Ozone protonated

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Protonated Ozone. Gaseous ozone can be protonated with strong Briimsted acids,, eg,, KrH , XeH , and CH, according to the reaction + O3 A + O3. Protonated ozone reacts exothermically with methane 03 + CH — CH3 + H2O + O2, followed by... 

Oxygen Compounds. Although hydrogen peroxide is unreactive toward ozone at room temperature, hydroperoxyl ion reacts rapidly (39). The ozonide ion, after protonation, decomposes to hydroxyl radicals and oxygen. Hydroxyl ions react at a moderate rate with ozone (k = 70). 

Protic acids, in cationic polymerization of cyclic siloxanes, 22 560 PROTO (-)-Protoemetine, 2 84, 85 Protonated ozone, 7 7 774-775 Protonated pyridines, 27 100-101 Protonation, 75 653-654... 

Protons attached to the C atoms of the 1,2,4-trioxolane moiety of FOZs have chemical shifts at distinctly lower field than alcohols, ethers or esters. For example, the chemical shifts of the ozonide product in equation 100 (Section Vin.C.b.a) are S (CDCI3) 5.7 ppm for the H atoms of the trioxolane partial structure, and 4.1 ppm for the protons at the heads of the other ether bridge . Measurement of the rate of disappearance of these signals can be applied in kinetic studies of modifications in the ozonide structure. The course of ozonization of the methyl esters of the fatty acids of sunflower oil can be followed by observing in H and C NMR spectra the gradual disappearance of the olefinic peaks and the appearance of the 3,5-dialkyl-1,2,4-trioxolane peaks. Formation of a small amount of aldehyde, which at the end of the process turns into carboxylic acid, is also observed . 

The product of the one-electron reduction of O2, the superoxide ion, Oi, is highly unstable in acidic-aqueous solutions where its protonated form, the peroxyl radical H02(pA = 4.8), decomposes to ozone, oxygen, and hydrogen peroxide experiments have shown that the two latter compounds are produced almost quantitatively, when only traces of ozone are found. In alkaline solutions, the superoxide ion is more stable even if it decomposes spontaneously to O2 and H02 (AG-6-=—51.13 kj mol ), it has been studied by polarography in NaOH solutions, in the presence of compounds that adsorb at the surface of the electrode and slow down the protonation of 02 . From these electrochemical experiments... 

Finally, the idea of the coupling between nucleophilic attack and proton transfer in the reaetions just discussed provides an interpretive framework for another important atmospheric reaction, namely the hydrolysis of dinitrogen pentoxide N2O5, thought to play an important role in mid-latitude global ozone depletion. 28,29 Indeed a related mechanism was suggested in ref 5 for the low acidify condition hydrolysis. 

Increased production of oxides of nitrogen through solar proton events associated with the 11-year cycle in solar activity would be expected to be most important in the upper stratosphere, above the region where the majority of the ozone depletion was observed in addition, lower, rather than higher, concentrations of gas-phase oxides of nitrogen appear to be associated with the ozone depletion (e.g., see Noxon, 1978 McKenzie and Johnston, 1984 Thomas et al., 1988 Keys and Gardiner, 1991 and Solomon and Keys, 1992). Hence both of these explanations are not consistent with atmospheric observations. 

When methane is reacted with ozone in superacidic media,61,67 formaldehyde is directly formed through a pathway that is considered attack by +03H into a C—H bond, followed by cleavage of H2O2 to give very reactive methyloxenium ion (2), which instantly rearranges to protonated formaldehyde ... 

It should be mentioned that with superacidic electrophilic oxygenation of methane either to methanol (with protonated hydrogen peroxide) or to formaldehyde (with protonated ozone), the products formed are indeed the protonated products (CH3OH2 and CH2=OH+, respectively), which are protected from further electrophilic oxygenation, which happens only too readily in conventional oxidations. 

In electrophilic oxygenation with ozone in superacidic media or in dry ozonation over silica gel, protonated ozone, namely, +C>3H, was suggested to be the de facto electrophile. These reactions are fundamentally different from conventional ozonations with O3, which is a highly dipolar molecule. In 03H+ the dipole is removed by protonation. Cacace and Sporenza were able to directly identify +C>3H in the gas phase and also measure the proton affinity of ozone.107... 

Dimethylbutane and 2,3-dimethylbutane in Magic Acid—S02C1F solution at —78°C give the same distribution of products, a roughly 3 2 mixture of dimethyl-isopropylcarboxonium ion (19) and protonated acetone (20)67 (Scheme 9.5). This clearly demonstrates that, in contrast with the transformation of the abovementioned compounds, ozonation in this case proceeds via the intermediate carbocation 18. 

Dimethylpropane91 (neopentane) is transformed to a mixture of ethyldi-methylcarboxonium ion (21) and dimethylmethylcarboxonium ion (15). At —78°C 21 is formed exclusively. At temperatures higher than -20°C, 15 becomes the predominant product. Formation of 21 can be best explained by a reaction path that involves insertion of protonated ozone into the C—H a bond, formation of the tert-amyl cation through rearrangement, and its quenching by ozone ... 

Similar mechanisms account for the formation of the same products from 2,2,3,3-tetramethylbutane. Besides these predominant pathways, other reactions such as insertion of protonated ozone into the C—C bond and protolysis of the C—H bond may also take place. 

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