Rate constants of ozonation

The very low yield of radicals by the reaction of ozone with cumene was found to be the result of the intensive ozone reaction with the benzene ring of cumene with molozonide formation. The values of the parameter e in other reactions are typical of the cage effect of radical pairs in solutions. The rate constants of ozone reactions with various compounds are presented in Table 3.7 and Table 3.8. 

Rate Constants of Ozone Reaction with Organic Compounds (Experimental Data)... 

Photolysis of atmospheric pollutants by solar radiation results in an increase of ozone concentration in certain urban areas and is the cause of a sequence of oxidation reactions with polymers. Ozone reacts with practically all organic materials especially with alkenes. The rate of its reaction with alkene is several orders of magnitude higher than that with alkane. The ratio of the rate constants of ozone with ethene/ethane is 1.5 x 105, with propene/propane 1.6 x 106, and with butene- 1/butane 1.1 x 106, at room temperature [5],... 

As stated earlier, the rate constants of ozone with organic compounds differ greatly for both types of processes (Table 3). The first reaction is important in acid media and for solutes that react very fast with ozone such as, for example, unsaturated compounds and compounds containing amine or acid groups. The results support the electrophilic nature of the reaction, either by electrophilic substitution or by dipolar cycloaddition [37]. This route leads to a very limited mineralization of the organic compounds, and its use for the removal of pollutants must be reinforced by modification of the method. 

A second method of measuring the rate constants of ozonation was attempted. This alternate method involved the pre-saturation of a known volume of CHC13 at 0°C with ozone. An equimolar amount of organo-mercurial in CHC13 was then added to the 03 solution, and both reagents were allowed to decrease in concentration. This attempted second-order rate analysis failed, however, since the necessarily low concentration of ozone (0.0163M) did not yield reliable NMR mercurial integrations. Hence the data were quite scattered and inconsistent. 

The ozonation of dyes at various initial pH levels (4, 7 and 10) were also examined, and is shown in Figure 18. The pseudo first-order rate constants of ozonation of all selected dyes varied from 5.2 x 10 4 to 1.2 x 10 s 1 at pH 4, 1.5 x KT to 5.1 x KT4 s 1 at pH 7, and l.l x l O 4 to 6.3 x I0"4 s 1 at pH 10, respectively, as shown in Figure 18. The decay rates of azo dyes were found to increase with the increment of the pH, and the solution pH decreased during ozonation. In general, ozone oxidation pathways include direct oxidation by ozone or radical oxidation by OH radical. Direct oxidation is more selective and predominates under acidic conditions, while radical oxidation is less selective and predominates under basic conditions. Since the oxidation potential of hydroxyl radicals is much higher than that of the ozone molecule, direct oxidation is slower than radical oxidation. 

TABLE 10.2 Rate constants of ozone reactions with polymers and low molecular analogs... 

It is evident that the rate constants of ozone interaction with ketone, measured by the static method (Fig. 6) through mixing of ozone and ketone solutions at [K] [03] are higher than those found by the bubbling method (Table 6). This is not difficult to explain because in the former case the obtained values represent the total effective constant of interaction of both the enol and the keto form. 

In order to assess the validity of the kinetic schemes we have experimentally determined the rate constants of ozone interaction with 24 paraffins of various structures. The rate constants depending on [RH] are given... 

FIGURE 3 Dependence of the rate constant of ozone reaction with cyclooctane at 10°C. 

The catalytic properties of the metal ions under other equal conditions depend on their rate constant with ozone [102]. For that reason we have determined the values of k in the presence of different transition metals in cumene-AcOH medium. In Table 10 are presented the rate constants of ozone reaction with some transition metals ions at 20°C in cumene AcOH solution (1 1, v v). 

Experimentally determined reaction rate constant of ozone interaction with -C=C- bonds in the polymer of Indian rubber latex are of the order of 2-6x10 L/mole-s. Therefore, reaction rate of the unsaturated polymer of isoprene is mainly limited by supply rate of ozone into reactor. 

The results of determination of the rate constant of ozone decomposition kp at different temperatures are suimnarized in Table 1.1, where were found the parameters of Arrhenius equation ... 

The rate constant of ozone reaction with NO is about 1010 cm /(mol s), and with NO2 it is 107 cmV(mol.s) whereby the oxidation of NO by ozone in the liquid phase is characterized by a higher absorption rate and rise in the concentration of the obtained HNO3. Moreover, the oxidation of NO can be accomplished in the exhaust gases or in the course of absorption [12],... 

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