Nitrates radicals, oxidation with

Cresols degrade rapidly in air. Removal during the day is dominated by the reaction with hydroxyl radical (HO-), while nighttime removal is probably dominated by the nitrate radical. Reaction with other oxidants in air (e.g., ozone) will be much slower than reactions with hydroxyl or nitrate radical (Atkinson and Carter 1984). 

This work was intended to give information about non-photochemical processes affecting species that are involved in hydrocarbon oxidation and ozone formation, such as the hydrocarbons themselves or the active nitrogen compounds. The main part of the work was concerned with rates and products in nitrate radical reactions with various hydrocarbons. Some interest was also taken in purely inorganic reactions. 

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... 

Having shown that the enol silyl ethers are effective electron donors for the [D, A] complex formation with various electron acceptors, let us now examine the electron-transfer activation (thermal and photochemical) of the donor/ acceptor complexes of tetranitromethane and quinones with enol silyl ethers for nitration and oxidative addition, respectively, via ion radicals as critical reactive intermediates. 

Now, we will consider the major reactions of peroxynitrite with biomolecules. It was found that peroxynitrite reacts with many biomolecules belonging to various chemical classes, with the bimolecular rate constants from 10-3 to 10s 1 mol 1 s 1 (Table 21.2). Reactions of peroxynitrite with phenols were studied most thoroughly due to the important role of peroxynitrite in the in vivo nitration and oxidation of free tyrosine and tyrosine residues in proteins. In 1992, Beckman et al. [112] have showed that peroxynitrite efficiently nitrates 4-hydroxyphenylacetate at pH 7.5. van der Vliet et al. [113] found that the reactions of peroxynitrite with tyrosine and phenylalanine resulted in the formation of both hydroxylated and nitrated products. In authors opinion the formation of these products was mediated by N02 and HO radicals. Studying peroxynitrite reactions with phenol, tyrosine, and salicylate, Ramezanian et al. [114] showed that these reactions are of first-order in peroxynitrite and zero-order in phenolic compounds. These authors supposed that there should be two different intermediates responsible for the nitration and hydroxylation of phenols but rejected the most probable proposal that these intermediates should be NO2 and HO. ... 

Only a few examples exist for the intermolecular trapping of allyl radicals with alkenes68,69. The reaction of a-carbonyl allyl radical 28 with silyl enol ether 29 occurs exclusively at the less substituted allylic terminus to form, after oxidation with ceric ammonium nitrate (CAN) and desilylation of the adduct radical, product 30 (equation 14). Formation of terminal addition products with /ram-con figuration has been observed for reaction of 28 with other enol ethers as well. 

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... 

Chemical/Physical. The gas-phase reaction of ozone with pyridine in synthetic air at 23 °C yielded a nitrated salt having the formula [CeHsNHJ NOs (Atkinson et al., 1987). Ozonation of pyridine in aqueous solutions at 25 °C was studied with and without the addition of ferf-butyl alcohol (20 mM) as a radical scavenger. With tert-hniyX alcohol, ozonation of pyridine yielded mainly pyridine W-oxide (80% yield), which was very stable towards ozone. Without terf-butyl alcohol, the heterocyclic ring is rapidly cleaved forming ammonia, nitrate, and the amidic compound W-formyl oxamic acid (Andreozzi et al., 1991). 

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). 

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

All cresol isomers can be rapidly removed from environmental media. The dominant removal mechanism in air appears to be oxidation by hydroxyl radical during the day and nitrate radical at night, with half-lives on the order of a day. In water under aerobic conditions, biodegradation will be the dominant removal mechanism half-lives will be on the order of a day to a week. Under anaerobic conditions, biodegradation should still be important, but half-lives should be on the order of weeks to months. In soil under aerobic conditions, biodegradation is also important, but half-lives are less certain, although probably on the order of a week or less. 

At night, when the sun s radiation is minimal, the dominant VOC oxidant is nitrate radical (NO3 ). The chemistry initiated by NO3 differs from that initiated by HO radical in that NO3 prefers to react with unsaturated compounds via addition to one of the carbons of the 7t-system, rather than by hydrogen atom abstraction ... 

A high-level ab initio study of related reactions of alkyl nitrates (RO—NO2) at the G3 and B3LYP/6-311-I— -G(d,p) levels has revisited the reactions of alkyl peroxy radicals (ROO") with nitric oxide. Activation barriers for the isomerization of RO—ONO to RO—NO2 were found to be too high to account for the formation of alkyl nitrates... 

NO to form peroxynitrite (Eq. 18-62).559b Peroxynitrite, in turn, can react with the ubitquitous C02 to give C03 and N02 radicals.559c Peroxynitrite anion also reacts with metalloenzyme centers559"4 and causes nitration and oxidation of aromatic residues in proteins.559d e However, neutrophils contain active superoxide dismutases, and most of the superoxide that is formed is converted quickly to 02 and H202. 

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