Hydrocarbons, photooxidation

The acyl radicals formed in ketone photolysis are excited and, therefore, rapidly splits into CO and alkyl radical (in the gas phase). Since aldehydes and ketones are products of oxidation, continuous hydrocarbon photooxidation is an autoaccelerated process. 

FeA(CO)A(n-C5H5)A Inert In Hydrocarbon Photooxidation via CTTS in Halocarbon (65)... 

Besides the various other substances with toxic effects, polluted air may also contain aldehydes, which are formed as reaction products of hydrocarbon photooxidation. The reactions of aldehydes are not very rapid, so that they are accumulated in concentrations of about 0.2 ppm in the photochemical smog. Formaldehyde and acrolein are the most important compounds in this group. Their irritating nature obviously contributes to the increase of the smog smell and to its irritating effects on the eyes. According to estimates, formaldehyde represents a fraction of 50% out of all the aldehydes in the polluted air. Acrolein is more irritating than formaldehyde and forms about 5% of the aldehydes. 

Stern, J. E., Flagan, R. C.. Grosjean, D., and Seinfeld, J. H. (1987) Aerosol formation and growth in atmospheric aromatic hydrocarbon photooxidation. Environ. Sci. TechnoL, 21, 1224-1231. 

Fluorinated ether-containing dicarboxyhc acids have been prepared by direct fluorination of the corresponding hydrocarbon (17), photooxidation of tetrafluoroethylene, or by fluoride ion-cataly2ed reaction of a diacid fluoride such as oxalyl or tetrafluorosuccinyl fluorides with hexafluoropropylene oxide (46,47). Equation 8 shows the reaction of oxalyl fluoride with HEPO. A difunctional ether-containing acid fluoride derived from HEPO contains regular repeat units of perfluoroisopropoxy group and is terminated by two alpha-branched carboxylates. 

Figure 2. Typical photochemical smog cycle in which hydrocarbons HC are consumed, NO is photooxidized to N02, and O3 accumulates. A. Typical variables. B. Showing transformed variable [03-NO ]. Adapted from Moshiri (75).

The transformation of arenes in the troposphere has been discussed in detail (Arey 1998). Their destruction can be mediated by reaction with hydroxyl radicals, and from naphthalene a wide range of compounds is produced, including 1- and 2-naphthols, 2-formylcinnamaldehyde, phthalic anhydride, and with less certainty 1,4-naphthoquinone and 2,3-epoxynaphthoquinone. Both 1- and 2-nitronaphthalene were formed through the intervention of NO2 (Bunce et al. 1997). Attention has also been directed to the composition of secondary organic aerosols from the photooxidation of monocyclic aromatic hydrocarbons in the presence of NO (Eorstner et al. 1997) the main products from a range of alkylated aromatics were 2,5-furandione and the 3-methyl and 3-ethyl congeners. 

Tuazon EC, H MacLeod, R Atkinson, WPL Carter (1986) a dicarbonyl yields from the NOj.-air photooxidations of a series of aromatic hydrocarbons in air. Environ Sci Technol 20 383-387. 

An interesting, and slightly different, autoxidation is photooxidation of hydrocarbons such as 9,10-diphenylanthracene (102) in solvents such as CS2. The light absorbed converts the hydrocarbon into the stabilised diradical (103, cf. p. 337), or something rather like it,... 

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. 

Cope, V.W., Kalkwarf, D.R. (1987) Photooxidation of selected polycyclic aromatic hydrocarbons and pyrenequinones coated on glass surfaces. Environ. Sci. Technol. 21(7), 643-648. 

For detailed information and bibliography on photooxidation of hydrocarbons, see Chapter 3. 

The rate of photooxidation does not virtually depend on temperature. Therefore, photooxidation gives a possibility to oxidize the hydrocarbon at room or lower... 

To perform the dissociation of the hydrocarbon to alkyl radicals with C—C bond scission, a hydrocarbon molecule should absorb light with the wavelength 270-370 nm. However, alkanes do not absorb light with such wavelength. Therefore, photosensitizers are used for free radical initiation in hydrocarbons. Mercury vapor has been used as a sensitizer for the generation of free radicals in the oxidized hydrocarbon [206-212], Nalbandyan [212-214] was the first to study the photooxidation of methane, ethane, and propane using Hg vapor as photosensitizer. Hydroperoxide was isolated as the product of propane oxidation at room temperature. The quantum yield of hydroperoxide was found to be >2, that is, oxidation occurs with short chains. The following scheme of propane photoxidation was proposed [117] ... 

Polynuclear aromatic hydrocarbons can be oxidized photolytically with the formation of cyclic peroxide. For example, anthracene is photooxidized to peroxide with the quantum yield 0 = 1.0 [205], The introduction of quenchers lowers the peroxide yield. 

Dienic hydrocarbons are photooxidized to cyclic peroxides. For example, terpinene is photooxidized to ascaridole peroxide [217] ... 

Note that a native oxide film also forms under dry conditions in ambient air the oxidation rate of this process can be enhanced by ultraviolet (UV)-ozone photooxidation (Tal, Vil]. Oxide-covered Si surfaces exhibit low contact angles. Only if the oxide surface is contaminated, for example by a monolayer of absorbed hydrocarbons, may larger contact angles be observed. 

Glasson, W. A. Effect of carbon monoxide on atmospheric photooxidation of nitric oxide—hydrocarbon mixtures. Environ. Sci. Technol. 9 343-347, 1975. 

Glasson, W. A., and C. S. Tuesday. Hydrocarbon reactivity and the kinetics of the atmospheric photooxidation of nitric oxide. J. Air Pollut. Control Assoc. 20 239-243, 1970. 

Grimsrud, E. P., H. H. Westberg, and R. A. Rasmussen. Atmospheric reactivity of monoterpene hydrocarbons, NOs photooxidation and ozonolysis. Int. J. Chem. Kinet. Symp. 1 (Chemical Kinetics Data for the Lower and Upper Atmosphere) 183-195, 1975. 

From all available evidence, the hydroxyl radical plays a major role in the photooxidation and aerosol formation processes for aromatic hydrocarbons. However, much research remains to be done to improve our knowledge in this field. 

Schuck, E. A., and G. J. Doyle. Photooxidation of Hydrocarbons in Mixtures Containing Oxides of Nitrogen and Sulfor Dioxide. Report No. 29. San Marino, Calif. Air Pollution Foundation, 1959. 126 pp. 

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