Ozonides Subject

Cracking of the surface of stretched rubber exposed to ozone. The ozone will only crack unsaturated (i.e., containing double bonds) rubbers when they are subjected to tensile strain, the cracks are at 90° to the direction of the strain. Ozonide... 

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 . ... 

The ozonides of choline and ethanolamine phosphatides and triglycerides can be subjected to reduction with triphenylphosphine to yield the corresponding core aldehydes, and further derivatized to the 2,4-dinitrophenylhydrazones (DNP). The core aldehydes and their DNP derivatives can be separated by HPLC and characterized by various techniques, including EI-MS and TS-MS of positive and negative ions . See also Section VHI.E. 

Several polymethyl-1,2-diphenylcyclobutenes, 82a-c, subjected to DCA-photo-oxidation in acetonitrile, afford 1,4-diketones 83a-c together with moderate amounts of the ozonides 85a-c, apparently formed from oxiranes, 84a-c, produced in the primary step ... 

The chemistry of the ozonide radical anion has been discussed in Czapski s review (88), but the chemistry is complex, and the interested reader should consult more recent sources (282). The potential of the 03/03 couple has not been the subject of repeated scrutiny. Klaning et al. recently measured it by investigating reaction 10 (182). Their value of 1.01 V leads to AfG° = 77 kJ/mol for 03 these results are probably fairly accurate because they confirm the potential of the OH/OH" couple. There is considerable uncertainty expressed in Czapski s review concerning the pKa of H03 (88) on the basis of chemical analogy he estimated a pKa of — 2. In a recent investigation it was asserted that H03 has a pK of 6.15, although it splits into OH and oxygen before it has time to dissociate into 03 (60). Subsequently the pKa was corrected to 8.2 + 0.1 (61). It is prudent to await confirmation of these results. 

Carboxylic acids are produced in good yields if the ozonide, formed when ozone reacts with a double bond as in equation (6), is subjected to oxidative hydrolysis. Although a variety of oxidants e.g. chromic acid, permanganate ion and peroxy acids) have been used for this puipose, hydrogen peroxide is most commonly employed. 

The mechanism of the reaction of ozone with double bonds (equation 68) is very complex and still subject to arguments. An alkene and ozone may first form a it complex (a), which forms a a complex (b), a molo-zonide (c), or both. The molozonide may change to a dipolar ion (d), which breaks down with the fission of the carbon-carbon bond to a carbonyl compound and another dipolar ion (e). The two species recombine to give the ultimate product, ozonide (f) (1,3,4-trioxolane, also known as 1,3,4-trioxacyclopentane) [76], The temporary presence of the carbonyl com-... 

T he reaction of ozone with olefins usually results in cleavage of the double bond and the formation of aldehydes, ketones, and/or carboxylic acids, depending upon the reaction conditions and the structures involved. For aldehydes, the intermediate ozonides are ordinarily treated with a mild reducing agent—for example, hydrogen or zinc—or subjected to neutral hydrolysis. Yields in excess of 70% are exceptional for the reduction methods, while hydrolysis gives considerably lower yields. 

In particular the autoxidation of benzaldehyde was investigated. Its choice as the initial subject for study was unfortunate, as the use of an impure sample of perbenzoic acid for determination of its absorption spectrum, not previously recorded, led to erroneous conclusions. These were later rectified after taking new measurements on a pure crystalline sample of the peracid (12). For the present study the two main bands at 1728 to 1730 and at 1270 cm.- are to be borne in mind. These bands made possible a demonstration of the acceleration of the autoxidation due to ozone and the influence of such acceleration in ozonide formation. Three spectral series (Figures 1, 2, and 3), obtained in collaboration with E. Dallwigk, are discussed below. 

One process (16) subjects them to light from a neon lamp ranging from yellow to orange in color, in the presence of oxygen. Another (20) subjects them to ultra-violet rays after addition of a small amount of hydrogen peroxide, inorganic and organic peroxide, or ozonide. 

Elemol (79) was subjected to ozonization at -78°C. The resulting ozonide on treatment with Me2S yielded hydroxyl ketone (80). Its acetate (81) was subjected to Lemieux-Johnson oxidation afforded acetate (82) which was cyclized to indenone (83) with methanolic sodium hydroxide solution. Its sodium enolate in a mixture of tetrahydrofuran, dimethylformamide and t-BuOH was oxidized with oxygen in presence of triethylphosphite to obtain hydroxyl ketone (84). This on treatment with... 

Scheme 7 Ozonization of alcohol (79) followed by treatment of the ozonide with Me2S afforded hydroxy ketones (80), whose acetate derivatives was converted to indenone (83). Hydroxy ketone (84), prepared from (83) was converted to compound (85), whose acetate on oxidation gave diol (87). Its transformation to butenolide (88) was easily carried out. This on oxidation and reduction produced hydroxy phytuberin lactone (89), which was converted to its sulfonyl derivative. Reductive removal of the sulfonate group yielded the cyclopropane derivative (91), which on subjection to reductive cleavage with lithium in liq. NH3 yielded phyberin lactone (92) and deacetyl phytuberin lactone (93)...

The ozonolysis reaction has been the subject of considerable mechanistic study. It is likely that in most cases the reaction proceeds by breakdown of the 1,3-dipolar cycloaddition product to a carbonyl oxide 99 and an aldehyde (or ketone) (5.99). The fate of the carbonyl oxide depends on the solvent and on its structure and the structure of the carbonyl compound. In an inert (non-participating) solvent, the carbonyl compound may react with the carbonyl oxide to form an ozonide 100 otherwise the carbonyl oxide may dimerize to the peroxide 101 or give ill-defined polymers. In nucleophilic solvents such as methanol or acetic acid, hydroperoxides of the type 102 are formed. 

Use in Solid Phase Synthesis. Solid phase symthesis offers the ability to perform transformations that involve little to no workup and purification. Ozone, possessing the same properties in certain cases, seems well suited to solid phase synthesis. Undec-lO-enoic acid was coupled to merrifield resin under standard conditions using 1,3-dicyclohexylcarbodiimide (DCC). The terminal olefin was then subjected to ozonolysis at low temperature in CH2CI2. The intermediate secondary ozonide could be converted into an alcohol, aldehyde, or carboxylic acid depending on the workup conditions. 

When appreciable concentrations of carbonyl compounds are present before complete formation of ozonide, crossed ozonides are formed. This occurs when the added carbonyl compound traps the zwitterion formed in the cleavage step. When c -stilbene is subjected to ozonolysis in the presence of 0-labeled benzal-dehyde, the label is incorporated into the ether rather than the peroxide portion of the ozonide ... 

Alternatively, ozonides (Section 8.17B) can be subjected to an oxidative workup that yields carboxylic acids ... 

The catalytic properties of Co in the hydrocarbon oxidation have been the subject of intensive investigations [107], It has been established that during the cumene-AcOH ozonolysis in 1 1 (v v) in the presence of Co(AcO)2 the oxidation reaction is accelerated (Fig. 17).In contrast to the noncatalysed process in the catalyzed by transition metal salts the ozonolysis is characterized by 1) absence of ozonides formation that is indicative of the absence of ozone interaction with the phenyl ring and 2) the main product is DMPC, the accumulation rate of which proportional to the concentration of Co after the 10 min. The initial rates of CHP formation do not vary with the changes in Co + but after the 15 min the rates increase with [Co ]. It can be seen from Table 9 that if we assume the ozonolysis of pure cumene as a reference then the addition of AcOH results in autoretardation of the oxidation rate and to reduction of the products yield. The ratio [IP]/[03 reaches value of 6.9. 

---