Ozone, alkene reactions

Hull, L. A., I. C. Hisatsune, and J. Hekklen. Low-temperature infrared studies of simple alkene-ozone reactions. I. Amer. Chem. Soc. 94 4856-4864, 1972. 

In short, the Criegee intermediate from alkene-ozone reactions can contribute, in principle, to the gas-phase oxidation of S02. In practice, it is likely less important than reaction with OH. In addition, as we shall see, even the OH-SOz gas-phase reaction is, under many conditions, swamped out by reactions occurring in the liquid phase found in clouds and fogs. As a result, the CI-S02 reaction may contribute in some circumstances but is unlikely to be a major contributor to S02 oxidation as a whole. 

The main results of our investigations are (i) The first step in the alkene/ozone reaction is the formation of a 7i-complex with absorptions in the near UV or visible range, (ii) At 50-70 K this complex reacts to the primary ozonide (POZ) and, depending on substituents, traces of the secondary ozonide (SOZ). (iii) No carbonyl oxide was observed under any conditions used in our ozonolysis experiments, (iv) Some of the partially oxidized products formed are not in accordance with the Criegee mechanism and thus alternative mechanisms have to be considered. 

The reaction of ozone and alkenes is sufficiently fast that it can compete with other removal processes and provide sinks for both ozone and alkenes in the troposphere. While kinetic data for a series of alkene/ozone reactions have been reported, not much is known about details of the reaction mechanisms, the role that carbonyl O oxides play, and the role that free radicals play in these processes. Our laboratory experiments provide the spectroscopic data (both infrared and UV/visible) that are important for the spectroscopic identification of Criegee intermediates in the troposphere. In addition, we were able to characterize secondary partially oxidized products (aldehydes, peroxides etc.) that are produced during the gas-phase ozonolysis. These products might lead to a net increase of ozone, if oxygen atoms are formed during their decomposition. 

Certain aldehydes and ketones, when used as solvents, intercept and reduce a labile intermediate in the ozonolysis of olefins. The intermediate, which can be considered the progenitor of many other ozonolysis products, is formulated as the Staudinger molozonide, e.g. (577), and its reduction generates the corresponding dioxetan (578) with a Baeyer-Villiger oxidation of the aldehyde or ketone solvent. The dioxetan intermediate, normally cleaved to the carbonyl components, has now been isolated and characterized by using pinacolone as a solvent. Low-temperature infrared studies of simple alkene-ozone reactions have been made. ... 

Alkylaziridines can be stereospecifically deaminated to alkenes by reaction with m-chioroperbenzoic acid (70AG(E)374). The reaction and work-up are carried out in the dark to avoid isomerization of the cw-alkene, and the mechanism is thought to involve an initial oxidation to an amine oxide followed by a concerted elimination. Aziridine oxides have been generated by treating aziridines with ozone at low temperatures (71JA4082). Two... 

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... 

The overall ozonization reaction sequence provides an excellent means for locating the positions of double bonds in alkenes. The potentialities of the method may be illustrated by the difference in reaction products from the 1-and 2-butenes ... 

Kinetic data for ozonization reactions of a given number of alkenes in carbon tetrachloride at different temperatures are consistent with the presence of a pre-association equilibrium between the alkene and the ozone when electron-rich alkenes are used49. 

In the case of alkenes, the reaction with ozone starts on double bond C = C as a cycloaddition ... 

Reactions with ozone are competitive with the daytime OH radical reactions and the nighttime NO-, radial reactions as a tropospheric loss process for the alkenes. These reactions have been shown to proceed via initial O, addition to the olefinic double bond, followed by rapid decomposition of the resulting molozonide (Atkinson, 1990) ... 

Ethene, like other alkenes, reacts also with ozone in the atmosphere. The older work on ozone reactions has been reviewed by Leighton (1961) and by Bufalini and Altshuller (1965). More recent work has done much to clarify the principal reaction mechanisms involved. Criegee (1957, 1962, 1975), who had studied the ozonolysis of alkenes in solution, suggested that ozone adds to the C=C double bond, forming an unstable intermediate, which then decomposes toward a carbonyl compound and a zwitterion fragment, for example ... 

The analysis of organic compounds by ozone reaction GC was described in ref. 268. Tlie double-bond analyser was based on the chemical reaction between ozone and alkene after separation, the decrease in ozone concentration being measured by UV absorption. The technique simplified the identification of peaks, increased the effectiveness of the analysis and eliminated the overlapping of peaks. 

This type of dipolar addition reaction was introduced in chapter 3 in connection with ozonolysis (sec. 3.7.B), as well as permanganate (sec. 3.5.A),346 and osmium (sec. 3.5.B) oxidation of alkenes. Ozone is a classical example of a dipolar molecule (see canonical forms of 424 +0—O—0 and 0—O—0+). Fleming showed that the HOMO/LUMO orbitals of ozone interact with those of ethene (as shown in Figure 11.21).347... 

Ozonation of Alkynes. Reactions of alkynes with ozone afford either carboxylic acids or, if reductive procedures are used, a-dicarbony 1 compounds. For the production of carboxylic acids, MeOH has been shown to be superior to CH2CI2 as reaction solvent. As with alkenes, a number of reducing agents can be used to produce a-dicarbonyl compounds. An easy option which results in high yields of a-dicarbonyl compounds involves the addition of Tetracyanoethylene directly to an ozonation reaction mixture as an in situ reducing agent (eq 16). ... 

Although ozone-alkene reactions were not specified in the original objectives of LACTOZ they constitute a loss process for ozone and are important for degradation of unsaturated hydrocarbons, in particular alkenes with multiple double bonds and complex structures, such as are found in the biogenic hydrocarbons. Emphasis in LACTOZ has been on the rates and mechanisms under atmospheric conditions. These studies led to downward revision of the rate constants of the O3 alkene reactions, due to complications arising in many earlier investigations from secondary reactions of radicals produced in the primary step. Some important hitherto unknown aspects of ozone reactions, such as the formation of peroxides and their dependence on the water vapour concentrations, have been discovered in LACTOZ. 

The mechanism of the ozonolysis reaction of alkenes has been investigated in the gas phase and solid state using matrix isolation spectroscopy. While alkene/ozone 7C-complexes and the primary ozonides are readily observed by IR und UV/vis spectroscopy, there is no direct spectroscopic evidence for the Criegee intermediate (carbonyl O oxide) in these reactions. However, these elusive species can be synthesized and characterized via the carbene/oxygen route. Comparison of experimental and calculated spectroscopic data allows for the prediction of the spectroscopic properties of carbonyl oxides which are not accessible by this method. 

Ozone plays a major role in the degradation of unsaturated VOCs in the troposphere, especially during night-time. The rate constants of the ozonolysis of a variety of alkenes have been reported [1]. However, in most instances the fate of the primary products of the ozonolysis is unknown, although the secondary reaction products are of crucial importance for the overall understanding of the alkene/ozone chemistry. The classical Criegee mechanism of the ozonolysis reaction involves the primary ozonide (POZ, 1,2,3-trioxolane), which cleaves to the Criegee intermediate (carbonyl O oxide) and a carbonyl compound [2, 3]. The secondary ozonide (SOZ, 1,2,4-trioxolane) is formed from these components in a [l,3]-dipolar cycloaddition reaction. 

Mechanistic studies of ozone reactions with alkenes,... 

Alkene Oxidation Reactions. The reaction of triethylsilane with ozone and use of the intermediate triethylsilyl hydrotrioxide in oxidation reactions have been described. Initial oxidation reactions reported included the formation of the 9,10-endoperoxide from 9,10-dimethylanthracene (eq 1), and an allyUc hydroperoxide from 2,3-dimethyl-2-butene (eq 2). Researchers also observed a near-IR emission from triethylsilyl hydrotrioxide as it decomposed at —60°C, consistent with generation of singlet oxygen. Other workers have characterized triethylsilyl hydrotrioxide by NMR spectroscopy and and measured the kinetics of its decomposition in deuterated acetone. ... 

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