Radicals ethylperoxy

Ethane. Ethane VPO occurs at lower temperatures than methane oxidation but requires higher temperatures than the higher hydrocarbons (121). This is a transition case with mixed characteristics. Low temperature VPO, cool flames, oscillations, and a NTC region do occur. At low temperatures and pressures, the main products are formaldehyde, acetaldehyde (HCHOiCH CHO ca 5) (121—123), and carbon monoxide. These products arise mainly through ethylperoxy and ethoxy radicals (see eqs. 2 and 12—16 and Fig. 1). 

Atkinson, D. B and J. W. Hudgens, Chemical Kinetic Studies Using Ultraviolet Cavity Ring-Down Spectroscopic Detection Self-Reaction of Ethyl and Ethylperoxy Radicals and the Reaction 02 + C2H5 - C2H502, J. Phys. Chem. A, 101, 3901-3909 (1997). 

Fenter, F. F., V. Catoire, R. Lesclaux, and P. D. Lightfoot, The Ethylperoxy Radical Its Ultraviolet Spectrum, Self-Reaction, and Reaction with HO, Each Studied as a Function of Temperature, . /. Phys. Chem., 97,"3530-3538 (1993). 

Maricq, M. M., and J. J. Szente, Kinetics of the Reaction between Ethylperoxy Radicals and Nitric Oxide, J. Phys. Chem., 100, 12374-12379 (1996). 

With smaller alkylperoxy radicals, however, fewer / -, y-, and 8-carbon atoms are available. Thus, for example, the 2-methylprop-l-ylperoxy radical, OOCH2CH(CH8)o, has no y- or 8-C atoms, and the / -C atoms carry primary hydrogen only. Isomerization of this alkylperoxy radical by 1,5 transfer of primary H competes only moderately successfully with isomerization by 1,4 transfer of tertiary H (Table III). In the ethylperoxy radical, only 1,4 H-transfer is possible. For these cases, then, hydrogen abstraction will be a more frequent mode of oxidation of the alkyl radical than for larger radicals, but the calculation suggests that it will account... 

Small radicals such as tert-butylperoxy and ethylperoxy can, however, react via 1,4 H-transfer only the strain energy involved in O-heterocycle formation is 28 kcal. per mole. In this case, k.4(x — 106 sec."1 whereas krta = 10r> 4 sec. 1 and when [02] = 200 mm. of Hg, ko[02] = 105,3 sec. 1, so that k.4ct < < (tkr,a + k [02]). The result is that in the oxidation of small alkyl radicals, the route via alkylperoxy radicals will be blocked because reverse Reaction —4 competes successfully with Reaction 5. Reaction 2 will thus be a more effective mode of reaction of alkyl radicals with oxygen and the conjugate alkene will be a major product. 

The ease of formation of /3-hydroperoxyalkyl radicals from the alkane increases with molecular weight as shown in Table 16. Thus, for example, isomerization involving 1 5 H-transfer is impossible for ethylperoxy and prop-2-ylperoxy radicals, while isomerization of the pent-2-ylperoxy radicals leads to the lowest molecular weight hydroperoxyalkyl radical which can be formed by initial attack at a secondsiry C—H bond followed by isomerization involving 1 5 H-transfer from another secondary C—H bond. 

Since the direct formation of the ethylhydroperoxy radical is improbable for the A" state, the question still remains as to how the ethylperoxy radical forms oxirane, which can be produced from C2H5 -I- 02( 2g) albeit in smaller yield than from C2H4 -I- HO2, as observed by Baldwin et al. [114]. Reaction (49b) must involve internal conversion from the A" to the A state. Such a process will occur with low probability because the density of states in the latter is smaller than that in the former, because of the difference in zero point energies. Nevertheless, internal conversion allows access from ground state reactants to the excited electronic state... 

The main products of this reaction are two radicals. Examination of the orbital symmetry of the excited state by which this reaction proceeds shows that the electron density on the O-atom is similar to that of the A state mentioned above. Furthermore, the ground state reactants are shown to correlate with ionic products. This latter abstraction is not seen for the reactants in reaction (55) as the products are of higher energy, however the cyclic transition state of reaction of the ethylperoxy radical allows a concerted reaction which does not involve the explicit formation of charged intermediates. 

In oxidative processing of higher alkanes, reactions under discussion also to a considerable degree determine the product distribution. Let us consider reactions of ethyl species as a representative example. First of all, as all reactions of C-centered radicals with oxygen, reaction between ethyl and 02 can proceed as a reversible formation of ethylperoxy radical... 

Other ROj Reactions. There is a limited number of rate constant measurements for the reactions of HCFC-based peroxy radicals with HO2 and O3. Whereas the removal of peroxy radicals is dominated by reaction with NO in NO,-rich environments, such as the urban atmosphere, the reaction with HO2 can become important in areas with low NO, levels. Preliminary rate constants exist for the reaction of HO2 with two halogenated ethylperoxy radicals. For CF3CCI2O2, Hayman et al. [90] report a rate constant of (1.9 0.3) x 10 cm s at 298 K. The measurements of Maricq et al. [118] provide a rate constant of (1.8 S) x cm s for the reaction between CFjCFHOj and HO2. The room temperature rate constant of 4.3 x 10 cm s is in good agreement with the value of 4 X 10 cm s reported by Hayman [119] for this reaction. 

Percent product distribution acetone 27.6 1.9, acetaldehyde 27.9 1.9, ethanol 3.3 0.3, 2-methyl-2-hydroperoxybutane 14.6 1.1, 2-methyl-2-butanol 14.1 1.7, 3-methyl-2-butanone 9.1 0.8, 3-methyl-2-butanol 3.3 0.3. Another product expected, 2-propanol, could not be quantified because its signal was overlapped by that of the parent hydro-carbon. Analysis of the product distribution suggests that the ratio of hydrogen abstraction probabilities at the primary, secondary and tertiary sites is 13 17 70. The production of ethanol indicates that ethylperoxy radicals are produced in addition to the initial primary 2-methyl-1-butylperoxy and... 

Determination of the rate constant ratio for the reactions of the ethylperoxy radical with NO and NO2,... 

Reactions of ethylperoxy and acetylperoxy radicals under NO rich conditions, in P.M. Borrell, P. Borrell, T. Cvitas, W. Seiler (eds), Proc. EUROTRAC Symp. 90, SPB Academic Publ., The Hague 1991, pp. 403-405. 

The UV absorption spectrum of the ethylperoxy radical and its self-reaction. Kinetics between 218 and 333 K,... 

The ethylperoxy radical Its ultraviolet spectrum, self-reaction and reaction with HO2, each studied as a function of temperature,... 

Electron transfer is considered to take place to the oxygen molecule to give the Oa radical with subsequent hydrogen-atom abstraction from the hydroxylamine yielding HOa and HNO. The mechanism of auto-oxid-ation of triethylborane in the presence of iodine has been described. Induction periods observed are dependent on the iodine oxygen concentration ratios, and a chain-reaction mechanism is proposed involving both ethyl and ethylperoxy-radicals. 

The suitability of Gaussian distribution functions to describe the shape and temperature dependence of the UV absorption continua of peroxy radicals has been investigated. The ethylperoxy radical was used as a test case. Its 298 K absorption continuum was found to be best described by a semilogarithmic Gaussian distribution function. A linear Gaussian distribution function performed less well but still... 

Under polluted conditions, peroxypropanoyl reacts with NO2 to form peroxypropanoyl nitrate (CH3CH2C(0)02N02, PPN), which, like PAN, acts as a reservoir for NO , in its long range transport. The peroxy radical reacts with NO to form the ethyl radical, which in turn reacts with O2 to form the ethylperoxy radical (Le CrSne et al., 2005) ... 

The CH3CH2C(0)0 radical will decompose, leading to the formation of ethylperoxy... 

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