Ozonolysis dioxirane

The ozonolysis of ethylene in the liquid phase (without a solvent) was shown to take place by the Criegee mechanism.This reaction has been used to study the structure of the intermediate 16 or 17. The compound dioxirane (21) was identified in the reaetion mixture at low temperatures and is probably in equilibrium with the biradical 17 (R = H). Dioxirane has been produced in solution but it oxidatively cleaves dialky] ethers (such as Et—O—Et) via a chain radical process, so the choice of solvent is important. 

The parent dioxirane (DO) was synthesized by gas-phase ozonolysis and characterized by Suenram and Lovas. ... 

Carbenes, dioxirane preparation, 1132 Carbocations, antimalarial endoperoxides, 1309 Carbohydrate hydroperoxides, Mo-catalyzed olefin epoxidation, 432, 436 Carbohydrates, TBARS assay, 669 Carbonate esters, oxidative ozonolysis, 737, 738... 

Dioxiranes (32) are isomeric with carbonyl oxides (33), one of the peroxidic intermediates involved in the ozonolysis process.9 Dimethyldioxirane (DMDO) (31) epoxidizes the double bond of the protected galactal favoring the Oepoxide 8 with a selectivity of 20 1.10,11 You can use 31 likewise to transform an aldehyde into a carboxylic acid. 

The same authors published a detailed report on the calculations of the oxygen insertion into unactivated C-H bonds by dioxiranes using DFT theory and on comparison of the transition structures for stepwise routes via radical pairs with the concerted pathway <2003JOC811>. The articles dealing with the mechanism of OH formation from ozonolysis of isoprene and a- and /3-pinene provide DFT and ab initio calculation results also for the dioxirane formation <2001CPL(358)171, 2002JA2692, 2005JCP114308>. 

Only a few new reports of ring oxidations have appeared. One method uses dimethyldioxirane or methyl(trifluoro-methyl)dioxirane to convert 2,2-dimethyl-l,3-dioxolanes into 2-hydroxyketones under mild conditions (Equation 29) <1996TL115>. Ozonolysis of 1,3-dioxolanes has also been examined, and the primary reaction product of 2-alkyl-1,3-dioxolanes with ozone was identified as the 2-alkyl-l,3-dioxolan-2-ol <2002JA11260, 2004JA16093>. 

All carbonyl oxides proved to be highly photolabile, and on photolysis yield dioxiranes 3 or split off oxygen atoms to produce ketones. Oxygen atoms are also formed thermally from vibrationally excited 1. Thus, if the large exothermicity of the ozonolysis reaction is taken into account, 1 might be a source of O atoms and OH radicals in the troposphere. The role of dioxiranes has not yet been discussed in context with atmospheric chemistry, although the formation of these species in contrast to the isomeric carbonyl oxides - in ozone/alkene reactions has been unequivocally demonstrated [13]. 

The CBS-QB3, MCG3, RRKM/master equation, and transition-state theory (TST) calculations were made for a detailed analysis of cyclopropene ozonolysis, treating all possible conformers of all intermediates and transition structures (TSs). The TST rate constant indicated that approximately 90% of the reaction proceeded through the endo-TS. It was predicted that approximately one-third of activated syn Criegee intermediates (Cls) would cyclize to dioxiranes despite the fact that the barriers to dioxirane formation were higher than the barriers to the 1,4-hydrogen shift that would lead to vinyl hydroperoxides and "OH. This helped to reduce the predicted OH yield for cyclopropene ozonolysis to 44%. It was also predicted that approximately 20% of either the endo-primary ozonide (PO) or its syn Cl derivatives would isomerize to the exo-PO or anti Cls. ... 

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