Alkenes with Ozone

The reaction of ozone with alkenes proceeds via addition to the double bond giving a short lived energy-rich ozonide, which decomposes via C - C bond scission to give carbonyl compounds and biradical species known as Criegee biradicals ... 

Criegee biradicals formed in the reaction of ozone with alkenes carry significant internal excitation and the majority of them decompose before they can be collisionally stabilized. The biradicals are sufficiently excited that many different rearrangements and decomposition pathways are energetically allowed. For example, in the case of the [CH3C( )H00( )] species formed during propene oxidation the IUPAC panel has recommended the following channels (and yields) [24] ... 

Channel Eq. 30b is of considerable importance as it produces OH radicals. The OH radical yield varies between 10 and 100% depending on the particular alkene [8,59]. Although it has been known for many years that OH radicals are produced in the reaction of ozone with alkenes [60] it has only recently been recognized that this could be an important nighttime source of OH radicals in the atmosphere. Channel Eq. 30a gives a stabilized biradical. The atmospheric fate of stabilized biradicals is dominated by reaction with water vapor, which proceeds predominately to give carboxylic acids, e.g.,... 

In summary, the reaction of ozone with alkenes is important in the atmospheric degradation of alkenes. In all cases the reaction leads to rupture of the > C = C < double bond. The double bond is replaced by a carbonyl group on one side and a Criegee biradical on the other. The Criegee biradical is formed energetically excited and decomposes by a variety of different routes to give a complex mixture of oxygenated products (mainly carbonyls). 

Table 5 Range of OH yields from the reaction of ozone with alkenes...

The reaction of ozone with alkenes is one of the most useful 1,3-dipolar cycloadditions. Ozone undergoes [3 + 2] cycloaddition to the alkene to give a... 

In an attempt to determine the atmospheric oxidation processes that would result in an arene oxide functional group in PAHs, Murray and Kong (1994) studied the reaction of particle-bound PAHs with oxidants derived from the reactions of ozone with alkenes. Phenanthrene and pyrene were converted to arene oxides under these simulated atmospheric conditions. Control experiments indicated that the oxidant responsible for the transformation was not ozone, but a product of the reaction of ozone with tetramethylethylene (TME), probably the carbonyl oxide or the dioxirane derived from TME. 

Reactions involving a five-membered transition state are even more favoured on entropy grounds, although there is some angle strain in the transition state and the products. The first step in the reaction of ozone with alkenes is a reaction of this type (7.5), as is the reaction of diazomethane with alkenes such as methyl acrylate (methyl propenoate) (reaction 7.6). In each case, six p-type electrons are involved, a Hiickel number, so the reactions will be favoured as long as the reactions are entirely suprafacial. The movement of three pairs of electrons (six in total) is shown by the curved arrows, and corresponds to the bonds broken and formed during these two reactions. 

The reaction of ozone with alkenes is one of the most useful 1,3-dipolar cycloadditions. Ozone undergoes [3 -I- 2] cycloaddition to the alkene to give a 1,2,3-trioxolane, which immediately decomposes by a [3 -I- 2] retro-cycloaddition to give a carbonyl oxide and an aldehyde. When the ozonolysis is carried out in the presence of an alcohol, the alcohol adds to the carbonyl oxide to give a hydroperoxide acetal. In the absence of alcohol, though, the carbonyl oxide undergoes another [3 -b 2] cycloaddition with the aldehyde to give a 1,2,4-trioxolane. 

TABLE 6.21 Rate Constants for the Reaction of Hydroxyl and Nitrate Radicals and Ozone with Alkenes... 

The reaction of ozone with alkenes produces OH and other radicals. Work in LACTOZ has provided quantitative data for the yield of OH for a variety of alkenes, including biogenic hydrocarbons. Yields of around 50 % were obtained for the reaction of ozone with typical alkenes, making this a source of atmospheric free radicals, which is especially significant at night-time when photolytic sources are absent. 

As part of an investigation into the reaction of ozone with alkenes, the temperature dependence of the rate constants for the reaction of O3 with a series of cycloalkenes and the formation yields for OH radicals in these reactions have been obtained in the present work. 

Kinetic Studies on the Reaction of Ozone with Alkenes and Haloakenes,... 

The value of E° in eq. 16.10 refers to pH = 0 (see Box 8.1), and at higher pH, E becomes less positive +1.65 V at pH = 7, and +1.24 V at pH = 14. The presence of high concentrations of alkali stabilizes O3 both thermodynamically and kinetically. Ozone is much more reactive than O2 (hence the use of O3 in water purification, see Box 14.1). Reactions 16.11-16.13 typify this high reactivity, as does the reaction of ozone with alkenes to give ozonides. 

By the same approximate technique that was used to obtain activation energies, the rates for reaction of ozone were determined for a variety of types of organic species. Table II gives data of this type. It can be seen that the relative rates of reaction of ozone with alkenes ROOH alkanes is approxiiaately in the ratios of 10 10 10. ... 

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