Photochemical oxidation potential

Physical Properties. Tetrahydrofurfuryl alcohol (2-tetrahydrofuranmethanol) [97-99-4] (20) is a colorless, high-boiling liquid with a mild, pleasant odor. It is completely miscible with water and common organic solvents. Tetrahydrofurfuryl alcohol is an excellent solvent, moderately hydrogen-bonded, essentially nontoxic, biodegradable, and has a low photochemical oxidation potential. Most appHcations make use of its high solvency. The more important physical properties of tetrahydrofurfuryl alcohol are Hsted in Table 1. 

Photochemical Oxidants Creation Potential. This is a measure of the potential to generate smog and is expressed relative to ethene. 

Research on photochemical oxidants, including o ne, was confined primarily to California during the 19S0 s. By 1959, ozone was known to be an important pollutant in the eastern United States and southern Canada. It is now known as a ubiquitous pollutant and has been widely studied throughout the United States and Canada. By 1972, several other countries had recognized the potential effects of photochemical oxidants on v etation and initiated research. 

Enhanced susceptibility to respiratory exposure to infectious agents is of considerable potential public-health significance. This has been reported to occur in mice exposed to ozone at as low as 0.08 ppm, the lowest reported effect concentration in laboratory animal studies. It seems essential, therefore, to continue and expand research on the effect of ozone and other photochemical oxidants on physiologic protective mechanisms of the lung. Appropriate dose-response studies should be included to confirm or establish the exposure concentration-time relationships that result in increased susceptibility to inhaled microorganisms, and studies of the cellular responses and mechanisms should be conducted with a view to providing methods that are applicable to epidemi-ol( c studies in oxidant-exposed human populations. 

Scheme 8.8. Reaction sequence for the photochemical generation of a-atninoalltyl radicals and determination of oxidation potential, ref. [78J.

Methylquinolinium ion derivatives are reduced regioselectively to 1,4-dihydroqui-nones by (TMS SiH under photochemical conditions42. Mechanistic studies demonstrated that the reactions are initiated by photoinduced electron transfer from silane to the singlet excited states of 1-methylquinolinium ion derivatives to give the silane radical cation—quinolinyl radical pairs, followed by hydrogen transfer in the cage to yield 1,4-dihydroquinones and silicenium ion. The one-electron oxidation potential of (TMS SiH is 1.30 V42. 

Similar results were obtained [139] with the three dimethoxybenzenes and acrylonitrile, methacrylonitrile, and crotonitrile. The amounts of substitution products decrease in the order acrylonitrile (49%) > methacrylonitrile (45%) > crotonitrile (6%), which agrees with the electron affinities of these compounds. Simultaneously, the amount of addition product increases acrylonitrile, 0% methacrylonitrile, 38% crotonitrile, 67%. In the series of anisole and the dimethoxybenzenes with crotonitrile, the amount of substitution products decrease in the order ortho- and para-dim ethoxy benzene > meta-dimethoxyben-zene > anisole, which is just the reverse of the order of their oxidation potentials. Ohashi et al. [139] have attempted to relate the photochemical behavior of these systems to the free enthalpy of electron transfer in the excited state as calculated with the Rehm-Weller equation, AG = E(D/D+) - E(A /A) - el/eR - AE00. 

Photochemical oxidation or smog formation potential (PCOP). 

The generation of cr-radical cations from saturated hydrocarbons requires very strong SET oxidizers. The oxidation reactions can be accomplished by chemical electron transfer (CET), photochemical electron transfer (PET), and anodic oxidation. The oxidation potentials of stable, organic CET oxidants, e.g., commercially available tris(4-bromophenyl)aminium hexachloroantimonate (TBA +SbCI<,) or tris(2,4-dibromo-phenyl)aminium hexachloroantimonate (TDA +SbCl6 ), are too low (1.06 and 1.50 V... 

Table VI. Quantum yields (0) for photochemical oxidation under aerobic conditions at pH 7, and oxidation peak potentials (E ) for electrochemical oxidation at pH 7.3, of the dihydrodimers D D,. shown in Scheme 21.

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