Peroxy nitrate

Acetyl peroxy nitrate, stmcture, 103, 104 Acetylsaturejol, triplet oxygen cycloaddition, 202, 204... 

There is a second possible reaction path. In the absence of an excess of compound (1) it is possible that compounds (3) could undergo an intramolecular rearrangement of the peroxy-nitrate group to the nitrato complex (6). 

Peroxy nitric adds and organic peroxy nitrates are another precursors of free radicals, which may be introduced into polymers from polluted atmosphere. They produce both peroxy radicals and reactive nitrogen oxides (NO and N02) on decomposition. With alkyl peroxynitrates, decomposition proceeds via OO—N bond fission having activation energy 87 kJ/mol, their half-life being several seconds at 0 °C [12]. 

It is well established that the reaction of peroxy radicals with NO2 proceeds by a simple association mechanism in which an alkyl peroxy nitrate is formed. The exothermicity associated with formation of the RO2 - NO2 bond resides initially in the RO2NO2 molecule. Collisional deactivation is required to remove this excess energy. 

The RO2 - NO2 bond in alkyl peroxy nitrates is relatively weak (22-25 kcal mol-1) and the peroxy nitrate decomposes rapidly to reform the reactants [39]. For example, in 760 Torr of air the lifetimes of CH3O2NO2 at room temperature and - 10 °C are 0.6 and 51 s while for C2H5O2NO2 the corresponding lifetimes are 0.3 and 25 s [39]. 

As discussed in section 4, reaction of the peroxy radicals with N02 gives thermally unstable peroxy nitrates. Reaction with H02 gives hydroperoxides and possibly carbonyl compounds. Reaction with other peroxy radicals (R 02) gives alkoxy radicals, carbonyls, and alcohols. The alkoxy radicals will then either isomerize, react with 02, or decompose (see Sect. 3). Thus, the NO3 radical-initiated atmospheric degradation of alkenes leads to oxiranes (generally in small yield), nitrooxy hydroperoxides, nitrooxy carbonyls, and nitrooxyalcohols. For a detailed listing of products from individual alkenes the reader should consult Calvert et al. [55]. 

The benzyl radical formed in channel (a) behaves like an alkyl radical and in air adds O2 rapidly (within a xs) to give a benzyl peroxy radical which either reacts with HO2 radicals to give a hydroperoxide, with NO2 to give a thermally unstable peroxy nitrate, or with NO to give a 10-12% yield of benzyl nitrate and 88-90% yield of an alkoxy radical which then reacts with O2 to produce benzaldehyde [15,66]. 

The worst irritants in photochemical smogs are peroxyacyl nitrates, PAN. They produce singlet oxygen when they hydrolyze, and this may account for their biological action. Other objectionable components of photochemical smogs include aldehydes, organic hydroperoxides (ROOH), and peroxy nitrates. 

Dimethy lethyl peroxynitrate, 5ee tert-Butyl peroxy nitrate, 1663... 

Alkyl Nitrites, Peroxy Nitrates, and Other Organic Nitrates. 726... 

The PAN was isolated from the numerous side products by gas chromatography on preparatorysized columns and collected by cryogenic trapping. The PAN was then placed in large air canisters, diluted with zero air, and stored in a cold room for future use. Safety precautions are required with this method, because explosive accidents have been reported. The cause of the explosions is believed to be condensation of PANs in vacuum or pressure gauge systems. Like all nitrates, the peroxy nitrate PAN has explosive potential, and care must be taken when handling PAN on metal surfaces. The Stephens synthetic approach illustrated by Reaction 19.7 to Reaction 19.11 was quite successful, and a number of publications on the toxicity of PAN and its chemical and physical properties resulted from the use of the scheme. ... 

The large group of atmospheric species known as organic nitrates, of which the PANs are members, also contains alkyl nitrates, aryl nitrates, alkyl dinitrates, peroxy nitrates, multifunctional organic nitrates (hydroxynitrates, ketonitrates, etc.), and the sister species — the organic nitrites. All of... 

The peroxy nitrates are associated with the PANs, as these are formed by the addition reaction of RO2 and NO2 under high concentrations of NO2 ... 

Because of their short lifetimes at room temperature, the peroxy nitrates have been assumed not to act as key storage modes for peroxy radicals and NO2 in the lower atmosphere. At middle latitudes in the wintertime these may have hfetimes that approach days. Further, like the PANs these might be reformed to actively transport NO2 and peroxy radicals over long distances, depending upon the NO, hydroperoxy radical, and NO2 concentrations. With the possible exception of very cold air masses, these compounds are typically not present in significant concentrations in the troposphere because of rapid thermal decomposition to form NO2 and RO2. At room temperature they would be lost in samphng lines or during analysis. 

Because of these problems, neither the alkyl nitrites nor the peroxy nitrates will be dealt with here. We will focus here on the alkyl nitrates and their analysis. Other multifunctional organic nitrates (e.g., hydroxynitrates, ketonitrates) will be included with the alkyl nitrates, because these are determined with the same analytical methods. 

Alkyl peroxy nitrates ro2no2 CH302N02, methyl peroxynitrate... 

Peroxy radicals are stable with respect to reaction with the major constituents of the atmosphere. Their chemistry is dominated by reactions with peroxy radicals, HO2 and RO2, and with the nitrogen oxides, NO, NO2, and NO3. Two recent articles review the spectroscopy, kinetics, and reaction mechanisms of organic peroxy radicals [11,12], Three of the more important reaction channels are illustrated in Figure 1. The reaction with NO2 proceeds exclusively by addition to form the corresponding alkyl-peroxy nitrate. This reaction is generally not important in determining the end products of the degradation process due to the usually rapid dissociation rate of the peroxy nitrate however, it can be relevant to dynamical issues, because it sequesters N02-... 

The methylperoxy radical (and probably other peroxy radicals) reacts very rapidly with NO (4.41) relative to hydrogen abstraction (4.40), so only in very clean environments will the latter reaction occur to a significant extent (McFarland et al., 1979 Hanst and Gay, 1983). In polluted atmospheres, nitrogen oxides interfere with several other of the above reactions, leading to the formation of nitrate and peroxy-nitrate esters (see Section 4.A.4). 

Before a value for k2 can be extracted from the observed kinetics of the NO2 formation the impact of potential secondary reactions needs to be considered. Peroxy radicals, RO2, are known to react with NO2 to form peroxy nitrates [2, 3]. Hence, following the formation of NO2 fi om reaction (2), there is a competition between reactions (2) and (3) for the available RO2 radicals ... 

In air, alkyl or allyl macroradicals produced in reactions with NO can oxidise to give peroxide radicals. The reactions of the latter with NO result in relatively unstable peroxy nitrates similar to low-molecular peroxide radicals [15, 16] ... 

The reaction of perfluoroperoxide macroradicals also yields peroxy nitrate. In this case, the decomposition similar to (Equation 6.21) results in destruction of the macromolecule because the resultant alkoxyl radicals in fluorinated polymers cannot enter into the substitution reaction [18] ... 

However, in PTFE containing end peroxide radicals, no regeneration of these radicals after the removal of NO was observed, though the decomposition temperature was raised to 140 "C. Nevertheless, the reappearance of peroxide radicals in PTFE upon evacuating shows that the product of the R O reaction with NO is peroxy nitrate, and fluorinated compounds also exhibit the reversible reaction ... 

Hydrolysis of peroxy nitrate due to the possible presence of water vapour can also take place ... 

The conversion of peroxy nitrate can also occur upon storage of the sample in an atmosphere containing nitrogen oxides by the formal scheme ... 

When NO enters the reacting system, the initial peroxide radicals quantitatively convert into peroxy nitrate and [R O NO ]g = [R O lg. The regeneration process of peroxide radicals in vacuum should follow the equation ... 

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