Ozonolysis alkenes, ozone

Ozonide A compound formed by the reaction of ozone with an alkene. Ozonolysis Ozone-induced cleavage of a carbon-carbon double or triple bond. 

The oxidation of an alkene with ozone followed by treatment with zinc in the presence of acid gives aldehydes and/or ketones. The reaction breaks the carbon-carbon double bond and changes each of carbon atoms of the C=C to a carbonyl group. Figure 10-7 shows an excimple of the ozonolysis of an alkene. 

The reaction of alkenes with ozone constitutes an important method of cleaving carbon-carbon double bonds.138 Application of low-temperature spectroscopic techniques has provided information about the rather unstable species that are intermediates in the ozonolysis process. These studies, along with isotope labeling results, have provided an understanding of the reaction mechanism.139 The two key intermediates in ozonolysis are the 1,2,3-trioxolane, or initial ozonide, and the 1,2,4-trioxolane, or ozonide. The first step of the reaction is a cycloaddition to give the 1,2,3-trioxolane. This is followed by a fragmentation and recombination to give the isomeric 1,2,4-trioxolane. The first step is a... 

The formation of 1,2,3-trioxolanes from an alkene and ozone is the first step in the ozonolysis reaction, which is widely used in synthesis to convert alkenes to aldehydes or carboxylic acids. No instances of double bond migration during ozonolysis are known (since the first step is a cyclo-... 

Oxidation of alkenes with ozone followed by cleavage of the resulting ozonides to carbonyl compounds is widely used for the determination of structure of unsaturated compounds. The ozonolysis technique is described in detail in Section 2.17.4, p. 103. 

There are six possible five-membered monocycles 1-6 containing three oxygen or sulfur atoms in the 1,2,3-positions <1996CHEC-II(4)545>. 1,2,3-Trioxolane 1 is the parent compound of the so-called primary ozonides, the primary reaction products in the reaction of alkenes with ozone. They are extremely unstable and rearrange to the more stable ozonides (1,2,4-trioxolanes). This rearrangement represents a key step in the reaction of ozonolysis. However, the parent compound 1 and a few derivatives have been characterized at low temperatures (see Section 6.05.10.1). 1,2,3-Trithiolanes have been synthesized (Section 6.05.10.3) some of them undergo slow decomposition at room temperature. Derivatives of 1,2,3-dioxathiolane 3 are unknown, and the other heterocycles of the mixed types 4-6 are known only in the oxidized forms, mostly as -oxides and J -dioxides, and also A-imino and A-thiono derivatives <1996CHEC-II(4)545>. The A-oxides and AA -dioxides of... 

As it is well known, acyloxy, alkoxy, or phenoxy groups connected to sp2-hybridized carbon atoms in alkenes or aromatics are unreactive to nucleophilic substitution. However, after alkene ozonolysis such groups become attached to sp3-hybridized carbon atoms and become reactive. It was shown <1989TL1511> that such substitutions have to be carried out at 40 °C when they compete with thermolytic reactions of the ozonides, lowering the yields. However, if 2,3-dichloropropene and as- or /ra/rt-1,2,4-trichloro-2-butene are ozonized, one obtains stable ozonides 68a-70... 

The mechanism proposed by Criegee for the ozonolysis of alkenes <1975AGE745> considers an initial it-complex between the alkene and ozone which decays via a 1,3-dipolar cycloaddition into a 1,2,3-trioxolane or primary ozonide, known also as the molozonide . These compounds are unstable, even at low temperatures, and due to cycloreversion decompose into a carbonyl fragment and a CO, which may recombine by another 1,3-dipolar cycloaddition step to form the more stable 1,2,4-trioxolane ( secondary ozonide or final ozonide (see also Section 6.06.2). 

The cleavage of alkenes by ozone, usually to give carbonyl compounds as products, is a reaction which has been widely exploited in synthesis and on which a great deal of mechanistic work has been carried out. Reviews of this chemistry are available.The ozonolysis usually leads to the formation of one of two distinct types of peroxidic product (Scheme 34) the cyclic peroxides (53), which are formed in nonnucleophilic solvents, and acyclic hydroperoxides, such as (54X which are formed in the... 

Aldehydes can be converted to peroxy acids via ozonation in methyl or ethyl acetate, or to methyl esters via ozonation in 10% methanolic KOH (eq 36). Ethyl esters can be produced analogously, but the use of higher alcohols results in low KOH solubility and poor conversion. This problem can be overcome by adding the aldehyde to a solution of lithium alkoxide in THE at —78 °C and treating this mixture with ozone (eq 37). Additionally, the direct preparation of methyl esters can be accomplished via alkene ozonolysis in methanolic NaOH or by addition of NaOMe to a MeOH-CH2Cl2 ozonolysis solvent system. ... 

Ozonolysis is the oxidation of alkenes with ozone to give carbonyl compounds. 

The reaction of ozone with an aromatic compound is considerably slower than the reaction with an alkene. Complete ozonolysis of one mole of benzene with workup under non-oxidative conditions will yield three moles of glyoxal. The selective ozonolysis of particular bonds in appropriate aromatic compounds is used in organic synthesis, for example in the synthesis of a substituted biphenyl 8 from phenanthrene 7 ... 

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. 

Alkenes with at least one vinjdic hydrogen undergo oxidative cleavage when treated with ozone, yielding aldehydes (Section 7.9). If the ozonolysis reaction is carried out on a cyclic alkene, a dicarbonyl compound results. 

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

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