Photolysis methane

We have reproduced the results reported in the literature for both methane photolysis and catalytic photolysis of water. In experiments that combine elements of both systems. 

As can be seen from Table 3.1, the Titanian atmosphere contains a relatively large amount of ethane. Laboratory results show that methyl radicals (H3C), which are primary products of methane photolysis, may be present in the upper reaches of the atmosphere ... 

The latter path is favored energetically and is quite similar to other known reactions, such as methane photolysis. Vacuum ultraviolet photolysis (1236 A.) of CH488 is believed to yield CH2 and H2 as the major primary process, although other primary steps occur to some extent. 

Methane, a. Molecular Elimination of Hydrogen. Because of analytical difficulties, the early work116117 on methane photolysis was of questionable significance with regard to the attempts to understand the mechanism of the photolysis. Recently, the primary process in methane photolysis has been elucidated by examining the isotopic... 

We now discuss the chemical fate of the other degassed compounds, such as CH4, CO2, and H2O in the first atmosphere (cf Table 2.7). Methane photolysis occurs at a-Lyman wavelength (121.6 nm) into H, H2, CH, CH2 and CH3 and, in the atmosphere of the Titan, it is thought to promote the propagation of hydrocarbon chemistry (Wilson and Atreya 2000). A small presence of O2 and OH radicals is a result of H2O photolysis. Assuming CH4 and H2O to represent first the degassing products, the formation of CO2 is an irreversible subsequent step. 

Wilson, E. H. and S. K. Atreya (2000) Sensitivity studies of methane photolysis and its impact on hydrocarbon chemistry in the atmosphere of Titan. Journal of Geophysical Research 105, 20263-20273... 

Sagan and Chyba (1997) [287] proposed that the early Earth had an organic haze layer in its atmosphere. Such a layer can be found in the atmosphere of Titan, the largest satellite of Saturn and is produced by methane photolysis in the presence of nitrogen. An organic haze layer would preferentially absorb ultraviolet light, thereby allowing ammonia and methane to persist in the atmosphere. 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

With the addition of CO caused by photochemical oxidation of methane, a significant flux enters the atmosphere annually, but the principal global contributions are terrestrial, anthropogenic and from atmospheric photolysis of methane. 

The photolysis of benzobarrelene. A, has been studied in considerable detail. Direct photolysis gives C, but when acetone is used as a photosensitizer, the di-rc-methane rearrangement product B is formed. 

The proton NMR spectrum shows chem shifts of 6.93 5.957- (Ref 1). Photolysis with a Hg arc lamp gives N, nitrous oxide, methane, and ethane (Ref 2). It was found to produce colon and rectal carcinomas in rats after oral administration at 12mg/kg weekly, induction period 235 days (Ref 3)... 

At levels of nonmethane hydrocarbons where their reaction rates with HO are a significant fraction of the reaction rate of HO with CO and methane, it may happen that the clean-air HO concentration remains unchanged. This would result if the increase in HO removal by NMHC s is compensated by increasing HO sources such as aldehyde or ketone photolysis and reactions such as R21. These considerations are examined below. 

Investigation of direct conversion of methane to transportation fiiels has been an ongoing effort at PETC for over 10 years. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using li t, water, and a semiconductor photocatalyst. Research in our laboratory is directed toward ad ting the chemistry developed for photolysis of water to that of methane conversion. The reaction sequence of interest uses visible light, a doped tungsten oxide photocatalyst and an electron transfer molecule to produce a hydroxyl i cal. Hydroxyl t cal can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional wata- molecule to produce methanol and hydrogen. 

The catalysts were tested for their ability to c ytically photolyze water prior to their use in the methane conversion experiments. We were able to reproduce photolysis results reported in the literature [4] using these catalysts under similar conditions. 

Hixson<27) prepared the deuterio compound (31) and found that photolysis produced only compound (32) resulting from a di-n--methane rearrangement and not from a hydrogen migration ... 

S,y-Unsaturated ketones undergo a rearrangement that is formally like the di-77-methane photorearrangement. An example of this rearrangement is provided by the photolysis of l,2,4,4-tetraphenyl-3-butenone ... 

Schaifner and co-workers found that steroid (49) upon photolysis gave products (50) in which the —CD3 and —CH3 groups were scrambled. This would be consistent with a stepwise oxa-di-w-methane type mechanism. 

Early examples of the class of reactions now known as di-w-methane photo-rearrangements were reported by Griffin et a/.,<1,2) Zimmerman and co-workers,<3,4) Meinwald and Smith,(5) and Srinivasan and Carlough.(6) This rearrangement occurs upon photolysis of molecules having two unsaturated moieties bonded to a single saturated carbon atom. A typical example is as follows<6) ... 

Upon low conversion direct photolysis the cis isomer (10) gave only the cis isomer (12) and the trans isomer (11) gave only the trans isomer (13). The triplet sensitized reaction of (10) and (11) gave rise only to cis-trans isomerization. Thus the di-ir-methane photorearrangement from the triplet state cannot compete with triplet state deactivation via cis-trans isomerization (Zimmerman has termed this the free rotor effect). Several other examples of regio-specilicity and stereospecificity in di-w-methane photoreactions are as followsa8 a3) ... 

However, Zimmerman has shown that (15) is not formed via a di-7r-methane rearrangement by the photolysis of the dideuterio compound (17) ... 

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