Group ozonides

Ozone cracking is a physicochemical phenomenon. Ozone attack on olefinic double bonds causes chain scission and the formation of decomposition products. The first step in the reaction is the formation of a relatively unstable primary ozonide, which cleaves to an aldehyde or ketone and a carbonyl. Subsequent recombination of the aldehyde and the carbonyl groups produces a second ozonide [58]. Cross-linking products may also be formed, especially with rubbers containing disubstituted carbon-carbon double bonds (e.g. butyl rubber, styrene-butadiene rubber), due to the attack of the carbonyl groups (produced by cleavage of primary ozonides) on the rubber carbon-carbon double bonds. 

The low value of the expl power of oxygen atoms bonded with carbon and hydrogen atoms in such a group as COOH had already been stressed by Stettbacher (Ref 2), who also pointed out that an exception is provided by peroxides and ozonides which form exothermic bonds that considerably enhance expl performance... 

Hydrolysis, or better, hydrogenolysis of the normal ozonide leads to the cleavage of the original carbon-carbon double bond with formation of carbonyl groups. The abnormal ozonide usually decomposes before it reaches room temperature and both the double bond and the adjacent carbon-carbon single bond are found to have cleaved. 

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. 

Fajgar, R. Roithova, J. Pola, J. Trimethylsilyl Group Migrations in Cryogenic Ozonolysis of Trimethylsilylethene Evidence for Nonconcerted Primary Ozonide Decomposition Pathway. . Org. Chem. 2001, 66, 6977-6981. 

Most of the examples given here involve fairly strong acid catalysts to effect fragmentations. Many ozonides are stable to mild acids, so that if a molecule contains other functionality, chemoselective reactions are possible. Reactions of compounds containing both an aldehyde and ozonide group (88) have been studied. The aldehyde could be protected as an acetal using ethylene glycol with... 

Following this work on NMR spectra of ozonides, there is an extensive paper by the Griesbaum group" where 35 ozonides (6-14 with different stereochemistries) have been studied. The widely different structures examined allowed the influences of structural features on "O NMR spectra of ozonides to be shown. Five structurally different types of ozonides can be recognized symmetrically tetrasubstituted (type 6), unsymmetrically tetrasubstituted (type 7), unsymmetrically tri- and tetrasubstituted (type 8), unsymmetrically disubstituted (type 9-13) and bicyclic ozonides (type 14). "O NMR chemical shifts of peroxidic and ethereal oxygens are collected in Table 3. All spectra were obtained at natural isotopic abundance, in benzene-dg solution mainly at 25 °C, although in some cases higher temperatures had to be used. These experimental conditions make for an easy comparison with the previously discussed data. 

O NMR spectroscopy of organic compounds containing the —0—0—group 175 TABLE 3. NMR data of ozonides 6-14"... 

The ozonides of indenes substituted with bulky alkyl groups in the aUylic position (e.g. 261) nndergo acid-catalyzed dimerization to a 10-membered endoperoxide (262), as shown in eqnation 90. Similarly to equation 89, the process involves hydroperoxide... 

The ozonides of choline and ethanolamine phosphatides subjected to reduction with PhsP yield the corresponding core aldehydes. After hydrolysis with phospholipase C to eliminate the polar group and silylation with trimethylsilyl chloride, the core aldehydes can be determined by GLC-FID using temperature programming to high temperatures . ... 

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