Criegee mechanism of ozonolysis

The Criegee mechanism of ozonolysis characterizes the interaction of dipolar, electronically deficient ozone with the Jt-electron-rich C=C bond forming a cyclic intermediate [16, 17]. It rearranges with insertion of an O atom into the C-C bond and finally hydrolyzes in two moles of carbonyl compound with the formation of one mole of hydrogen peroxide. This mole of peroxide acts in situ as an oxidant of aldehyde to the carboxylic group. Oxidation of aldehydes can be completed with a number of reagents two are cited in Scheme 5.56. 

FIGURE 8-2 Mechanism of ozonolysis. A, Criegee zwitterion B, aldehyde C, ozonide. 

T he Criegee (1) mechanism of ozonolysis postulates that unsymmetrical olefins should give two zwitterions and two carbonyl compounds and hence postulates the possible formation of three different ozonides. This prediction has now been realized in a number of cases (2-9). It has also been shown that in many cases the ozonide stereoisomer ratio depends upon olefin stereochemistry in both normal (3, 6-12) and cross (6-9) ozonides. Since the original Criegee mechanism did not provide for these stereochemical results, a number of additional suggestions for the mechanism have been made (6,9,13, 14), all of which retain the fundamentals of the Criegee mechanism. 

During the past seven or eight years some excellent and novel studies have cast doubt upon the Criegee mechanism as the sole mechanism of ozonolysis. All of the newer mechanisms proposed, however, have ac-... 

The reactions of O3 with C3H6, 9 and 10, were based on a review of the mechanism of ozonolysis by Murray (15). The accepted mechanism in the gas phase is similar to that commonly referred to as the Criegee mechanism in the liquid phase. The attack of O3 on C3H6 is electrophilic, and Vrbaski and Cvetanovic (16) have correlated the electrophilic behavior with that of oxygen atom-olefin reactions. Both reaction rates correlate with the ionization potentials of a series of olefins. 

Chapman JR (1985) Practical organic mass spectrometry. John Wiley, Chichester, 197 pp Criegee R (1975) Mechanism of ozonolysis. Angew Chem Int Ed Engl 14 745-751 Deslongchamps P, Atlani P, Frehel D, Malaval A, Moreau C (1974) The oxidation of acetals by ozone. Can J Chem 52 3651-3664... 

Criegee, R. (1975). Mechanism of ozonolysis. Angew. Chem. Int. Ed. Engl. 14, 745-751. Cronn, D. R., R. J. Charlson, R. L. Knights, A. L. Crittenden, and B. R. Appel (1972). A Survey of the molecular nature of primary and secondary components of particles in urban air by high resolution mass spectroscopy. Atmos. Environ. 11, 929-937. 

Criegee (2) mechanism of ozonolysis allows for the possibility of two zwitterions and two carbonyl moieties upon ozonolysis of an unsymmetrical olefin. This possibility leads to the prediction that such ozonolyses could lead to the production of three ozonide cis-trans pairs. 

Targely based on our finding that the cis/trans ratios of cross ozonides 10) formed from unsymmetrical olefins depended on olefin geometry 11, 12), we have proposed a new mechanism of ozonolysis which takes account of this effect 14). The new mechanism, which considers only a limited type of olefin, namely trans-disubstituted and relatively unhindered cis olefins, differs significantly from the generally accepted Criegee mechanism 1,5). 

Using modern analytical methods, a number of transient intermediates and byproducts could be verified [19, 20]. The first step in the mechanism of ozonolysis is the 1,3-dipolar cycloaddition of the dipole ozone to the double bond of OA. A 1,2,3-trioxolane is formed, the unstable primary ozonide or molozonide. The primary ozonide collapses in a 1,3 dipolar cycloreversion to a carbonyl compound and a carbonyl oxide, the so-called Criegee zwitterion. Since OA is substituted with two diverse groups at the double bond, two different opportunities exist for the formation of carbonyl compound and carbonyl oxide. Again, a 1,3-dipolar cycloaddition of these intermediates leads to three different pairs of 1,2,4-trioxolane derivatives (cisltram), the secondary ozonides, which are more stable than the primary ones. Their oxidative cleavage results in AA and PA. 

The formation of metallocyclic complexes by addition of ketones to dioxygen complexes resembles a three-step Criegee mechanism for ozonolysis. " " In each case one envisages the formation of a dipolar 0-0 bond that leads to electrocyclic ring closure with the ketone. No proven oxidation of aldehydes or ketones has yet been achieved with these metal-locycles. Nevertheless, in the catalytic conversion of cyclic ketones to lactones using hydrogen peroxide and a molybdenum complex as catalyst, it is believed that such an intermediate metallocycle is first formed and that it subsequently converts to lactone and molybdenyl products (16). " ... 

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