Organic nitrates formation

Kasibhatla, P., W. L. Chameides, B. Duncan, M. Houyoux, C. Jang, R. Mathur, T. Odman, and A. Xiu, Impact of Inert Organic Nitrate Formation on Ground-Level Ozone in a Regional Air Quality Model Using the Carbon Bond Mechanism 4, Geophys. Res. Lett., 24, 3205-3208 (1997). 

A second pathway in this reaction results in organic nitrate formation (9, 17, 18). The size and structure of the organic group controls the yield of reaction 16b relative to 16a. 

NO-sensitive GC represents the most important effector enzyme for the signalling molecule NO, which is synthesised by NO synthases in a Ca2+-dependent manner. NO-sensitive GC contains a prosthetic heme group, acting as the acceptor site for NO. Formation of the NO-heme complex leads to a conformational change, resulting in an increase of up to 200-fold in catalytic activity of the enzyme [1]. The organic nitrates (see below) commonly used in the therapy of coronary heart disease exert their effects via the stimulation of this enzyme. 

Nitric acid also undergoes reactions with organic compounds wherein the acid serves neither as an oxidizing agent nor as a source of hydrogen ions. The formation of organic nitrates by esterification (O-nitration) involves reaction with the hydroxyl group ... 

Feelisch, M., Noack, M., Correlation between nitric oxide formation during degradation of organic nitrates and activation of guanylate cyclase. Eur. J. Pharmacol. 139 (1987), p. 19-30... 

W. B., Glutathione S-transferases in the formation of cyanide from organic thiocyanates and as an organic nitrate reductase. Biochem. Biophys. Res. Commun. 64 (1975), p. 501—506... 

However, a few thiols (cysteine, N-acetylcysteine and thiosalicylic acid) also react with organic nitrates to release NO by another process that is difficult to discern. It could be that the nitrite reacts with a thiol to give an S-nitrosothiol, a ready source of NO, but nitrosation is unlikely to occur at biological pHs. Another possible route to NO involves formation of a thionitrate by trans-esterification [59] (Eq. (12)). This species could then decompose to give NO via an intermediate sulfenyl compound [60] (Eq. (13)). 

Fig. 9.1. Simplified reaction mechanisms in the hydrolytic decomposition of organic nitrates. Pathway a Solvolytic reaction (Reaction a) with formation of a carbonium ion, which subsequently undergoes SN1 addition of a nucleophile (e.g., HO ) (Reaction b) or proton E1 elimination to form an olefin (Reaction c). Pathway b HO -catalyzed hydrolysis (,SN2). Pathway c The bimolecular carbonyl-elimination reaction, as catalyzed by a strong base (e.g., HO or RO ), which forms a carbonyl derivative and nitrite.

Field studies suggest that the nitrate radical reaction can also be a major contributor to isoprene decay at night, as well as contributing to the formation of organic nitrates in air. For example, Starn et al. (1998b) found that when the product of N02 and 03 (which form N03) was high in a forested region in the southeastern United States, isoprene often decayed rapidly at dusk. This reaction of N03 with isoprene was estimated to be the major sink for N03 under some conditions in this area. 

Plumes from biomass burning can also have unique signatures. For example, organics, ammonium, potassium, sodium, nitrate, nitrite, sulfate, chloride, phosphate, elemental carbon, and the anions of organic acids (formate, acetate, oxalate, etc.) have all been measured in particles in the plumes from burning vegetation (e.g., see Cofer et al., 1988 Andreae et al., 1988 and Artaxo et al., 1994). 

Since then, a number of studies of model systems have confirmed that dialkenes, cyclic alkenes, and aromatics form substituted monocarboxylic acids, dicar-boxylic acids, and organic nitrates in the condensed phase (e.g., see O Brien et al., 1975a Grosjean and Friedlander, 1979 Dumdei and O Brien, 1984 Izumi and Fukuyama, 1990 and Forstner et al., 1997a, 1997b). For example, Table 9.21 shows the products identified in particles formed in the 1-octene- and 1-decene-NO,-ambient air systems. In both bases, only 40% of the total particle mass could be identified, and the yields shown in Table 9.21 are those relative to the total identified compounds. That is, the absolute product yields are about factor of 2.5 larger. As expected from the known oxidation mechanisms (see Chapter 6.E), heptanal and heptanoic acid are the major condensed-phase oxidation products of 1-octene and nonanal and nonanoic acid from 1-decene (see Problem 4). The mechanism of formation of the fura-nones, which are formed in relatively high yields, is not... 

Action of DPhA on NC and on other organic nitrates was examined in France by several investigators such as Demougin Landon (Ref 14), Muraour (Ref 15) and others. Muraour found that NC is attacked in storage by NC and by other nitric esters (such as PETN) with formation of mono- and poly-nitroderivatives of DPhA. When DPhA was replaced by Centralite 1 (N,N -diethyl-N,N -diphenylurea), which has no mobile H, no reaction occurred, and for this reason Muraour preferred Centralite to DPhA. 

Measurements of these relatively minor species will not only complete the budget of NO, but will also indicate if our understanding of the hydrocarbon oxidation schemes in the atmosphere is complete. The organic nitrates that completed the NO, budget in the example in Figure 9 arose primarily from the oxidation of the naturally emitted hydrocarbon, isoprene (2-methylbutadiene). To demonstrate the oxidation mechanisms believed to be involved in the production of multifunctional organic nitrates, a partial OH oxidation sequence for isoprene is discussed. The reaction pathways described are modeled closely to those described in reference 52 for propene. The first step in this oxidation is addition of the hydroxyl radical across a double bond. Subsequent addition of 02 results in the formation of a peroxy radical. With the two double bonds present in isoprene, there are four possible isomers, as shown in reactions 2-5 ... 

Nitric oxide generation from L-arginine and nitric oxide donors and the formation of cGMP. L-NMMA inhibits nitric oxide synthase. Some of the nitric oxide donors such as furoxans and organic nitrates and nitrites require a thiol cofactor such as cysteine or glutathione to form nitric oxide. 

As discussed in the previous sections reaction of NO3 radicals with organic compounds results in the formation of HNO3 and organic nitrates. In the stratosphere CIO radicals react with N02 to give C10N02 which undergoes hydrolysis. 

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