Atmospheric ozonolysis

Atmospheric ozonolysis is believed to be a major pathway for the degradation of the vast quantities of biogenic and anthropogenic alkenes emitted annually. Analysis of air and precipitation has indicated that H2O2, alkyl hydroperoxides and 1-hydroxyalkyl hydroperoxides (1-HAHPs) are present [1]. Since both ozonolysis and other oxidation processes can lead to hydroperoxides, it is of interest to know to what extent ozonolysis is involved in the formation of those hydroperoxides actually found in the atmosphere. 

Ozonolysis in the gas phase leads to peroxide products and is especially interesting in that regard, because some of these peroxides can be formed even in the presence of NOx. The studies described here provide information about the yields and identity of hydroperoxide products in gas-phase ozonolysis under two sets of conditions highly relevant to the troposphere. These products must be part of any mechanism that purports to explain atmospheric ozonolysis. Since peroxides are a source of radicals and a reservoir of oxidising power, their concentrations must be considered in quantitative descriptions of the tropospheric ozone budget. 

Quantum chemical calculations based on the CCSD(T)/6-31G(d)-l-CF//B3LYP/ 6-3H-G(d,p) level of theory have been used to investigate the mechanisms of atmospheric ozonolysis of methyl acrylate to methyl glyoxylate and formaldehyde, and... 

Low-temperature spectroscopy is indispensable for the studies of processes on the ice surface, illustrated by ozone adsorption and ethylene ozonolysis. Such results are important to clarify the mechanism of atmospheric pollutant elimination and air purification in the nature. 

Ozonolysis in the gas phase is not generally carried out in the laboratory. However, the reaction is important because it takes place in the atmosphere and contributes to air pollution. There is much evidence that the Criegee mechanism operates in the gas phase too, though the products are more complex beeause of other reactions that also take plaee. ... 

Most of the concern for the toxicity of the atmospheres associated with fires has focused on vapors and gases. Vapors and gases are the components that are known to cause acute toxicity, and at high concentrations can lead to incapacitation and death. It is clear, however, that the smokes from fires also have particulate components in the form of soot and chemical reaction products, such as metallic oxides or ozonolysis products. The toxicity of these materials must also be considered. 

Grimsrud, E. P., H. H. Westberg, and R. A. Rasmussen. Atmospheric reactivity of monoterpene hydrocarbons, NOs photooxidation and ozonolysis. Int. J. Chem. Kinet. Symp. 1 (Chemical Kinetics Data for the Lower and Upper Atmosphere) 183-195, 1975. 

Stedman, D. H., and H. Niki. Ozonolysis rates of some atmospheric gases. Environ. Lett. 4 303-310, 1973. 

Trioxolane (1) has only been prepared by the ozonolysis of ethylene. The rearrangement of the primary ozonide occurs above — 100°C to give 1,2,4-trioxolane as a colorless, explosive liquid <42LA(553)187>. 1,2,4-Trithiolane (2) is still best prepared by a classical reaction of Na2S2.5 with excess dichloromethane. Some 1,2,4,5-tetrathiolane is also produced, but (2) can be isolated as a pale-yellow distillable liquid. It is best kept stored under inert atmosphere below 0°C to avoid polymerization <67CPB988>. Parent compounds (3)-(6) are not known and the 1- and 4-5-oxides for 1,2,4-trithiolane have been mentioned previously (see Section 4.16.5.2.3). 

Ozonolysis of pyrethroids generates ozonide products and epoxides which show mild levels of bacterial mutagenicity <86Mi 4i6-03>. This has possible implications for atmospheric oxidation of pesticides or ozonolytic treatment of waste water. 

Gutbrod, R., E. Kraka, R. N. Schindler, and D. Cremer, Kinetic and Theoretical Investigation of the Gas-Phase Ozonolysis of Isoprene Carbonyl Oxides as an Important Source for OH Radicals in the Atmosphere, J. Am. Chem. Soc., 119, 7330-7342 (1997a). 

Overall, while the combinations of substrate effects, ambient NOz levels, and other gas-particle phenomena preclude a definitive answer, the formation of significant amounts of nitroarenes in heterogeneous particle-phase N02-PAH, atmospheric reactions seems unlikely, e.g., much slower than photooxidation or ozonolysis. This conclusion also applies to heterogeneous reactions of N205 with particle-bound PAHs on diesel and wood soot (Kamens and co-workers, 1990 see also Pitts et al., 1985c, 1985d, 1985e). 

The incremental reactivity of a VOC is the product of two fundamental factors, its kinetic reactivity and its mechanistic reactivity. The former reflects its rate of reaction, particularly with the OH radical, which, as we have seen, with some important exceptions (ozonolysis and photolysis of certain VOCs) initiates most atmospheric oxidations. Table 16.8, for example, also shows the rate constants for reaction of CO and the individual VOC with OH at 298 K. For many compounds, e.g., propene vs ethane, the faster the initial attack of OH on the VOC, the greater the IR. However, the second factor, reflecting the oxidation mechanism, can be determining in some cases as, for example, discussed earlier for benzaldehyde. For a detailed discussion of the factors affecting kinetic and mechanistic reactivities, based on environmental chamber measurements combined with modeling, see Carter et al. (1995) and Carter (1995). 

The reduction of acrylic acid was attempted at elevated temperatures. Surprisingly, the reaction was found to yield not only propionic acid, but also the dimer, a-methylglutaric acid. When the reaction was conducted in the absence of hydrogen, the product obtained was 3-methylglutaconic acid, which apparently is the precursor of the saturated dimer formed in a hydrogen atmosphere. Similarly, methacrylic acid yielded a-methylene-y,y-dimethylglutaric acid when heated with cyanocobaltate (II) in the absence of hydrogen. Its structure was established via ozonolysis. Similar dimerizations have been reported for acrylic acid (I, 14), methacrylate ester (7, 11), crotonic acid (13), and its diethylamide (15). 

Norgaard, A.W., Nojgaard, J.K., Larsen, K., Sporring, S., Wilkins, C.K., Clausen, P.A. and Wolkoff, P. (2006) Secondary limonene endo-ozonide a major product from gas-phase ozonolysis of R-(+)-limonene at ambient temperature. Atmospheric Environment, 40, 3460-6. 

Fick, J., Pommer, L., Asttand, A., Ostin, R., Nilsson, C. and Andersson, B. (2005) Ozonolysis of monoterpenes in mechanical ventilation systems. Atmospheric Environment, 39, 6315-25. 

Warscheid, B. and Hoffmann, T. (2001) On-line measurements of alpha-pinene ozonolysis products using an atmospheric pressure chemical ionization ion-trap mass spectrometer. Atmospheric Environment, 35, 2927-40. 

A comparison of various calculations revealed <1997PCA9421> that an accurate description of the ozonolysis of ethene is obtained at the CCSD(T) level with a TZ+2P basis set, while other methods, which cover less correlation effects, fail to provide a consistent description of all reaction steps. It was shown that the primary ozonides (1,2,3-trioxolanes) are not collisionally stabilized under atmosphere conditions <1997PCA9421>. 

Ozonolysis of cis-3,4-Dimethyl-3 -hexene. A solution of cis-3,4-di-methyl-3-hexene (98% pure, Chemical Samples Co.) (1.12 grams, 10 mmoles) in 50 ml pentane was ozonized at — 62°C until the blue color of excess ozone was evident. A nitrogen stream was used to purge the solution of excess ozone. Pentane was then carefully distilled off at atmospheric pressure. A water aspirator (20 mm Hg) was then used to remove the ketone product. Treatment of this material with 10 ml of an 0.1 M solution of 2,4-dinitrophenylhydrazine gave 2.33 grams of crude 2,4-dinitrophenylhydrazone. The crude product was recrystallized and identified as the 2,4-dinitrophenylhydrazone of methyl ethyl ketone, mp 115-116°C. Yield of the ketone was 92% based on olefin used. 

Another potential dark source of in the atmosphere, more particularly in the boundary layer, is from the reactions between ozone and alkenes. The ozonolysis of alkenes can lead to the direct production of the OH radical at varying yields (between 7 and 100%) depending on the structure of the alkene, normally accompanied by the co-production of an (organic) peroxy radical. As compared to both the reactions of OH and NO3 with alkenes the initial rate of the reaction of ozone with an alkene is relatively slow, this can be olfset under regimes where there are high concentrations of alkenes and/or ozone. For example, under typical rural conditions the atmospheric lifetimes for the reaction of ethene with OH, O3 and NO3 are 20 h, 9.7 days and 5.2 months, respectively in contrast, for the same reactants with 2-methyl-2-butene the atmospheric lifetimes are 2.0 h, 0.9 h and 0.09 h. 

A classical study on the fate of tetraalkyl compounds in the atmosphere shows the effect of photochemical oxidation on the breakdown of R4Pb. Direct ozonolysis of Mc4Pb (equation 53) presumably proceeds by analogy to the process in tetraethyltin . 

During the course of studies on butatriene, 1,5-cyclooctadiyne (83) was isolated as colourless crystals . It decomposed at 105 °C and was found to be stable at 0 °C under an inert atmosphere. Cyclooctane was obtained quantitatively on catalytic hydrogenation of 83. Ozonolysis of 83 gave succinic acid as a sole product. 

---