Stilbene ozonide

Interaction of alkenes with ozonised oxygen tends to give several types of products or their polymers, some of which show more pronounced explosive tendencies than others [1]. The cyclic ge/n-diperoxides are more explosive than the true ozonides [2], It has been calculated that ozonisation of the endothermic /rara-stilbene (AH°f +135.4 kJ/mol, 0.78 kJ/g) would give, in the event of decomposition of the unstable ozonide, an exothermic release of 1.41 kJ/g which would attain an adiabatic decomposition temperature approaching 750°C with a 27-fold pressure increase in a closed vessel [3],... 

The second ozonide is that from fraw -stilbene, i.e. the 3,5-diphenyl trioxolane derivative. The ozonation experiment was done on both the cis and trans olefins resulting in reaction enthalpies of —471.5 and —428.9 kJmoU, respectively. The difference between these two values is ca 43 kJ moU, which is close to the difference between the two olefins enthalpies of formation (one as liquid and the other as solid), 46 2 kJ moU. This result vindicates the original authors suggestion of using the ozonation enthalpies as a method of determining the difference between enthalpies of formation of a Z/ pair of olefins. 

Qolutions of stilbene ozonides in methanol slowly decompose at room temperature with the formation of benzoic acid and benzaldehyde. Other ozonides show similar behavior. However, the reaction rates differ from solvent to solvent and depend on the constitution and configuration of the ozonide. Therefore, we decided to investigate these reactions more carefully. Many new ozonides—especially those with one or more aromatic substituents—had to be prepared, and their configurations had to be established. 

Other new ozonides include those of acenaphthylene and 3,4-di-chloro-3,4-dimethyl-cyclobut-l-ene. They are the cyclic analogs of cis-stilbene ozonide and l,4-dichloro-but-2-ene ozonide, respectively. Altogether, more than 45 ozonides were investigated. 

Configuration of cis-trans Isomeric Ozonides. In symmetrically di-substituted trioxolanes, the cis isomer is a meso and the trans isomer is a racemic form. Therefore, resolution into antipodes makes it possible to determine the configuration. In 1966, Loan, Murray, and Story (4) were able to obtain an optically active form of one of the diisopropyl-trioxolanes, proving it to be the trans isomer. Their method—partial decomposition of the ozonide by brucine—could not be applied to the stilbene ozonides. 

Chromatography of a benzene solution of the low melting stilbene ozonide (mp 92°C) on finely divided cellulose-2 1/2-acetate, however, yielded fractions of the ozonide with specific rotation at 360 nm of -j-8.94° and —20.45°, respectively (5). This isomer, therefore, is the trans compound. Under the same conditions, the higher melting ozonide (mp 100°C) gave no fraction with optical activity, in agreement with its cis configuration. 

Unfortunately, the dependence of the rates on pH cannot be measured by our method since acidimetric titrations are not possible in buffered solutions. However, in weakly acidic and neutral solutions, there cannot be much influence because otherwise no rate constants could have been obtained. In alkaline solution, on the other hand, a base induced fragmentation occurs, which is faster by some powers of 10 than the solvent fragmentation. Thus, in 0.025N methanolic NaOH at 0°C, the half lifetime of stilbene ozonide is only 2 minutes. 

Aldozonides are more sensitive towards alkalis than towards acids. The base evidently attacks the a-hydrogen atom of the ozonide. An example of this is probably the decomposition of stilbene ozonide to give benzoic acid and benzaldehyde [Eq. (10)].120... 

To satisfy the yields of aromatic aldehydes obtained (Table I), rates ki and must be considerably greater than the heterolysis rate, 3. This seems reasonable because equilibration of V and VII when aldehyde is removed should occur readily in the aromatic series where Ri can offer substantial resonance stabilization to the transition state, VI, by enhancing the cationic character of the carbonyl carbon. In Briner s early work (1,2) on the hydrolysis of stilbene and isoeugenol ozonides, advantage was not taken of these equilibria and rate differences. As a consequence almost half of the final cleavage products after extensive hydrolytic treatment without aldehyde removal were carboxylic acids, IX. 

Clearly in the case of the stilbenes, if the above proposal mechanisms are correct, half of the aldehydes produced must have resulted from the hydrolysis of hydroperoxide intermediates. With the unsymmetrical olefins, styrene, anethole, isosafrole, estragole, and 1-dodecene, this may not be the case. If cleavage of the primary ozonide is unimolecular, then the inductive and resonance contributions of substituents Ri and R2 in X should determine the direction of cleavage. Thus, if E-i is more capa-... 

Criegee and others (23) published new results, which led to the resumption of these investigations. He pointed out that the infrared spectra of really pure ozonides contained no bands in the range of spectral frequencies of CO group vibrations. This was verified in these laboratories with a sample of pure fmns-stilbene ozonide obtained from Criegee. 

Calculated values in parentheses. b Plus 9% stilbene ozonide (cis/trans 4/6). 

The mechanism is thought to involve oxidation of the biphenyl by DCA to form a radical cation. A quantitative yield of ozonide is obtained when electron-rich epoxides, eg. trans-4,4 -dimethoxystilbene oxide,are irradiated in MeCN containing DCA under an 0 stream1 1. Less electron-rich substrates eg. stilbene oxide do not product ozonides under these conditions. 

Such a sequence explains, for instance, the formation of the same secondary ozonide from cis or trani-stilbene, and the isolation of the secondary ozonide of isobutene from the ozonolysis of 2,3-dimethyl-2-butene in the presence of formaldehyde -, viz-... 

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 ... 

Reactivity and Incompatibility Ozone is a powerful oxidant and can react explosively with readily oxidizable substances and reducing agents. Explosions can occur when ozone is exposed to bromine, hydrogen bromide, hydrogen iodide, nitrogen oxides, lithium aluminum hydride, metal hydrides, hydrazine, alkyl metals, stilbene, ammonia, arsine, and phosphine. Ozone reacts with alkenes and other unsaturated organic compounds to form ozonides, many of which are highly unstable and explosive. Ozone combines with many aromatic compounds and ethers to form shock-sensitive and explosive products. 

Phenylcyclopentene ozonide reacted similarly with chlorosulfonic acid, although the same ozonide reacted stereoselectively with antimony pentachloride to yield the cis tetraoxan (55%). The conversion of ozonides to tetraoxans by treatment with catalytic amounts of chlorosulfonic acid appears to be a fairly general reaction thus l,2-diphenylethylene(stilbene) ozonide 475 yields the corresponding tetraoxan 476 41% (Equation 152). 

The reaction of a mixture of two kinds of ozonides in the presence of an acid catalyst affords the crossed 2,3,5,6,ll-pentaoxabicyclo[5.3.1]imdecane derivative. For instance, a mixture of 3-phenylindene ozonide 485 and stilbene ozonide 475 reacted with chlorosulfonic acid (0.03 equivalents) to give the crossed 2,3,5,6,11-pentaoxabicyclo[5.3.1]undecane 486, 25%, together with the tetraoxa compound 476, 7%, a cyclic peroxide (Equation 155). ... 

Chlorosulfonic acid catalyses several interesting rearrangements of ozonides, which probably involve heterolytic fusion of the carbon-oxygen bond of the peroxide bridge. For instance, methylcyclopentene ozonide, on treatment with chlorosulfonic acid (0.3 equivalents) in dichloromethane at RT, rearranged to form a trans tetraoxan (see Chapter 4, p 125). Stilbene ozonide with chlorosulfonic acid under similar conditions, also afforded the corresponding tetraoxan and this appears a fairly general reaction. 

Schaap, A. R, Siddiqui, S., Gagnon, S. D., and Lopez, L., Stereoselective formation of cis-stilbene ozonide from the cosensitized electron-transfer photooxygenation of cis- and trans-2,3-dipheny-loxiranes, /. Am. Chem. Soc., 105, 5149,1983. 

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