Hydroperoxide photolysis, quantum yields

This quantum yield corresponds to the overall process where hydrogen peroxide is not just removed by reaction (54), its direct photolysis, but also by parallel reactions involving the hydroxyl and hydroperoxide radicals as shown below ... 

Table I shows the quantum yields for photolysis of tert-butyl hydroperoxide in hexane at 36°C (6). It is evident that the quantum yield for photolysis is greater than unity, which is typical for a radical-chain process, and depends on the hydroperoxide concentration, ranging from 3.5 at 1% hydroperoxide to 10 at 5%. Similar results are shown in...

Table I. Quantum Yields for Photolysis of tert-Butyl Hydroperoxide in Hexane, 36°C, A = 313 nm...

Figure 3. Photolysis of cis-polyisoprene hydroperoxide (0.06% -00H) in 1,2-dichloroethane at 30°C determination of quantum yields at various wavelengths...

Table V. Apparent Quantum Yields for tert-Butyl Hydroperoxide Photolysis in the Presence of Methyl tert-Butyl Ketone 0.31M Hydroperoxide in Hexane at 36°C, A — 322 nm...

The macroradical formed to reaction (16) interacts with oxygen, leading to a normal chain reaction and the formation of hydroperoxides. Accordii to the data of [85], the quantum yield of carbonyl groups in the photolysis of polyethylene is no greater than 0.1. This means that the kinetic chains in photooxidation are not very long. In view of this, termination of the chains by means of antioxidants is hindered in practice, since in the case of short chains and a high rate of initiation, effective inhibition is impossible. The formation of unsaturated compoimds during photolysis [reactions (15) and (16)] facilitates further oxidation of the polyolefin. 

The photolysis frequencies of photodissociation of H2O2 were calculated as a function of solar zenith angle for clear-sky conditions and an overhead ozone column of 350 DU, assuming the process (I) occurs with a quantum yield of unity. These data are presented in figure IX-K-2 where they can be compared with y-values for some alkyl hydroperoxides. 

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