Mechanism of ozonation reactions

This will ultimately result in decrease of the rate constant. Table 10.2 shows some examples of ozonolysis of saturated polymers—polystyrene and polyisobutylene. These reactions take place not through the mechanism of ozone reaction with the double bonds but through a hidden radical mechanism with rate constants of four to five orders of magnitude lower. 

Razumovskii, S. D. and Zaikov, G. E. Kinetics and mechanism of ozone reaction with double bonds. Uspekhi Khimii. 1980, 49, 2344. 

The kinetics of intermediate and end products formation has been studied and the mechanism of ozone reaction with tetradecane is suggested [66] as ... 

We have studied the kinetics and mechanism of ozone reaction with cycloparaffins ranging from cyclopentane to cyclododecane. From thermodynamically point of view cycloparaffins contain only equivalent C-H-bonds and their energies calculated according to Eqs. (11)-(13), using a model of infinite chain, are 88.9 - 88.5 kcal/mol and for cyclopropane and cyclobutane are 91 and 89.5 kcal/mol. The literature values for the former are within the limits of 94 3 kcal/mol and for the latter are 100.4 2 and 95 3 kcal/mol [28]. The deviations in the calculated and literature values could be attributed to the approximations of the model chosen which considers both the small and big cycles as infinite large. In both cases, however it could be stated that after cyclobutane, D does not actually depend on the cycle size. 

Kefely, A. A. Rakovski, S. K. Shopov, D. M. Razumovskii, S. D. Rakovski, K. S. Zaikov, G. E. Kinetic Relationships and Mechanism of Ozone Reaction with Poly styrene in CC14 Solution. J. Polymer Science Polymer Chem. Edition 1981, 19(6), 2175-2184. 

However, it should be noted that k values of the elastomers are about 2-6 times lower that those of the low molecular analogs. The accuracy of activation energy (E ) determination does not allow to estimate the contribution of the two parameters preexponential factor (A) or for the decrease in k. If we assume that the mechanism of ozone reaction with monomers and elasomers is similar, i.e., the reactions are isokinetic, then A =A At Ik, = 2-5-6 the difference in E at 20°C will be 0.5-1.0 kcal/mole. At the low experimental values of E, these differences will become commensurable and thus the determination of E is not sufficient-... 

This article reviews literature on ozone reaction with diene rubbers. Physical and chemical phenomena of rubber ageing by ozone and mechanisms of ozone reaction with rubbers are described. Possibilities of improving ozone resistance of rubbers and vulcanisates made from... 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

The second term characterizes the chain decomposition of ozone. The mechanism of chain reaction was found to include the following reactions ... 

Despite many decades of research, the mechanisms of ozone-alkene reactions in the gas phase are still not well understood, certainly not as well understood as the corresponding reactions in the condensed phases. Figure 6.4 compares the overall characteristics of these reactions in the gas and condensed phases. 

The reaction mechanism of ozone with the solute should be known to establish a selective oxidation. Non-targeted compounds contained in the water phase should not have a higher reactivity to ozone. Otherwise ozone might already react to a large extent in the aqueous phase, consuming much of the ozone so that it is not available for the oxidation of the target solute in the solvent phase. The achievable selectivity depends much on the distribution of the solute between the gas, water and solvent phase, which should be checked by partition coefficients from the literature or experimentally determined. 

Study of Reaction Mechanisms of Ozone Attack Onto Polymers. 47... 

Figure 3 Direct pathways of ozone reaction with organics. (A) Criegge mechanism. (B) Electrophilic aromatic substitution and 1,3-dipolar cycloaddition. (C) Nucleophilic substitution.

On the other hand, the indirect type of ozonation is due to the reactions of free radical species, especially the hydroxyl radical, with the organic matter present in water. These free radicals come from reaction mechanisms of ozone decomposition in water that can be initiated by the hydroxyl ion or, to be more precise, by the hydroperoxide ion as shown in reactions (4) and (5). Ozone reacts very selectively through direct reactions with compounds with specific functional groups in their molecules. Examples are unsaturated and aromatic hydrocarbons with substituents such as hydroxyl, methyl, amine groups, etc. [45,46],... 

Alkene C=C double bonds also can be cleaved by ozone. The mechanism of this reaction was discussed in connection with Figures 15.47 and 15.48, and it has been explained that... 

The complex 100 is calculated to be more stable than the separated aldehyde and carbonyl oxide by 9 kcal mol-1 and the formation of complex 100 from ethylene and ozone is endothermic by only 3.1 kcal mol-1 <1991CPL(187) 491 >. Cycloaddition then leads to the secondary ozonide 101 (1,2,4-trioxolane). subsequent study of the stereochemistry of ozonation reactions using the AMI method provides further support for the modified Criegee mechanism C1997JOC2757, CHEC-III(6.06.2)193>. 

Knowledge of the major products of the ozonation of Feists ester does not lead immediately to a knowledge of the mechanism of the reaction although the nature of the products makes it obvious that the mechanism is different from that of most ozonations. However, inspection of Table IV, in which product ratios change with changes in conditions and other types of experiments, allows us to rationalize a reasonable mechanistic sequence. The most important points to note are ... 

The role of oxygen derived short-lived radical species in AOPs is still a field of active research. However, extensive knowledge has been accumulated on the mechanism of ozone aqueous chemistry (Rice, 2001, Gottschalk, 2000, Hoigne, 1998). The decomposition of molecular ozone in water by a radical-type chain reaction involves species such as hydrogen trioxide (HO ) with a lifetime of about 10 ps and HO radicals. The latter equilibrate with their dissociation products in about 30 ps, i.e. O3 and OH (Hoigne, 1998) or they decompose into O2 and HO promoting the chain reaction. 

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