Ethane formation, photochemistry

The photochemistry of Titan s atmosphere can be summarized as follows the unsaturated compounds are formed from HCN and C2H2, which is derived from CH4. Methane decomposition leads to further ethane formation. 

The location of the oxime group in the product in Scheme 4 depends upon where the methyl group is located, but the yields can be high (79%). Irradiation of 2-methoxyfuran also induces side-chain dissociation and the formation of lactones (i.e., methylbutenolides).21 Here the abundant formation of ethane testifies to the participation by methyl radicals. Such reactions are too complex for synthetic purposes. This is true also of 2-acetoxyfuran photochemistry in which the photo-Fries reaction is not observed.21 Curiously, furan itself sensitizes the photo-Fries reaction in benzenoid esters.22... 

Both neutral and charge-transfer photochemistry is involved in the photodissociation at 248 nm of methyl iodide as a monolayer (1 ML) or up to 10 ML on a silverfl 11) surface. Such reactivity involves the fission of the C—I bond and the formation of methyl radicals and iodide adsorbed at the surface12,13a. Dissociation also occurs during X-ray photoelectron spectroscopy136. Multilayers of methyl iodide on silverfl 11) surfaces undergo C—I bond fission on irradiation at 248 nm. Several products such as ethane, ethyl iodide and iodoform are formed but the principal reaction path, which is somewhat time-dependent, yields methane and methylene di-iodide14. 

These reaction products can be explained on the basis of the pathway shown in Scheme 8.4. This pathway involves an initial photoinduced one-electron transfer in a uranyl formate complex to give UO2 and a formate radical, followed by disproportionation to give and carbon dioxide. The photochemistry of the uranyl ion with either acetic acid or its higher homologues follows a similar type redox pathway. Such a pathway with acetic acid leads to the formation of carbon dioxide, ethane, and carbon dioxide ... 

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