Methyl radical reaction with hydroxyl

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. 

Good, D.A., Hanson,]., Francisco, ].S., Li, Z., andjeong, G.-R. Kinetics and reaction mechanism of hydroxyl radical reaction with methyl formate, J. Phys. Chem. A, 103(50) 10893-10898, 1999. 

Arif, M., Dellinger, B., Taylor P.H. (1997) Rate coefficients of hydroxyl radical reaction with dimethyl ether and methyl fert-butyl ether over an extended temperature range. J. Phys. Chem. A 101, 2436-2441. 

In bleomycin-mediated degradation of DNA, the predominant pathway for base release has been shown to involve formation of radicals at C-4 of the nucleotides, the sugar produced being 2-deoxypentos-4-ulose.253 By examination of three adducts formed with the trapping agent 2-methyl-2-nitrosopropane, abstraction of hydrogen atoms from C-1 , C-4 and C-5 in thymidine 5 -monophosphate was detected in its reaction with hydroxyl... 

Carrasco, N., J.E. Doussin, M. O Connor, J.C. Wenger, B. Picquet-Varrault, R. Durand-Jolibois, and P. Carlier (2007a), Simulation chamber studies of the atmospheric oxidation of 2-methyl-3-buten-2-ol reaction with hydroxyl radicals and ozone under a variety of conditions J. Atmos. Chem., 56, 33-55. 

A similar intramolecular oxidation, but for the methyl groups C-18 and C-19 was introduced by D.H.R. Barton (1979). Axial hydroxyl groups are converted to esters of nitrous or hypochlorous acid and irradiated. Oxyl radicals are liberated and selectively attack the neighboring axial methyl groups. Reactions of the methylene radicals formed with nitrosyl or chlorine radicals yield oximes or chlorides. 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

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. 

Reaction of hydroxyl radicals with methyl methanethiolsulfinate has also been studied (Gilbert et al., 1976). Evidence for the occurrence of both reactions (83a) and (83b) was obtained. 

Of course, all the appropriate higher-temperature reaction paths for H2 and CO discussed in the previous sections must be included. Again, note that when X is an H atom or OH radical, molecular hydrogen (H2) or water forms from reaction (3.84). As previously stated, the system is not complete because sufficient ethane forms so that its oxidation path must be a consideration. For example, in atmospheric-pressure methane-air flames, Wamatz [24, 25] has estimated that for lean stoichiometric systems about 30% of methyl radicals recombine to form ethane, and for fuel-rich systems the percentage can rise as high as 80%. Essentially, then, there are two parallel oxidation paths in the methane system one via the oxidation of methyl radicals and the other via the oxidation of ethane. Again, it is worthy of note that reaction (3.84) with hydroxyl is faster than reaction (3.44), so that early in the methane system CO accumulates later, when the CO concentration rises, it effectively competes with methane for hydroxyl radicals and the fuel consumption rate is slowed. 

Absolute rate constants have been measured for the gas-phase reactions of hydroxyl radical with five methyl ketones, MeCOR R=Me, Et, and (CH2) CHMe2(K = 0, 1,2).i55... 

Table HI illustrates that cobalt behaves as an extraordinary catalyst in its reaction with MCPBA increasing the rate by a factor of 400,000 and reducing the activation from 27 to 9.5 kcal/mol. However, cobalt also greatly enhances the selectivity in the system (Table HI). The yield to the desired acid increases from 89% to 100% with the expected decrease in the by-products. The thermal decomposition of MCPBA, equation 2, releases the hydroxyl radical which can easily attack the acetic acid forming carbon dioxide and methyl acetate.

Bierbach, A., I. Barnes, and K. H. Becker, Rate Coefficients for the Gas-Phase Reactions of Hydroxyl Radicals with Furan, 2-Methyl-furan, 2-Ethylfuran, and 2,5-Dimethylfuran at 300 + 2 K, Atmos. Environ., 26A, 813-817 (1992). 

I have spent some time trying to explore the experimental basis for such a reaction, and at the moment I feel that there is no good experimental foundation for writing it. From a structural point of view, it appears to be a highly unlikely reaction. The simplest example of such a reaction would be the reaction of methyl radicals with oxygen to produce formaldehyde, plus hydroxyl radical (Reaction 8)... 

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