Halogen-Oxygen Species

Dibeler, Reese, and Franklin47 obtained D FO—F = 64.6 kcal/mole from electron attachment measurements on F20. With this value, Atf2°98 FO becomes either 41.3 or 51.6 kcal/mole, respectively, depending on whether AFf298 F20 is —4.4 or +5.86 kcal/mole. 

Malone and McGee114 performed electron impact studies on F202 and found D FO—OF = 103.5 4.6 kcal/mole. The enthalpy of formation of F202 has been measured calorimetrically to be 4.73 + 0.30 kcal/mole A/f298 FO can be computed to be 54.1 kcal/mole. This value agrees with that obtained from A/f298 F20 = + 5.86 kcal/mole. 

On the other hand, Price, Passmore, and Roessler139 estimated D 0—F sj 52 kcal/mole from theoretical considerations based on comparison with related molecules A/f298 FO becomes 26.4 kcal/mole. On the basis of the infrared spectrum of FO at 4°K, Arkell, Reinhard, and Larson8 believed that it is not unlikely that the correct value for D 0—F  

Finally it should be realized that if the oxidation of CF3 radicals produces FO directly at 25°C, then the low value for A//298 FO must be correct for the reaction to be exothermic (see Sect. III-A). The various results are listed in Table XI. 

In conclusion, the direct evidence favors A/f298 FO 53 kcal/mole but a lower value cannot be ruled out, especially since appearance potential measurements may contain large errors. 

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ROS reactive oxygen species, VHOCs volatile halogenated organic compounds... 

Table X summarizes the enthalpies of formation for halogen-oxygen-carbon species.

Enthalpies of Formation of Halogen-Oxygen-Carbon Species... 

Table 5 lists parameters for a selection of halogen-bridged species with this type of asymmetry. The effect of multiply bonded oxygen is larger than the other ligands listed, and the comparison of oxide as part of the ligand, in the pentane-2,4-dionate complex,27 where the asymmetric Mo—Cl distances only differ by 0.091 A, with the oxide trichloride, where the difference is 0.44 A, is particularly striking. 

The synthesis, structure, and superoxide dismutase mimetic activity in vitro and the protection against reactive oxygen species in vivo of mononuclear copper complexes with 2-(4-methylphenylsulfamoyl)-6-nitrobenzothiazole have been reported [602], Like 1,2,3-benzoxadiazoles, nitroderivatives of 1,2,3-benzothiadiazoles were obtained on diazotization of the corresponding or/Zzo-aminothiophcnolcs [213, 218, 583], The initial or/Zzo-thiophcnols for this reaction were synthesized by nucleophilic substitution of halogen in ort/zo-halogenoanilines. It turned out that 4-nitro- and... 

Peracid epoxidation and indirect epoxidation via the halohydrin route normally display opposite diastereoselectivity. In the indirect epoxidation route, the steric course is normally controlled by the first step, the formation of the most stable halonium ion, and not by the second step, the (tranx-diaxial) attack by the (nucleophilic) oxygen species. However, the relative rates and equilibria of both steps depend on the source of positive halogen and the reaction conditions which strongly influence the obtained stereoselectivity (Tables 3 and 4, and Section 4.5.1.1.3,). 

Use of Halide Ions to Improve Selectivity. Earlier work has claimed that enhanced selectivities for alkene oxidation can be achieved by the inclusion of electronegative elements such as S, Se, or halogens. This has been reviewed elsewhere. " More recent work has demonstrated substantial improvements in selectivity for propene (25—70%) and isobutene (35—80%) oxidation when either chloride or bromide is present. Both elements are added to the catalyst in the form of trace levels of organo-halide in the process gas stream. The selectivity increase is the result of a decrease in the rate of complete oxidation rather than an increase in the partial oxidation rate. Since the reaction is first order in oxygen pressure and zero order with respect to alkene in the presence and absence of halide, the reaction mechanism is probably similar in both cases. In the light of Anshits recent work, the effect of the halide is presumably to reduce the relative number and/or reactivity of surface lattice oxygen species and thus reduce the amount of irreversibly adsorbed alkene. 

Since many cytochromes P450 are inducible, the amount of reactive oxygen species can increase by the effect of an inducer e.g. halogenated aromatic compounds, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (Al-Bayati and Stohs 1987), lindane (JUNQUEiRA et al. 1986, Videla et al. 1990), or phenobarbital (ScHOLZ et al. 1990). Lindane elicited a dose-dependent enhancement of total oxygen uptake by the isolated perfused rat liver, which was largely inhibited by 0.55 mM desferrioxamine (Videla et al. 1989). 

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