CH3O with radicals, reactions

The analysis of this model revealed some interesting qualitative effects, which were experimentally verified later. The competition of reactions (2) and (3) of active methoxy radicals CH3O with methane and oxygen... 

The near-u.v. photolysis of methyl nitrite yields methoxy radicals [equation (10)] with a quantum yield of unity. Reaction rate constants of CH3O with Oj... 

For example, with the simplest alkoxy radical, methoxy (CH3O), the following reaction occurs,... 

Direct measurements were made for the reactions of CH3O with O2 by monitoring the radical concentrations (Gutman et al., 1982). The CH3O radicals were produced by the 266-nm photolysis of CH3ONO. The rate coefficient for the CH3O + O2 reaction from feeir study along with the results of several other... 

Lorenz et al. (1985) measured the rate coefficients for the reaction of CH3O with O2 at 300-5(X) K using laser flash photolysis of CH3ONO at 248 nm. The CH3O radicals were monitored by laser-induced fluorescence. The rate coefficient... 

Attempts to measure the rate coefficient for the reaction of CH3O with O3 have shown that the reaction is immeasureably slow at room temperature. Simonaitis and Heicklen (1975) i epated CTI3O from the reactions of 0( D) with CH4 and the subsequent oxidation of the CH3 radical produced in the reaction. They found no reaction at 25°C and estimated the upper limit to be 1.2 X l0 Af -sec . ... 

Fortuno (1982) produced CH3O radicals in a flow tube from the reaction of F atoms with CH3OH. He monitored the CTI3O directly by laser magnetic resonance and could see no reaction of CH3O with O3. His upper limit for the reaction was 3.0 x lO 3/ -sec. ... 

There are some competing reactions with (5.43), which we will discuss in Chapter 5.3.3. But when the methoxy radical CH3O is produced, reaction (5.45) rapidly proceeds and gives formaldehyde, HCHO and HO2, closing the HOj, cycle ks,4s = 1.9 10" cm molecule" s" at 298 K) ... 

The branching ratio P generally increases with the chain length of the aliphatic hydrocarbon. The rate constants for the reactions of the oxy radicals with O2 appear to be independent of the nature of the oxy radical (excl. CH3O) with (02) = (8 2) X cmVs, whereas the overall rates of decomposition and isomerisation depend both on the chain length and the structure of the radical. 

At low temperatures, typical of barrier-discharge conditions, reaction of methoxy radical CH3O with methane, the main channel for the formation of methanol at higher temperatures, has a very low rate constant. Therefore, the mechanism of methanol formation under these conditions is likely to differ from the mechanism of its formation in the thermal partial oxidation of methane. This is evidenced by a significantly higher ( 15%) oxygen concentration at which the maximum selectivity to methanol is achieved (Figs 9.14 and 9.15). Therefore,... 

The reactions of this radical may be important in ignition processes (Gardiner et al, 1981) since CH3O is formed in the reaction of CH3 with O2 (see above). The reaction with H atoms is known to be fast, whereas that with O atoms is relatively slow. No information is available for the corresponding OH reaction. These radical-radical reactions compete with the reaction with O2 (Fig. 49) and with the thermal decomposition (Fig. 50). In both cases, the high-temperature measurements show large discrepancies. 

Reactions with molecular species above the arrow e.g. RIO) involve subsequent reactions with these species to produce the indicated products. In most cases the reactants shown to the left of the arrow participate in the slowest or rate-determining step]. The CH3O radical formed in Rll then follows reaction R7. The H02 radical formed in RIO is the other member of the family and is linked with HO in a variety of chain reactions. These radicals are produced following HO attack on hydrocarbons or by photodissociation of oxygenated hydrocarbons such as formaldehyde (RIO) and acetaldehyde ... 

Br-atom initiated oxidation of dimethyl sulfide (DMS) in a large-volume reaction chamber gave SO2, CHsSBr, and DMSOJ A rapid addition of Br atoms to DMS takes place, forming an adduct that mainly reforms reactants but also decomposes unimolecularly to form CHsSBr and CH3 radicals. DMSO is formed from the reaction of BrO radicals with DMS. The reaction CH3O2 + Br CH3O + BrO is postulated as the source of BrO radicals. 

The two isomers CH3O and CH2OH have quite different reaction characteristics. The hydroxymethyl radical mainly reacts with oxygen to form the second desired end product, formaldehyde ... 

This reaction competes favorably with other CH3O2 reactions, such as (R16) and (R20), and offers a fast pathway to the methoxy radical (CH3O). In a similar reaction, nitric oxide converts the hydroperoxy radical (HO2) to the more reactive hydroxyl radical,... 

The alkoxy radicals formed in pathway Eq. 26a have very interesting atmospheric chemistry. The atmospheric fate of alkoxy radicals differs with the nature of the R group. Some alkoxy radicals (e.g., CH3O) are lost solely via reaction with 02, others undergo rapid decomposition via C-C bond scission. Long chain alkoxy radicals can undergo isomerization via intramolecular H-atom abstraction ... 

Two-laser two-photon results revealed photoisomerization of the cation E,E-11 to its stereoisomer Z,E-11, which undergoes thermal reversion with a lifetime of 3.5 ps at room temperature. Absolute rate constants for reaction of styrene, 4-methylstyrene, 4-methoxystyrene and /i-methyl-4-methoxystyrene radical cation with a series of alkanes, dienes and enol ethers are measured by Laser flash photolysis [208]. The addition reactions are sensitive to steric and electronic effects on both the radical cation and the alkene or diene. Reactivity of radical cations follows the general trend of 4-H > 4-CH3 > 4-CH3O > 4-CH30-jff-CH3, while the effect of alkyl substitution on the relative reactivity of alkenes toward styrene radical cations may be summarized as 1,2-dialkyl < 2-alkyl < trialkyl < 2,2-dialkyl < tetraalkyl. 

Both of these early studies established the importance of the reaction of alkoxyl radicals with O2. Ho ever, as we shall see, the estimates of the rate coefficients were much too low. A further study which indicated that 1-C3H7O reacted with O2 was done by Milne and Steel (1968), who photooxidized azoisopropane at 25 and —27°C. Recent work (Zellner, 1986) in which both CH3O and CH2O were measured by laser-induced fluorescence gave a yield of 0.85 0.15 for CH2O from the 62 + CH3O reaction. 

The rate constant of the self-reaction was obtained by the modulated photolysis technique combined with long path UV absorption spectroscopy. Absorption-time profiles, obtained at various wavelengths, were analysed with the help of computer simulation. The presence of HO2 radicals must be taken into account in the kinetics analysis, since they are generated by reaction (2) of CH3O radicals with O2, emphasising the importance of the knowledge about channel (la) ... 

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