10 kW medium-pressure mercury lamp that has a radiant power of 682 W at an active average wavelength X= (248 +253.7+ 265)/3 of 256 nm. The quantum yield of H2O2 decomposition equals 0.5 at 253.7 nm (Bolton and Cater, 1994). 

Some radical initiators decomposing by heat can also be decomposed by UV radiation. Photopolymerization of acrylonitrile in the presence of AIBN or hydrogen peroxide, or of other initiators [75-78] has been reported. The quantum yield of AIBN decomposition is 0.4 at 298 K and 0.6 at 318 K. Photopolymerization of methyl methacrylate, styrene, and vinyl acetate can be initiated by tetramethylsilane, methylchlorosilanes, and halides of Group IV metals [79]. We assume that the radicals are formed by homolytic splitting of the covalent bond... 

J.P. Hunt, H. Taube (1952). The photochemical decomposition of hydrogen peroxide. Quantum yields, tracer and fractionation effects. Nature, 74, 5999-6002. 

That an intermediate with a lifetime of some minutes (in the absence of a fluorescer) plays a key role in oxalate chemiluminescence was demonstrated by delayed fluorescer addition. Even when the fluorescer was added 70 minutes after the preparation of oxalate/hydroperoxide mixture, 53% of the quantum yield obtained by initial addition of the fluorescer was observed. On the other hand, the fluorescer evidently acts as catalyst in the chemiluminescent decomposition of that intermediate [2]. This intermediate could be transported by an inert gas stream from the oxalate/hydrogen peroxide mixture into a fluorescer solution, producing the fluorescence of the latter. In this case no consumption of the fluorescer took place. A charge-transfer complex between the fluorescer and the intermediate was proposed as early as 1967. The intermediate, as was mentioned above was assumed to be dioxetanedione (4) but it was not possible to identify it [2]. 

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