Ozonides special

See in this Vol under Ozonides. The following compds are of special interest ... 

Handhng ozonides even in small amounts demands special care. Thus, various ozonides can be innocuously synthesized, by passing ozone-enriched oxygen through dry solutions of the corresponding olefins at —78 °C, followed by low-pressure distillation below 60 to 70 For example, the FOZs of methylenecyclohexene and methylenecyclopentene... 

The ozonide ion O3 has been clearly characterized by EPR and reflectance spectroscopy. Labeling experiments with 170 indicate that the O3 species contains three inequivalent oxygens forming a bond angle of about 110° and that it decomposes slowly at room temperature to form O ". A second type of species has been reported as O3 but has very different characteristics, since it is stable only at low temperatures and labeling experiments with 170, which indicate two equivalent nuclei, are difficult to interpret the balance of the evidence points toward a more complex polyoxygen species (see Section V,A). The data for O4 indicates that it is likely to exist on the surface under special conditions and we expect to see this confirmed by further studies. 

The IR spectroscopy of the extremely unstable 1,2,3-trioxolanes (primary ozonides) has been possible only in the recent past when special low-temperature IR cells became available. These cells enabled the preparation of primary ozonides from alkenes and ozone in the spectrometer itself. As shown in Table 4, most of the primary ozonides studied by this... 

Ozonolysis produces peroxide intermediates that pose a potential explosion hazard. Formation of insoluble substances on the wall of the reaction vessel during ozonolysis points to solid peroxides and special care must be taken during workup. The solvent chosen should be able to dissolve not only the starting material, but also the ozonide and any peroxide substance formed. 

The first intermediate, which never has been isolated and therefore must be very unstable, is called the Primdrozonid or initial ozonide (1). Nothing can be said with certainty at this moment about its special structure. 

It can thus be seen that zwitterions IV and V would be stabilized by the interaction of the alcohol with them, and the ozonide would have no opportunity to form and decompose abnormally. Whether zwitterions IV and V are formed in equal amounts depends upon the groups which are attached to the double bond and the carbon atom to which the ozone molecule initially adds. The final products, VI and VII, may be considered as hemiperacetals or hemiperketals and could be isolated only under special conditions. However, they can be easily decomposed with either sulfurous acid or sodium bisulfite and the ketones or aldehydes formed determined quantitatively as their 2,4-dinitrophenylhydrazones. 

If the doubly bonded olefinic carbon atom carries no hydrogen, the product is always unambiguously a ketone but if the carbon atom carries one or more hydrogen atoms, the aldehyde first formed by the oxidation may react further to give an acid. Aldehydes can only be obtained with certainty by use of ozone and special techniques for cleavage of the ozonide when other oxidants are used, olefins actually give aldehydes only when specific constitutional requirements are fulfilled. 

A special use for organophosphites is the production of singlet oxygen 02( D) which has sufficient lifetime to participate in chemical reactions. It is obtained by decomposition of the ozonide R = Ph (12.304). 

A few other special procedures are quoted elsewhere in this book Methods for preparing ozonides (pp. 406—409) and for formation of mercury(II)-acetate adducts of unsaturated lipids (p. 402) procedures for esterifying fatty acids with diazomethane (p. 175) and for acetylation of alcohols with acetic anhydride (p. 175). The procedures described for preparing trifluoroacetates or trimethylsilyl ethers can be applied to aliphatic alcohols. 

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