Ozone cycloalkenes

Hatakeyama, S., Ohno, M., Weng, J., Takagi, H., and Akimoto, H. Mechanism for the formation of gaseous and particulate products from ozone-cycloalkene reactions in air. Environ. Scl. Technol., 21(l) 52-57, 1987. 

In order to determine the OH formation yields from the reaction of O3 with the cycloalkenes two different sets of experiments were carried out. Firstly, the loss of O3 and the cycloalkene were monitored in experiments where [O3]o and [cycloalkeneJo were in the range 1 to 6 ppm. The results provided values for the stoichiometry of the reactions, A[cycloalkene] / A[03]. In a second series of experiments, sufficient cyclohexane was added to the reaction system in order to scavenge OH radicals formed in the ozone-cycloalkene reactions. In these experiments the loss of cycloalkene, O3 and the yield of cyclohexanone, formed by the reaction of OH with cyclohexane were monitored. In order to determine the yield of cyclohexanone resulting from the reaction of OH with cyclohexane under the reaction conditions employed for the 03/cycloalkene/cyclohexane experiments, a series of experiments was carried out in which the cyclohexane concentrations employed were such that the OH radicals react both with the cycloalkene and cyclohexane. Under these conditions the loss of cyclohexane due to reaction with OH and the formation of cyclohexanone could be determined. The results from these studies showed that A[cyclohexanone] / A[cyclohexane] = 0.26 0.04 for all the alkenes investigated. 

Atkinson, R., Aschmann, S.M., Carter, W.L., Pitts, Jr., J.N. (1983) Effects of ring strain on gas-phase rate constants. 1. Ozone reactions with cycloalkenes. Int. J. Chem. Kinet. 15, 721-731. 

It should be noted that while the mechanism outlined in this section describes the overall features of 0,-alkene chemistry, there are also other minor paths as well. For example, small yields of epoxides that appear to be formed in the primary reaction have been observed as products of the reactions of some dienes and cycloalkenes (e.g., see Paulson et al., 1992b and Atkinson et al., 1994a, 1994b). The reader should consult the rather extensive ozone literature for further details on both the condensed- and gas-phase reactions. 

It is possible to synthesize two isomeric cycloalkenes of formula C8H14. Both of these compounds react with hydrogen in the presence of platinum to give cyclooctane, and each, on ozonization followed by reduction, gives ... 

Ozonolysis of cycloalkenes.b Cycloalkenes are converted by ozonation in the presence of an alcohol (usually methanol) into an acyclic product with an aldehyde group and an a-alkoxy hydroperoxide group at the terminal positions. The products are usually difficult to purify, but they can be converted into useful products that retain differentiated terminal functionality. 

The rate constants for oxidation of a series of cycloalkenes with ozone have been determined using a relative rate method. The effect of methyl substitution on the oxidation of cycloalkenes and formation of secondary organic aerosols has been analysed.155 Butadiene, styrene, cyclohexene, allyl acetate, methyl methacrylate, and allyl alcohol were epoxidized in a gas-phase reaction with ozone in the absence of a catalyst. With the exception of allyl alcohol, the yield of the corresponding epoxide ranged from 88 to 97%.156 Kinetic control of distereoselection in ozonolytic lactonization has been (g) reported in the reaction of prochiral alkenes.157... 

Ketozonides can also be formed when the keto group and the zwitterion are present in the same molecule and when the distance between them is suitable for ring closure. These conditions are satisfied in the ozonization of 1,2-disubstituted cycloalkenes containing five-mem-bered rings, and even in those containing four-membered rings, Thus 1,2-dimethylcyclopentene forms the ketozonide (113) via the zwitterion (112).24... 

When ozonides are to be isolated, a stream of 2-6% ozone in oxygen is passed through a solution of an alkene or a cycloalkene in low-boiling solvents, such as methyl chloride, pentane, hexane, chloroform, or carbon tetrachloride, at low temperatures (-78 to 5 °C) until the solution acquires a blue tinge (the color of ozone). The solvent is then evaporated at reduced... 

The oldest and still very common cleavage is the reaction of unsaturated compounds with ozone and the subsequent treatment of the ozonides formed (equations 95 and 96). Reduction by strong reducing agents such as complex hydrides gives alcohols [94. Cycloalkenes yield diols [82]. 

A much more frequently used reaction is the cleavage of unsaturated compounds to aldehydes (equations 98 and 99). Alkenes and cycloalkenes that possess one or two hydrogens at the double bonds are oxidized by ozone to ozonides, which have to be reduced to prevent a subsequent oxidation to acids by the excess oxygen atom. Reductions are carried out, usually without isolation of the ozonides, by catalytic hydrogenation over palladium catalyst [80, 81,1106] or Raney nickel [55] or by treatment with... 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

Better yields are often obtained when ozone is used for oxidative cleavage of olefins to carboxylic acids or of cycloalkenes to dicarboxylic acids. Olefinic double bonds are very much more easily attacked by ozone than are aromatic systems, so that arylethylene derivatives can be successfully treated with ozone without appreciable effect on the ring. If the ozonide which is formed initially is decomposed with water, the aldehyde is obtained together with hydrogen peroxide and other products ... 

The yield of OH radicals in the ozonolysis of a number of cycloalkenes has been determined by scavenging OH with cyclohexane (Sidebottom). The derived OH yield of about 40 % was found to be similar to that of cw-2-butene, providing support for the suggestion that OH yields from ozone-alkene reactions depend... 

Kinetics and Mechanism for the Reaction of Ozone with Cycloalkenes... 

The purpose of this research was to obtain kinetic data for the reaction of ozone with cycloalkenes and to determine the formation yields of hydroxyl radicals in these reactions under atmospheric conditions. 

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. 

Second-order rate constants were obtained by monitoring the increased rate of ozone decay in the presence of known excess concentrations of the alkene. In the presence of a cycloalkene, the processes for removing ozone are ... 

Room temperature rate constants and Arrhenius parameters for the gas-phase reactions of ozone with cw-2-butene, 2-methyl-2-butene and a number of cycloalkenes are shown in Table 1 together with the literature values. The rate coefficients for cw-2-butene and 2-methyl-2-butene are in excellent agreement with the data evaluation of Atkinson and Carter [3]. The reported room temperature rate constants for the reaction of ozone with cyclopentene and cyclohexene show a considerable degree of scatter. The present results for cyclopentene provide support for the recent determinations by Bennett et al [24], Nolting et al [25], and Green and Atkinson [21], while the value for cycloheptene is slightly lower than the reported values [20] and [25]. No previous kinetic studies have been carried out on the reactions of O3 with cw-cyclooctene and cw-cyclodecene. 

Rate constants for the reaction of O3 with a number of substituted cycloalkenes were also determined in this work. From the results, the magnitude of the rate constant depends on the nature of the substituent and its position on the ring. As expected, substitution of a hydrogen atom attached at the 1 position in cyclopentene by an electron-withdrawing chlorine atom decreases the reactivity for reaction with the electrophilic ozone molecule. This would appear to be due to both a decrease in the pre-exponential factor and an increase in activation energy. 

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