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). 

Enders and coworkers <96AG(E)1725> have developed an interesting general one-pot method for the asymmetric epoxidation of enones with oxygen in the presence of diethylzinc and (l ,/ )-N-methylpseudoephedrine (30), which provides a, P - epoxyketones in very high yield and high enantiomeric excess (e.g., 33 —> 34). The actual reactive species is believed to be the chirally modified alkoxy(ethylperoxy)zinc 31, which attacks the si face of the s-cis conformation of the (E) enones (cf. 32). 

Bayer and Schretzmann 25) came to the conclusion that reversible oxygenation is a characteristic property of group VIII metals. However, work has shown that the cadmium complex CdEt2 can take up dioxygen reversibly in the ratio 1 2 (Cd O2). But it was found that the oxygenated complex (II(P) or 11(G) orientation) can undergo spontaneous catalytic oxidation to form bis(ethylperoxy) cadmium ... 

In the epoxidation process (Figure 4.4), the oxygen of the enone s carbonyl function first coordinates with the zinc atom. The ethylperoxy anion then attacks the (3-position, which constitutes a Michael-type addition. The subsequent cyclization gives the epoxy ketone and the zinc alkoxide. 

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. 

Quecksilber Ethyl-(l-methyl-l-phenyl-ethylperoxy)- E13/1, 196 (Salzbildung)... 

German (l-Phenyl-ethylperoxy)-trimethyl- E13/1, 185 (Salzbil-dung)... 

Sulfonsaure 3-(l-Methyl-l-phenyl-ethylperoxy)-propan-Natrium-salz E13/1, 373 (Sulton -(- R —O —OH)... 

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. 

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