Ozonides chromatography

Gas electron diffraction (GED) acyl peroxides, 702 peroxynitrates, 743-4 see also Electron diffraction Gas-hqiud chromatography (GLC) hydroperoxide determination, 684-5 ozonide determination, 719 Gas-phase addition, hydroperoxides, 157 Gas-phase epoxidation, alkenes, 58 gauche arrangement, acyclic organic peroxides, 102, 104-5 GED (gas electron diffraction), 743-4 Geminal regioselectivity... 

Ozonides and alkoxyhydroperoxides from 1-octene and ethyl 10-undecenoate were isolated by column chromatography and oxidized to acids, RCOOH, using (a) 02 at 95°C.,... 

Procedures. Chromatographic Purification of Ozonization Products. Ozonization products from ethyl 10-undecenoate and 1-octene were chromatographed on silica gel columns (Baker) and eluted with 15 or 25% ether in petroleum ether (b.p., 30°-60°). Fractions were examined by thin-layer chromatography (TLC) on silica gel G Chroma-gram sheet eluted with 40% ether in petroleum ether. For development of ozonide and peroxide spots, 3% KI in 1% aqueous acetic acid spray was better than iodine. The spots (of iodine) faded, but a permanent record was made by Xerox copying. Color of die spots varied from light brown (ozonide) to purple-brown (hydroperoxide), and the rate of development of this color was related to structure (diperoxide > hydroperoxide > ozonide). 2,4-Dinitrophenylhydrazine spray revealed aldehyde spots and also reacted with ozonides and hydroperoxides. Fractions were evaporated at room temperature or below in a rotary evaporator. 

The transformation of tetrasubstituted ethylenes into 1,2,4-trioxolanes may also be achieved if the ozonolysis is carried out in the presence of a foreign carbonyl compound as described in Section 4.33.3.4. With formaldehyde as added carbonyl compound, 3,3-disubstituted derivatives are obtained, whereas in the presence of excess ketone (e.g. by using the latter as solvent), the ozonolysis gives rise to tetrasubstituted 1,2,4-trioxolanes which are difficult to prepare by other methods. Reactions (163) -> (164) and (165) -> (166) provide two examples of this versatile 1,2,4-trioxolane synthesis. Unlike the parent system (2), alkyl- and/or aryl-substituted 1,2,4-trioxolanes generally are stable, non-explosive compounds. Mixtures of crossed ozonides (cf. Section 4.33.3.1.1) or of cis and trans isomers can be separated by thin layer, column or gas chromatography. The cis isomers of symmetrical 3,5-disubstituted 1,2,4-trioxolanes are meso forms, whereas the corresponding trans isomers represent racemates which in some cases have been resolved into their optical... 

Ozonides having one or two substituents at the trioxolane ring—in the latter case symmetrically or unsymmetrically—were prepared from the corresponding olefins by ozonization in pentane, usually at —78°C. The 3,5-disubstituted trioxolanes were separated into cis- and transisomers by crystallization or by column chromatography. 

After ozonation, the solvent usually was removed at 30 °C under rotation. The residue was either distilled in vacuo or crystallized or purified by column chromatography on silica gel. n-Pentane, with increasing amounts of ether (up to 1.5% ), served for the elution. Those mixtures of stereoisomeric ozonides which could not be separated pre-paratively were analyzed by their NMR spectra using a Varian A 60 spectrometer. The results are summarized in Tables II—V. More details can be found in Ref. 3. 

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. 

The configurations of the other ozonides are based on the assumption that the trans isomers have the lower dipole moments in comparison with the cis compounds. As a measure of the dipole moment the retention time in liquid phase or gas chromatography was used. The isomer with the lower retention time should be the trans compound. 

Fragmentation Products. All ozonides except for the tetrasubstituted ones are cleaved quantitatively by many solvents. While symmetrically disubstituted ozonides give one mole of acid and one mole of aldehyde as products, and trisubstituted ozonides yield one mole acid and one mole of a ketone, in the case of monosubstituted or unsymmetrically 3,5-disubstituted trioxolanes, two kinds of acids and two kinds of aldehydes are possible. The fragmentation products in these cases were treated with diazomethane, and the mixture of the methyl esters was analyzed by gas chromatography. The results are shown in Table VI. In all of these examples, the reactions go predominantly in one direction. When R and R are more similar, however, both kinds of reaction products would be expected in more nearly equal amounts. 

Ravandi, A., Kuksis, A., Myher, J. J. and Marai, L. (1995b) Determination of lipid ester ozonides and core aldehydes by high performance liquid chromatography with on-line mass spectrometry. J. Biochem. Biophys. Methods, 30, 271-85. 

Chromatography of ozonides. Unsaturated lipids react irreversibly with ozone. The ozonides are prepared before chromatography. 

Saturated compounds can be isolated unchanged after chromatography. The ozonides can be eluted from the adsorbent but the original unsaturated compounds cannot be recovered. 

---