Atmosphere alkene reactions

Adeniji, S.A., Kerr, J.A., Williams, M.R. (1981) Rate constants for ozone-alkene reactions under atmospheric conditions. Int. J. Chem. Kinet. 13, 209-217. 

Grosjean, D., Grosjean, E., Williams, II, E.L. (1994) Atmospheric chemistry of olefins A product study of the ozone — alkene reaction with cyclohexane added to scavenge OH. Environ. Sci. Technol. 26, 186-196. 

In atmospheric chemistry, reactions between pure nitric oxide and a range of activated alkenes have been examined. However, no addition products were observed." Only in the presence of NO2 was addition to give jS-nitroalkyl radicals, followed by trapping to /3-nitronitroso compounds, observed. These final products can also trap other radicals to give aminoxyl radicals. 

As for other organics in the atmosphere, the OH radical is a major oxidant for alkenes. Table 6.8 gives the rate constants for some OH-alkene reactions as well as their temperature dependence in Arrhenius form. Several points are noteworthy (1) the reactions are very fast, approaching 10-l() cm3 molecule-1 s-1 for the larger alkenes (2) the rate constants have a pressure dependence (3) the apparent Arrhenius activation energies are negative. ... 

Grosjean, D E. Grosjean, and E. L. Williams, Atmospheric Chemistry of Olefins A Product Study of the Ozone-Alkene Reaction with Cyclohexane Added to Scavenge OH, Emiron. Sci. TechnoL, 28, 186-196 (1994c). 

Onsager inverted snowball theory (Com.) relation to Smoluchowski equation in, 35 relaxation time by, 34 rotational diffusion and, 36 Ozone in the atmosphere, 108 alkene reactions with, 108 Crigee intermediate from, 108 molozonide from, 108 ethylene reaction with, 109 acetaldehyde effect on, 113 formic anhydride from, 110 sulfur dioxide effect on, 113 sulfuric acid aerosols from, 114 infrared detection of, 108 tetramethylethylene (TME) reaction with, 117... 

Experimental studies have shown that ozone-alkene reactions in the gas phase likewise proceed via intermediate formation of 1,2,3-trioxolanes (primary ozonides) whose spontaneous decomposition then as a rule leads to a variety of subsequent products, including 1,2,4-trioxolanes (81JA3807). Because ozone is present in the atmosphere (from 0.02p.p.m. at sea level up to 0.2 p.p.m. and more in industrial and urbanized areas), reactions of... 

In contrast to the water phase the HO radicals can have a much longer lifetime in gaseous media, i.e. up to 1 s for the OH and 60 s for the HO radical, respectively (Fabian, 1989). Despite the low concentration of OH radicals of about 10 molecules per cm in the sunlit troposphere (Ehhalt, 1999) they play an important role in controlling the removal of many organic natural and manmade compounds from the atmosphere (Eisele et al., 1997, Eisele and Bradshaw, 1993). Even in indoor environments, the formation of hydroxyl radicals is possible by ozone/alkene reactions (Atkinson et al., 1995). Steady-state indoor hydroxyl radical concentrations of about 6.7x10 ppb equivalent to 1.7x10 molecules cm were calculated at an ozone concentration of 20 ppb (Weschler and Shields, 1996). 

When water-free salts of linear or branched perfluorinated acids, containing three or more carbon atoms, are heated over their melting points in a dry atmosphere, a reaction takes place to give an alkene, carbon dioxide and a fluoride salt. 

A 35-mL sealed tube was charged with a solution of [dichloro(phenyl)methyl](phenyl)mercury (6.56 g, 15.0 mmol) and (Z)-but-2-ene (ca. 6 g, 110 mmol, passed through a drying tower containing CaClj and MgS04) in benzene (10 mL). The tube was sealed and shaken for 15 h at 75°C. At the end of this time, the reaction vessel was cooled and opened and the alkene was allowed to evaporate under a Nj atmosphere. The reaction mixture was washed with hexane through a filter which separated 4.35 g (92 /o) of chloro(phenyl)mercury and then concentrated at reduced pressure. Short-path distillation of the concentrate using an oil bath heat source (max temperature 85"C) afforded the product yield 0.77 g (28%) bp 51 -56°C/0.2 Torr ratio (cisitrans) 2.4. 

Moller, D. (1988) Production of free radicals by an ozone-alkene reaction - a possible factor in the new-type forest decline Atmospheric Environment 22, 2607-2611 Moller, D. (1989) The possible role of H2O9 in new-type forest decline. Atmospheric Environment 23, 1187-1193... 

The results of LACTOZ have provided an extended kinetic data base for the following classes of reactions reactions of OH with VOCs, reactions of NO3 with VOCs and peroxy radicals, reactions of O3 with alkenes, reactions of peroxy radicals (self reactions, reaction with HO2, other RO2, NO, NO2), reactions of alkoxy radicals (reactions with O2, decomposition, isomerisation), thermal decomposition of peroxynitrates. Photolysis parameters (absorption cross-section, quantum yields) have been refined or obtained for the first time for species which photolyse in the troposphere. Significantly new mechanistic information has also been obtained for the oxidation of aromatic compounds and biogenic compounds (especially isoprene). These different data allow the rates of the processes involved to be modelled, especially the ozone production from the oxidation of hydrocarbons. The data from LACTOZ are summarised in the tables given in this report and have been used in evaluations of chemical data for atmospheric chemistry conducted by international evaluation groups of NASA and lUPAC. 

Although ozone-alkene reactions were not specified in the original objectives of LACTOZ they constitute a loss process for ozone and are important for degradation of unsaturated hydrocarbons, in particular alkenes with multiple double bonds and complex structures, such as are found in the biogenic hydrocarbons. Emphasis in LACTOZ has been on the rates and mechanisms under atmospheric conditions. These studies led to downward revision of the rate constants of the O3 alkene reactions, due to complications arising in many earlier investigations from secondary reactions of radicals produced in the primary step. Some important hitherto unknown aspects of ozone reactions, such as the formation of peroxides and their dependence on the water vapour concentrations, have been discovered in LACTOZ. 

All carbonyl oxides proved to be highly photolabile, and on photolysis yield dioxiranes 3 or split off oxygen atoms to produce ketones. Oxygen atoms are also formed thermally from vibrationally excited 1. Thus, if the large exothermicity of the ozonolysis reaction is taken into account, 1 might be a source of O atoms and OH radicals in the troposphere. The role of dioxiranes has not yet been discussed in context with atmospheric chemistry, although the formation of these species in contrast to the isomeric carbonyl oxides - in ozone/alkene reactions has been unequivocally demonstrated [13]. 

Table 7.3 The yields of OH in the Os-alkene reactions under the atmospheric pressure...

As seen in Reaction Scheme 7.3, in the NO3 and alkene reactions epoxy alkanes (also called epoxides or oxiranes), hydroperoxy nitrates, carbonyl nitrates and dinitrates are produced characteristically (Bandow et al. 1980 Kwok et al. 1996a Calvert et al. 2000), and some of them have been detected in the polluted atmosphere (Schneider et al. 1998). Recently, reactions of NO3 with alkenes are interesting from the view point of organic aerosol formation (Gong et al. 2005 Ng et al. 2008). 

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

Similarly to alkenes. alkynes also insert. In the reaction of 775 carried out under a CO atmosphere in AcOH, sequential insertions of alkyne, CO. alkene. and CO take place in this order, yielding the keto ester 776[483]. However, the same reaction carried out in THF in the presence of LiCl affords the ketone 777, but not the keto ester[484]. The tricyclic terpenoid hirsutene (779) has been synthesized via the Pd-catalyzed metallo-ene carbonylation reaction of 778 with 85% diastereoselectivity as the key reaction[485], Kainic acid and allo-kainic acid (783) have been synthesized by the intramolecular insertion ol an alkene in 780, followed by carbonylation to give 781 and 782[486],... 

Kharasch called this the peroxide effect and demonstrated that it could occur even if peroxides were not deliberately added to the reaction mixture Unless alkenes are pro tected from atmospheric oxygen they become contaminated with small amounts of alkyl hydroperoxides compounds of the type ROOH These alkyl hydroperoxides act m the same way as deliberately added peroxides promoting addition m the direction opposite to that predicted by Markovmkov s rule... 

The important hydrocarbon classes are alkanes, alkenes, aromatics, and oxygenates. The first three classes are generally released to the atmosphere, whereas the fourth class, the oxygenates, is generally formed in the atmosphere. Propene will be used to illustrate the types of reactions that take place with alkenes. Propene reactions are initiated by a chemical reaction of OH or O3 with the carbon-carbon double bond. The chemical steps that follow result in the formation of free radicals of several different types which can undergo reaction with O2, NO, SO2, and NO2 to promote the formation of photochemical smog products. 

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

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