Anions ozonide

The preparation, properties and uses of ozonides have been reviewed comprehensively [1]. Many pure ozonides (trioxolanes) are generally stable to storage some may be distilled under reduced pressure. The presence of other peroxidic impurities is thought to cause the violently explosive decomposition often observed in this group [2], Use of ozone is not essential for their formation, as they are also produced by dehydration of c cF-dihydroxy peroxides [3], A very few isomeric linear trioxides (ROOOR) are known, they are also explosively unstable. Inorganic ozonides, salts of the radical C>3 anion, are also hazardous. 

Cyclic enones can be oxidatively cleaved by a range of reagents to yield keto acids. As ozonolysis can be quite hazardous for large-scale preparations with the build up of ozonides, the procedure has been modified using quaternary ammonium salts to catalyse the transfer of peroxide anion for a rapid oxidative work-up [32]. Two methods are available but, in the safer procedure (10.7.15.A), there is no effective build-up of the ozonide. 

Ozone, 17 63 depletion, 46 109-110 fluoride, see Trioxygen difluoride Ozonide radical anion, chemistry, 33 76... 

Tetracyanoethylene complexes, disilanes, 816 Tetracyclone, bleaching, 734-5 Tetraethylammonium ozonide, 736 Tetragermabuta-1,3-diene, 825, 826 Tetrahedral distortion acychc organic peroxides, 103 alkyl hydroperoxides, 110 anion ligands, 119... 

The ozonide anion radical (030-) formed by the reaction between ozone and the superoxide... 

The decomposition of ozone is catalyzed by the hydroxide ion. Ozone dissociates in the presence of OH to H02°/02°. Further decomposition via the ozonide anion radical 03°7 HO,° results in the formation of OH° (see Figure 2-1, Part A, p. 11). They may react with organic compounds, radical scavengers (HC03, C032-) or ozone itself. 

The reaction shown in Eq. (99) is fast, with a bimolecular rate constant of 3.6xl010 L mol 1 s, and the product is the ozonide anion. Ozonation has an additional benefit. Ozonide decomposes [shown in Eqs. (100) and (101)] to hydroxyl radical and oxygen [56], increasing the oxidative power of the solution by a second mechanism ... 

The presence of two O—O bonds renders primary ozonides so unstable that they decompose immediately (Figures 15.47 and 15.48). The decomposition of the permethylated symmetric primary ozonide shown in Figure 15.47 yields acetone and a carbonyl oxide in a one-step reaction. The carbonyl oxide represents a 1,3-dipole of the allyl anion type (Table 15.2). When acetone is viewed as a dipolarophile, then the decomposition of the primary ozonide into acetone and a carbonyl oxide is recognized as the reversion of a 1,3-cycloaddition. Such a reaction is referred to as a 1,3-dipolar cycloreversion. 

The chemistry of the ozonide radical anion has been discussed in Czapski s review (88), but the chemistry is complex, and the interested reader should consult more recent sources (282). The potential of the 03/03 couple has not been the subject of repeated scrutiny. Klaning et al. recently measured it by investigating reaction 10 (182). Their value of 1.01 V leads to AfG° = 77 kJ/mol for 03 these results are probably fairly accurate because they confirm the potential of the OH/OH" couple. There is considerable uncertainty expressed in Czapski s review concerning the pKa of H03 (88) on the basis of chemical analogy he estimated a pKa of — 2. In a recent investigation it was asserted that H03 has a pK of 6.15, although it splits into OH and oxygen before it has time to dissociate into 03 (60). Subsequently the pKa was corrected to 8.2 + 0.1 (61). It is prudent to await confirmation of these results. 

A varying and much more complex mechanistic situation exists in heterogeneous photocatalysis (Fig. 5-13). With respect to the transient oxygen species, comparable overall oxidation reactions are usually observed, but the set of primary reactive oxygen species is slightly different. It is commonly assumed, that superoxide radical anions and hydroxyl radicals are the primary species formed after photogeneration of the electron-hole pair of a semiconductor catalyst in the presence of water and air (Serpone, 1996). In the presence of ozone, ozonide radical anions or are formed by fast electron transfer reaction of superoxide radical anions with O3 molecules. The combination Ti02-03-UV/VIS is called photocatalytic ozonation (Kopf et al., 2000). For example, it was applied for the decomposition of tri-chloroethene in the gas phase (Shen and Kub, 2002). 

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