Ozonides isolation

The highly reactive carbonyl oxide could be trapped by added carbonyl com-pounds to form normal ozonides. Isolation of dimeric (77) and polymeric... 

Excess of ozone should be avoided since further oxidation may occur to oxozonides or perozonides. ) The ozonides are usually not isolated since they are generally viscid oils or glasses, sometimes with violently explosive properties particularly on warming. They can, however, be completely... 

Aldehydes are easily oxidized to carboxylic acids under conditions of ozonide hydroly SIS When one wishes to isolate the aldehyde itself a reducing agent such as zinc is included during the hydrolysis step Zinc reduces the ozonide and reacts with any oxi dants present (excess ozone and hydrogen peroxide) to prevent them from oxidizing any aldehyde formed An alternative more modem technique follows ozone treatment of the alkene m methanol with reduction by dimethyl sulfide (CH3SCH3)... 

This cleavage reaction is more often seen in structural analysis than in synthesis The substitution pattern around a dou ble bond is revealed by identifying the carbonyl containing compounds that make up the product Hydrolysis of the ozonide intermediate in the presence of zinc (reductive workup) permits aide hyde products to be isolated without further oxidation... 

Formation of Ozonides. Although the patent compound, HO3, is too unstable to be isolated, metal and nonmetal ozonides have been... 

Commercially, pure ozonides generally are not isolated or handled because of the explosive nature of lower molecular weight species. Ozonides can be hydrolyzed or reduced (eg, by Zn/CH COOH) to aldehydes and/or ketones. Hydrolysis of the cycHc bisperoxide (8) gives similar products. Catalytic (Pt/excess H2) or hydride (eg, LiAlH reduction of (7) provides alcohols. Oxidation (O2, H2O2, peracids) leads to ketones and/or carboxyUc acids. Ozonides also can be catalyticaHy converted to amines by NH and H2. Reaction with an alcohol and anhydrous HCl gives carboxyUc esters. 

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. 

Griesbaum K, V Miclaus, IC Jung (1998) Isolation of ozonides from gas-phase ozonolysis of terpenes. Environ Sci Technol 32 647-649. 

The zwitterion (59) is thereby prevented from reacting with the ketone (58) to form the ozonide in the normal way, and both (58) and (60) may now be isolated and identified. In preparative ozonolysis it is important to decompose the ozonide (57a) by a suitable reductive process, as otherwise H202 is produced (on decomposition of the ozonide with H20, for example) which can further oxidise sensitive carbonyl compounds, e.g. aldehydes— carboxylic acids. 

Ozonides are not usually isolated but are reduced directly by treatment with znic and acetic acid (HOAc). 

When ozonolysis is done in alcoholic solvents, the carbonyl oxide fragmentation product can be trapped as an a-hydroperoxy ether.146 Recombination to the ozonide is then prevented, and the carbonyl compound formed in the fragmentation step can also be isolated. If the reaction mixture is treated with dimethyl sulfide, the hydroperoxide is reduced and the second carbonyl compound is also formed in good yield.147 This procedure prevents oxidation of the aldehyde by the peroxidic compounds present at the conclusion of ozonolysis. 

Different isomers of C qO have been prepared by photooxygenation [48], by MCPBA-oxidation [48], by ozonolysis [49] or they were extracted from fullerene soot [11, 50]. Isolation from fullerene soot and analysis of the product of photooxygenation and thermal ozonolysis yields only [6,6]-closed epoxide structures. As already observed for CgoO, ozonolysis and subsequent photolysis of the ozonide C7QO3 gives different [5,6]-open oxidoannulene structures [49]. 

A detailed assignment of the IR absorption frequencies of 1,2,4-trioxolane (1) in solid argon was achieved by comparison with the spectra of various isotopically substituted species <82JPC3154>. Similarly, for a series of substituted 1,2,4-trioxolanes, characteristic IR bands obtained via matrix isolation were assigned and compared with those of 1,2,4-trioxolane (1) (ethylene ozonide) (Table 7) <82JPC4548>. The spectra of cis- and trani-1,2,4-trioxolanes indicate that the cis isomer has characteristic absorptions in the range 820-855 cm with the trans isomer at 1320-1360 cm . 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

Trioxolane (1) has only been prepared by the ozonolysis of ethylene. The rearrangement of the primary ozonide occurs above — 100°C to give 1,2,4-trioxolane as a colorless, explosive liquid <42LA(553)187>. 1,2,4-Trithiolane (2) is still best prepared by a classical reaction of Na2S2.5 with excess dichloromethane. Some 1,2,4,5-tetrathiolane is also produced, but (2) can be isolated as a pale-yellow distillable liquid. It is best kept stored under inert atmosphere below 0°C to avoid polymerization <67CPB988>. Parent compounds (3)-(6) are not known and the 1- and 4-5-oxides for 1,2,4-trithiolane have been mentioned previously (see Section 4.16.5.2.3). 

Ozonolysis is generally carried out in solution as part of a synthetic route. Many 1,2,4-trioxolanes are isolated because of their unusual stability. In deliberate preparations of 1,2,4-trioxolanes, reactions in solution may not always be the most efficient process. Several ozonides can be prepared by dry ozonolysis where the alkene is reacted without solvent, for example the highly stable perfluoroalkyl 1,2,4-trioxolane (139) was obtained by heating the alkene (138) to 100°C in the presence of ozone (Equation (24)) <85TL2889>. 

Several stable triterpenoid natural products containing 1,2,4-trioxolanes have been characterized, for example adian-5-ene ozonide (175) isolated from the fern Adiantum monochlamys <90CPB79,... 

These observations were applied by Dimitrov, Hesse and coworkers. On stndying ozonization of a series of allylic and homoallylic alcohols prepared from (+) camphor and (—) fenchone, they were able to isolate a certain number of ozonides and to obtain the O NMR spectrum of the diastereomeric mixture of one of them, i.e. derivative 15, whose structure and O NMR chemical shifts (5, ppm) are shown below. 

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