Reactions of Ozone

Polycyclic hydrocarbons are extremely reactive with ozone. For example, naphthalene reacted with ozone at a rate about 1500 times faster than benzene (Hoigne and Bader, 1983b), and higher polycyclic hydrocarbons such as phenanthrene, pyrene, and benzo[a]pyrene were also extremely reactive (Butkovic et al., 1983). The experiments of Hoigne and Bader also indicate that the rate constants for reaction of ozone with aromatic hydrocarbons in water were about 100 times greater than in nonpolar solvents such as CCI4. However, aliphatic compounds did not show such a profound solvent effect. 

In organic solvents, ozone undergoes a classic reaction with olefins, reacting rapidly and almost quantitatively with most of these compounds. Carbonyl compounds and carboxylic acids are the products of this reaction. The traditional Crie-gee (cf. Bailey, 1958) mechanism is generally agreed to provide the best rationaliza- 

The initial product of the reaction between ozone and most olefins appears to be the 1,2,3-trioxolane ( ozonide ), which then collapses to a carbonyl compound and a zwitterionic intermediate, 68. In the presence of water, the intermediate hydroxy-hydroperoxide, 69, is produced and decomposes to additional carbonyl-containing compounds. 

Although the majority of aromatic compounds will react with ozone at low pH in water, the relative rates are slower than those of olefins. In general, the order of reactivity is (Bailey, 1958)  

As expected, electron-donating groups enhance the reactivity of the aromatic compound toward ozone, whereas electron-withdrawing groups inhibit it. 

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O ne. Air pollution (qv) levels are commonly estimated by determining ozone through its chemiluminescent reaction with ethylene. A relatively simple photoelectric device is used for rapid routine measurements. The device is caHbrated with ozone from an ozone generator, which in turn is caHbrated by the reaction of ozone with potassium iodide (308). Detection limits are 6—9 ppb with commercially available instmmentation (309). 

In contrast to reaction of ozone with nucleophilic haUde and hypohaUte ions, reaction of ozone with electrophilic hypohalous acids is very slow. 

Unpiotonated hydioxylamine is oxidized rapidly by ozone, / = 2.1 X 10 (39). The reaction of ozone with the lower oxides of nitrogen (NO and NO2) is also rapid and quantitative the end product is nitrogen pentoxide, which is also a catalyst for the decomposition of ozone (45). Nitrous oxide, however, reacts slowly (k < 10 ) (39). Nitrogen-containing anions, eg, nitrite and cyanide, also ate oxidized by ozone (39). Nitrite is oxidized to nitrate (fc = 3.7 X 10 and cyanide is oxidized rapidly to cyanate (fc = 2.6 X 10 (46) and 10 -10 (39)). Cyanate, however, is oxidized slowly. 

The unstable ammonium ozonide [12161 -20-5] NH O, prepared at low temperatures by reaction of ozone withHquid ammonia, decomposes rapidly at room temperature to NH NO, oxygen, and water (51). Tetrametbylammonium ozonide [78657-29-1] also has been prepared. 

Chemiluminescent analyzers are based on the light (chemiluminescence) emitted in the gas-phase reaction of ozone with ethylene, which is measured with a photomultipHer tube. The resulting current is proportional to the ozone concentration (see Luminescent materials, chemiluminescence). 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

The question of the fate of chlorofluorocarbons upon their release into the atmosphere IS of great interest at present because of the potential damage to the earth s protective ozone layer caused by the reaction of ozone with photochemically generated chlorine atoms... 

Isolated reports have appeared of the use of other sources of oxygen for the synthesis of oxaziranes. Belew and Person obtained an oxazirane (8) by the reaction of ozone on isobutylidene-icrf-butyl-... 

A well-known example for a 1,3-dipolar compound is ozone. The reaction of ozone with an olefin is a 1,3-dipolar cycloaddition (see ozonolysis). 

The reaction of ozone with an aromatic compound is considerably slower than the reaction with an alkene. Complete ozonolysis of one mole of benzene with workup under non-oxidative conditions will yield three moles of glyoxal. The selective ozonolysis of particular bonds in appropriate aromatic compounds is used in organic synthesis, for example in the synthesis of a substituted biphenyl 8 from phenanthrene 7 ... 

Compared with uncatalyzed reactions, catalysts introduce alternative pathways that, in nearly all cases, involve two nr more consecutive reaction steps. Each of these steps has a lower activation energy than does the uncatalyzed reaction. We can nse as an example the gas phase reaction of ozone and oxygen atoms. In the homogeneons uncatalyzed case, the reaction is represented to occur in a single irreversible step that has a high activation energy ... 

The principal organic reaction of ozone is its addition to the carbon-carbon double bond of an ethylenic compd. The resulting ozone-olefin addition compd is known as an ozonide. Decompn of the ozonide gives a mixt of oxygenated products containing carbonyl compds and acids. 

The reaction of ozone with an unsaturated organic compd was reported more than a century ago (Schonbein, JPraktChem 66, 282 (1855)), however, complete explanation of this reaction has not been made until recent times. In 1905, Harries (Ref 1) postulated that the addition of ozone to an olefin resulted in the formation of an ozonide according to the formula ... 

The reaction of ozone with olefinic compounds is very rapid. Substiments on the double bond, which donate electrons, increase the rate of reaction, while electron-withdrawing substituents slow the reaction down. Thus, the rate of reaction with ozone decreases as follows polyisoprene > polybutadiene > polychloroprene [48]. The effect of substiments on the double bond is clearly demonstrated in Tables 15.2 and 15.3. Rubbers that contain only pendant double bonds such as EPDM do not cleave since the double bond is not in the polymer backbone. 

Although the cracking of mbbers is related to the reaction of ozone on the double bond, it must be mentioned that ozone reacts also with sulfur cross-links. These reactions, however, are much slower. The reaction of ozone with di- and polysulfides is at least 50 times slower than the corresponding reaction with olefins [49]. 

The protective film mechanism states that the rapid reaction of ozone with the antiozonant produces a film on the surface of the rabber, which prevents attack on the mbber, like waxes do [63]. 

The most effective antiozonants are the substituted PPDs. Their mechanism of protection against ozone is based on the scavenger-protective film mechanism [68-70]. The reaction of ozone with the antiozonant is much faster than the reaction with the C=C bond of the rubber on the rubber surface [56]. The rubber is protected from the ozone attack tUl the surface antiozonant is depleted. As the antiozonant is continuously consumed through its reaction with ozone at the mbber surface, diffusion of the antiozonant from the inner parts to the surface replenishes the surface concentration to provide the continuous protection against ozone. A thin flexible film developed from the antiozonant/ozone reaction products on the mbber surface also offers protection. 

Following this interplay between observations and theory, many atmospheric scientists began studying chemical reactions of ozone in the upper atmosphere. Chemists duplicated atmospheric conditions in the laboratory and measured how fast various chemical reactions occur. The results of these experiments were used to create theoretical models of the upper atmosphere and predict how the ozone concentration would change as CFCs were... 

A reaction of ozone provides an example of concentration effects. Ozone in the atmosphere near the Earth s surface is a serious pollutant that damages soft tissues such as the lungs. In major urban areas, smog alerts are issued whenever there are elevated concentrations of ozone in the lower atmosphere. Nitmgen oxide, another component of photochemical smog, is a colorless gas produced in a side reaction in automobile engines. One reaction that links these species is the reaction of NO and O3 to produce O2 and NO2 ... 

O3 + terpene products Rate =. [03] [terpene] We expect the reaction rate to depend on two concentrations rather than one, but we can isolate one concentration variable by making the initial concentration of one reactant much smaller than the initial concentration of the other. Data collected under these conditions can then be analyzed using Equations and, which relate concentration to time. For example, an experiment could be performed on the reaction of ozone with isoprene with the following initial concentrations ... 

Chlorine atoms catalyze the reaction of ozone with oxygen atoms by forming an unstable CIO intermediate that readily reacts with an O atom, forming another O2 molecule and regenerating the Cl atom. 

We see that chiorine atoms provide an aitemative mechanism for the reaction of ozone with oxygen atoms. The iower-energy pathway breaks down ozone in the stratosphere at a significantiy faster rate than in the absence of the cataiyst. This disturbs the deiicate baiance among ozone, oxygen atoms, and oxygen molecules in a way that poses a serious threat to the iife-protecting ozone iayer. 

Atkinson R, Carter WPL. 1984. Kinetics and mechanisms of the gas-phase reactions of ozone with organic compounds under atmospheric conditions. Chem Rev 84 437-470. 

Clearly, whether or not ozone is formed depends also on the rate at which, for example, unsaturated hydrocarbons react with it. Rates of reactions of ozone with alkanes are, as noted above, much slower than for reaction with OH radicals, and reactions with ozone are of the greatest significance with unsaturated aliphatic compounds. The pathways plausibly follow those involved in chemical ozonization (Hudlicky 1990). 

Gas-phase products from the reactions of ozone with the monoterpenes (-)-p-pinene and (+)-sabinene included the ketones formed by oxidative fission of the exocyclic C=C bonds as well as ozonides from the addition of ozone to this bond (Griesbaum et al. 1998). 

Chan WF, RA Larson (1991) Formation of mutagens from the aqueous reactions of ozone and anilines. Water Res 25 1529-1538. 

Grosjean D, EL Williams, E Grosjean, JM Andino, JH Seinfeld (1993c) Atmospheric oxidation of biogenic hydrocarbons reaction of ozone with 3-pinene, D-limonene, and rra -caryophyllene. Environ Sci Technol 27 2754-2758. 

The analysis of published data on reactions of ozone with low molecular hydrocarbons shows that double bonds react with ozone more quickly than saturated bonds (12). Ozone reacts with saturated hydrocarbons in reactions in which hydrogen abstraction s followed by re-hydridization of the carbon atom form sp to sp state (43,44) ... 

It hag been shown that transition of a backbone carbon from the sp to sp state is promoted by tensile stresses and inhibited by compressive strains (10,44). The acceleration of the process of ozone oxidation of the polymers under load is not associated with the changes in supramolecular structure or segmental mobility of the chain. The probably reason of this effect is a decreasing of the activation energy for hydrogen abstraction (44). The mechanism of initial stages of the reaction of ozone with PP can be represented as ... 

Ozonolysis of organic compounds in water also has biological and environmental93 interest. Ozone preferentially attacks the base moiety of pyrimidine nucleotides in water.94 For example, the reaction of ozone with uracil in water, having no substitutent at 1-position, gave the ozonolysis products in Scheme 3.6.95 The reactions of DNA and RNA with O3 in an aqueous environment are linked to the damage of... 

Bennet, P.J., Harris, S.J., Kerr, J. A. (1987) A reinvestigation of the rate constants for the reactions of ozone with cyclopentene and cyclohexene under atmospheric conditions. Int. J. Chem. Kinet. 19, 609-614. 

Huie, R.E., Herron, J.T. (1975) Temperature dependence of the rate constants for reaction of ozone with some olefins. Int l. J. Chem. Kinet. SI, 165. 

Stedman, D.H., Wu, C.H., Niki, H. (1973) Kinetics of gas-phase reactions of ozone with some olefins../. Phys. Chem. 77, 2511-2514. 

Hoigne, J., Bader, H. (1983) Rate constants of reactions of ozone with organic and inorganic compounds in water. -1. Non-dissociating organic compounds. Water Res. 17, 173-183. 

The most widely used gas-phase chemiluminescence reagent is ozone. Analytically useful chemiluminescence signals are obtained in the reactions of ozone with NO, SO, and olefins such as ethylene and isoprene, but many other compounds also chemiluminesce with ozone. Ozone is conveniently generated online at mixing ratios of =1-5% by electrical discharge of air or 02 at atmospheric pressure [14]. 

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