Nitrate radical aldehyde reactions

Peroxy radicals are also formed in the troposphere through the photolysis of aldehydes (10, 11) and through nitrate radical (N03) reactions (12-14). The hydrogen atom and formyl radical that are formed then react with molecular oxygen (02) (reactions 11 and 12) under tropospheric conditions. 

Atkinson R, Aschmann SM, Goodman MA. 1987. Kinetics of the gas-phase reactions of nitrate radicals with a series of alkynes, haloalkenes, and alpha, beta-unsaturated aldehydes. Int J Chem Kinet 19 299-308. 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

Aldehydes are emitted by combustion processes and also are formed in the atmosphere from the photochemical degradation of other organic compounds. Aldehydes undergo photolysis, reaction with OH radicals, and reaction with N03 radicals in the troposphere. Reaction with N03 radicals is of relatively minor importance as a loss process for these compounds, but can be a minor contributor to the H02 (from formaldehyde) and peroxyacetyl nitrate (PAN) formation during nighttime hours (Stockwell and Calvert, 1983 Cantrell et al., 1985). Thus, the major loss processes involve photolysis and reaction with OH radicals. 

Nitrate radicals (NO3) are formed by the reaction of O3 and NO2 (Sect. 5.4.2) and play an important role in atmospheric chemistry at nighttime in polluted air. NO3 has an absorption spectrum in the visible region as seen in Sect. (4.2.4) so that daytime concentration is very low since it is easily photodecomposed by sun light. Simultaneously, since the reaction rate constant of NO3 with NO is large, it returns easily to NO2 by NO so that its concentration near NO sources is also very low. NO3 reacts with alkenes and aldehydes to form dinitrates and OH/HO2 radicals at nighttime. Rate constants of fundamental reactions of atmospheric NO3 and related N2O5 are cited in Table 5.6. 

Reaction of butanal with all three reactive species leads primarily to the formation of the butanoyl radical by abstraction of the aldehydic H-atom. Papagni et al. (2000) noted an increase in the rate coefficient of OH with butanal, compared with that with propanal, which is compatible with the sensitization of the C—H bond to the carbonyl group proposed by Kwok and Atkinson (1995). Application of their structure-activity relations (SARs) gives 17% abstraction at this site with a channel yield of 78% for production of the acyl radical. Reaction of the acylperoxy radical with NO2 forms peroxybutanoyl nitrate, while reaction with NO forms CO2 and the -propyl radical, which then reacts with O2 to form the n-propylperoxy radical, whose main atmospheric fate is conversion to propanal. 

D Anna, B., and C.J. Nielsen (1997), Kinetic study of the vapour-phase reaction between aliphatic aldehydes and the nitrate radical, J. Chem. Soc., Faraday Trans., 93, 3479-3483. 

Noda, J., C. Holm, G Nyman, S. Langer, and E. Ljungstrom (2003), Kinetics of the gas-phase reaction of n-Cg-Cio aldehydes with the nitrate radical, Int. J. Chem. Kinetics, 35, 120-129. 

Mino and Kaizerman [12] established that certain. ceric salts such as the nitrate and sulphate form very effective redox systems in the presence of organic reducing agents such as alcohols, thiols, glycols, aldehyde, and amines. Duke and coworkers [14,15] suggested the formation of an intermediate complex between the substrate and ceric ion, which subsequently is disproportionate to a free radical species. Evidence of complex formation between Ce(IV) and cellulose has been studied by several investigators [16-19]. Using alcohol the reaction can be written as follows ... 

Complex reactions involving radicals occur, giving rise to secondary pollutants such as ozone, aldehydes, peroxyacetyl nitrate (PAN) and particulate matter. 

Ellis and coworkers studied the effect of lead oxide on the thermal decomposition of ethyl nitrate vapor.P l They proposed that the surface provided by the presence of a small amount of PbO particles could retard the burning rate due to the quenching of radicals. However, the presence of a copper surface accelerates the thermal decomposition of ethyl nitrate, and the rate of the decomposition process is controlled by a reaction step involving the NO2 molecule. Hoare and coworkers studied the inhibitory effect of lead oxide on hydrocarbon oxidation in a vessel coated with a thin fQm of PbO.P l They suggested that the process of aldehyde oxidation by the PbO played an important role. A similar result was found in that lead oxide acts as a powerful inhibitor in suppressing cool flames and low-temperature ignitions.P l... 

When an explosive slowly decomposes, the products may not follow the previously described hierarchy or be at the maximum oxidation states. The nitro, nitrate, nitramines, acids, etc., in an explosive molecule can break down slowly. This is due to low-temperature kinetics as well as the influence of light, infrared, and ultraviolet radiation, and any other mechanism that feeds energy into the molecule. Upon decomposition, products such as NO, NO2, H2O, N2, acids, aldehydes, ketones, etc., are formed. Large radicals of the parent explosive molecule are left, and these react with their neighbors. As long as the explosive is at a temperature above absolute zero, decomposition occurs. At lower temperatures the rate of decomposition is infinitesimally small. As the temperature increases, the decomposition rate increases. Although we do not always, and in fact seldom do, know the exact chemical mechanism, we do know that most explosives, in the use range of temperatures, decompose with a zero-order reaction rate. This means that the rate of decomposition is usually independent of... 

Compounds whose radical anions give follow-up reactions can be reduced, and the reaction medium (aqueous or non-aqueous) eventually governs the nature of the final products. A number of organic substrates such as aldehydes, ketones and alkynes have been reduced in this way. It is also possible to reduce substrates which have a potential much more negative than its standard redox potential. For instance, nitrate, nitrite and carbon dioxide are reduced [2]. In the latter case [157], the overpotential reaches 0.6 V and the reaction is still rapid because the rate of the follow-up reaction, i.e. the dimerization of C02 , is extremely high (it= 10 M- s- ) [158]. 

However, near the Earth s surface, the hydrocarbons, especially olefins and substituted aromatics, are attacked by the free atomic O, and with NO, produce more NO2. Thus, the balance of the reactions shown in the above reactions is upset so that O3 levels build up, particularly when the Sun s intensity is greatest at midday. The reactions with hydrocarbons are very complex and involve the formation of unstable intermediate free radicals that undergo a series of changes. Aldehydes are major products in these reactions. Formaldehyde and acrolein account for 50% and 5%, respectively, of the total aldehyde in urban atmospheres. Peroxyacetyl nitrate (CH3COONO2), often referred to as PAN, and its homologs, also arise in urban air, most likely from the reaction of the peroxyacyl radicals with NO2. 

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