Benzene reaction with oxygen atoms

FIGURE 18.9 An Arrhenius plot of In k against 1/Tfor the reaction of benzene vapor with oxygen atoms. An extrapolation to 1/T = 0 gives the constant In A from the intercept of this line. 

Boocock, G., and R. J. Cvetanovic. Reaction of oxygen atoms with benzene. Can. 

Also to be mentioned are the reactions of oxygen atom radical anions with organic substrates. These reactions were reviewed by Gronert (2001). For the reactivity of the atomic oxygen anion-radical, see Section 1.7.2. The atomic oxygen anion-radical reacts with benzene, tetramethylene ethane, or cyclopentadienylidene trimethylenemethane. The reactions consist in abstraction of H2 with the formation of H2O and the corresponding distonic anion-radicals as products. 

A Pulsed-Radiolysis Study of the Gas-Phase Reaction of Oxygen Atoms with Benzene and Related Compounds Rate Constants and Transient Spectra... 

Figure 1. Transient absorption spectra resulting from reaction of oxygen atoms with benzene, toluene, and ethylbenzene...

The equilibrium is about 2 1 in favor of B at room temp, in isooctane solution. As will be discussed in the section on transient decay, these species are possible products of the reaction of oxygen atoms with benzene. In addition, the biradical (C) produced... 

Relatively few reports appeared on oxepine systems in 2004. The preparation of benzene oxide/oxepine has been observed in the gas phase reaction of benzene with oxygen atoms. Further reaction of this product with these atoms then gave a mixture of products including a compound thought to be oxepin-4,5-epoxide or oxepin-2,3-epoxide <04MI391>. Of relevance to this work is the report of the first observation of a 4,5-benzoxepin-2,3-oxide by H NMR <04TL4789>. Other fused systems have been of interest. The synthesis of a novel bicyclic oxepinopyrimidine 62 has been described. Acetylation of the alcohol 60 afforded the acetate derivative 61 which was then cyclised to the oxepine derivative 62 plus 63 on treatment with concentrated HCl <04H(63)2523>. 

Upon careful analysis, the product was found to be a macrocycle containing two benzene rings, six oxygen atoms, and ethylene spacers between the oxygens. It had formed through the reaction of diethylene glycol dichloride and catechol. Pedersen had known that the 2-(hydroxyphenoxy)tetrahydropyran was contaminated with about 10% of the unprotected catechol but had decided to proceed with the reaction in any case. Following his chance result Pedersen carefully repeated the experiments... 

Tris(2,4-pentanedionato)iron(III) [14024-18-1], Fe(C H202)3 or Fe(acac)3, forms mby red rhombic crystals that melt at 184°C. This high spin complex is obtained by reaction of iron(III) hydroxide and excess ligand. It is only slightly soluble in water, but is soluble in alcohol, acetone, chloroform, or benzene. The stmcture has a near-octahedral arrangement of the six oxygen atoms. Related complexes can be formed with other P-diketones by either direct synthesis or exchange of the diketone into Fe(acac)3. The complex is used as a catalyst in oxidation and polymerization reactions. 

It should be expected that the orientation and rate of electrophilic substitution in the isoxazole nucleus would be affected by both hetero atoms. Because of the electron-accepting effect of the nitrogen atom, electrophilic substitution of the isoxazole nucleus should proceed less readily than in the case of benzene and should occur essentially at the position jS to the nitrogen atom, just as in pyridine and other azoles. Simultaneously the electron-donating oxygen atom should facilitate such reactions in isoxazole as compared with the substitution in pyridine. These predictions are confirmed by the available experimental evidence. 

A The Mannich reaction proceeds through the intervention of the N,A dimethylmethyleniininium cation [Me N =CHJ, This is insufficiently electrophilic to react with the benzene ring under the mild reaction conditions. Similarly, were the electrophile to react with the carbonyl oxygen atom of the heterocycle, this reaction would be reversible, as an aminomethyl ether is relatively unstable in acidic media. Thus, it seems plausible that the chromone utilizes enol or enolate character to trap the electrophile at C-3, followed by deprotonation of the adduct to reform the chromone ring system ( heme 5.9). 

More recently, photochemical reactions of 138 with cyclic and acyclic olefins have been described. When 138 is irradiated (Pyrex) with cyclo-heptatriene, [4 + 4]- and [4 + 6]-adducts (247-250, Scheme 16) are obtained in addition, photodimer 242 and o-dibenzoylbenzene (140) were isolated. The ratio of the [4 + 6]-adducts to the [4 + 4]-adducts [(249 + 250)/(247 + 248)] is increased in air-saturated benzene solutions compared with oxygen-free benzene solutions, and enhanced in heavy atom solvents (e.g., chloroform compared with cyclohexane) furthermore, this ratio is decreased in the presence of the triplet quencher azulene. These observations suggest that [4 + 6]- and [4 + 4]-adducts are formed by different mechanisms. 

Besides the oxygen atom reactions discussed earlier, we studied those involving I.2-C2H4CI2,66 NH3,66 and acetylene, cyclohexane, and benzene. At first attempts were made to find an O atom reaction that would be similar and at the same time essential for all substances. This is the ease, for example, for hydrogen atoms and hydroxyl. Hydrogen reacts with saturated hydrocarbons by abstraction of the H atom, and with unsaturated hydrocarbons by addition as well. Hydroxyl is believed to react with hydrocarbons by abstraction of the H atom and formation of water. 

---