Radicals nitrate

Other techniques for decompng nitric acid are photochemical flash photolysis. The photochemical decompn of nitric acid is not solely a gas-phase reaction X-rays have caused the evolution of 02 from nitric acid crystals. The use of flash photolysis has shown the nitrate radical to be an intermediate in the decompn (Ref 30)... 

In addition to reactions with HO, tropospheric organic compounds may be oxidized by ozone (via ozonation of non-aromatic carbon/carbon double bonds, Atkinson 1990) and in some cases by reaction with nitrate radical, described below. Table I gives representative trace-gas removal rates for these three processes. In spite of these competing reactions, HO largely serves as... 

Table I. Trace gas rate constants and lifetimes for reaction with ozone, hydroxyl radical, and nitrate radical. Lifetimes are based upon [O3]=40ppb [HO ]=1.0x10 molecules cm (daytime) [NO3 ]=10ppt (nighttime).

Reactions in the troposphere are mediated by reactions involving hydroxyl radicals produced photochemically during daylight, by nitrate radicals that are significant during the night (Platt et al. 1984), by ozone and, in some circumstances by 0( P). 

Nitrate radicals are formed from NO that is produced during combustion processes and these are significant only during the night in the absence of photochemically produced OH radicals. They are formed by the reactions... 

The concentrations of all these depend on local conditions, the time of day, and both altitude and latitude. Values of ca. 10 molecules/cm for OH, 10 -10 ° molecules/cm for NO3, and ca. 10 molecules/cm for ozone have been reported. Not all of these reactants are equally important, and the rates of reaction with a substrate vary considerably. Reactions with hydroxyl radicals are generally the most important, and some illustrative values are given for the rates of reaction (cmVs/molecule) with hydroxyl radicals, nitrate radicals, and ozone (Atkinson 1990 summary of PAHs by Arey 1998)... 

The major reactions carried out by hydroxyl and nitrate radicals may conveniently be represented for a primary alkane RH or a secondary alkane RjCH. In both, hydrogen abstraction is the initiating reaction. 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

The kinetics of the reactions of several xenobiotics with hydroxyl or nitrate radicals have been examined under simulated atmospheric conditions and include those given in Table 1.1. 

Considerable attention has been directed to the formation of nitroarenes that may be formed by several mechanisms (a) initial reaction with hydroxyl radicals followed by reactions with nitrate radicals or NO2 and (b) direct reaction with nitrate radicals. The first is important for arenes in the troposphere, whereas the second is a thermal reaction that occurs during combustion of arenes. The kinetics of formation of nitroarenes by gas-phase reaction with N2O5 has been examined for naphthalene (Pitts et al. 1985a) and methylnaphthalenes (Zielinska et al. 1989) biphenyl (Atkinson et al. 1987b,c) acephenanthrylene (Zielinska et al. 1988) and for adsorbed pyrene (Pitts et al. 1985b). Both... 

Chlodini G, B Rindone, F Cariati, S Polesello, G Restelli, J Hjorth (1993) Comparison between the gas-phase and the solution reaction of the nitrate radical and methylarenes. Environ Sci Technol 27 1659-1664. 

Platt UF, AM Winer, HW Biermann, R Atkinson, JN Pitts, Jr (1984) Measurement of nitrate radical concentrations in continental air. Environ Sci Technol 18 365-369. 

Reactions that simnlate tropospheric conditions have been carried ont in Teflon bags with volumes of ca. 6 m htted with sampling ports for introduction of reactants and snbstrates, and removal of samples for analysis. Substrates can be added in the gas phase or as aerosols that form a surface him. The primary reactants are the hydroxyl and nitrate radicals, and ozone. These mnst be prepared before use by reactions (a) to (c). 

Extensive research has been conducted into the atmospheric chemistry of organic chemicals because of air quality concerns. Recently, Atkinson and coworkers (1984, 1985, 1987, 1988, 1989, 1990, 1991), Altshuller (1980, 1991) and Sabljic and Glisten (1990) have reviewed the photochemistry of many organic chemicals of environmental interest for their gas phase reactions with hydroxyl radicals (OH), ozone (03) and nitrate radicals (N03) and have provided detailed information on reaction rate constants and experimental conditions, which allowed the estimation of atmospheric lifetimes. Klopffer (1991) has estimated the atmospheric lifetimes for the reaction with OH radicals to range from 1 hour to 130 years, based on these reaction rate constants and an assumed constant concentration of OH... 

Winer, A.M., Atkinson, R., Pitts, J.N., Jr. (1984) Gaseous nitrate radical possible nighttime atmospheric sink for biogenic organic compounds. Science 224, 156-159. 

Carter, W.P.L., Winer, A.M., Pitts, Jr., J.N. (1981) Major atmospheric sink for phenol and the cresols. Reaction with the nitrate radical. Environ. Sci. Technol. 15, 829-831. 

The detailed model was constructed as described by Carslaw et al. (1999, 2002). Briefly, measurements of NMHCs, CO and CH4 were used to define a reactivity index with OH, in order to determine which NMHCs, along with CO and CH4, to include in the overall mechanism. The product of the concentration of each hydrocarbon (and CO) measured on each day during the campaign and its rate coefficient for the reaction with OH was calculated. All NMHCs that are responsible for at least 0.1% of the OH loss due to total hydrocarbons and CO on any day during the campaign are included in the mechanism (Table 2). Reactions of OH with the secondary species formed in the hydrocarbon oxidation processes, as well as oxidation by the nitrate radical (NO3) and ozone are also included in the... 

Reductive scission of the nitrate radical and methylation with the Purdie... 

Proof of Constitution.—Reference to Table XII will show that all of the methods mentioned above as being suitable for the synthesis of 4,6-dimethylglucose have been correlated by means of crystalline derivatives. If the tosyl, benzyl and nitrate radicals can be regarded as being non-migratory (and there is no evidence to the contrary) then the course of the synthesis from 4,6-acetals (the constitution of which has been proved by their conversion into 2,3-dimethyl-D-glucose) leaves no doubt that the methyl groups occupy positions 4 and 6. 

The agreement between rate coefficients for reaction of N03 derived from the decomposition of N2Os and NOz has led to the suggestion that the same N03 intermediate is involved in both reactions. This is believed to be the symmetrical (D3h) nitrate radical because of the agreement between calculated and experimentally determined values of (/) the entropy of a D3h nitrate radical226 and (ii) the equilibrium constant fc30/fc 30215 226. 

N-nitrosomethlyphenylamine N-nitrosomethlyphenylamine TV-nitroso compounds nitric oxide nitrogen dioxide nitrate radical nitrite radical nitrogen trioxide... 

Reaction with the nitrate radical. Environ Sci Technol 15 829-831. 

Finally, the oxidation of nitrate anions leads to nitrate radicals (NOs ) that add to olefins (Scheme 14) [37]. These oxidations were carried out at a platinum anode using constant current conditions, an undivided cell, a mixed MeCN H2O Et20 solvent system, and LiN03 as the electrolyte. The initial oxidation led to a nitrate product that was not stable and hence... 

The amount of cyanogen chloride formed was inversely proportional to the pH of the solution. At pH 6, the greatest amount of cyanogen chloride was formed when the reaction mixture contained ammonium ion and hypochlorous acid at a ratio of 2 3 (Kanno et al., 1982). Benzene vapor reacted with nitrate radicals in purified air forming nitrobenzene (Chiodini et al., 1993). 

Chemical/Physical. Products identified from the reaction of toluene with nitric oxide and OH radicals include benzaldehyde, benzyl alcohol, 3-nitrotoluene, p-methylbenzoquinone, and o, m, and p-cresol (Kenley et ah, 1978). Gaseous toluene reacted with nitrate radicals in purified air forming the following products benzaldehyde, benzyl alcohol, benzyl nitrate, and 2-, 3-, and 4-nitro-toluene (Chiodini et al., 1993). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of benzaldehyde, benzyl nitrate, 3-nitrotoluene, and o-, m-, and p-cresol (Finlayson-Pitts and Pitts, 1986 Atkinson, 1990). 

In the gas phase, p-xylene reacted with nitrate radicals in purified air forming 3,6-dimethylnitrobenzene, 4-methylbenzaldehyde, and an aryl nitrate (Chiodini et al, 1993). 

CASRN 52664-04-7 molecular formula C16H23N3O2S2 FW 353.51 ChemicaPPhysical In the gas phase, MDTC reacted with OH, nitrate, and OH -1- nitrate radicals but not with ozone. One major product formed in the three reactions was tentatively identified as (CH3)2NC(0)SCH0. The relative reaction rates for the reaction of MDTC with OH and nitrate radicals were 1.33 x 10 " and 7.3 x 10cmVmolecule-sec, respectively (Kwok et al., 1992). 

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