Hydroperoxy nitrate

As seen in Reaction Scheme 7.3, in the NO3 and alkene reactions epoxy alkanes (also called epoxides or oxiranes), hydroperoxy nitrates, carbonyl nitrates and dinitrates are produced characteristically (Bandow et al. 1980 Kwok et al. 1996a Calvert et al. 2000), and some of them have been detected in the polluted atmosphere (Schneider et al. 1998). Recently, reactions of NO3 with alkenes are interesting from the view point of organic aerosol formation (Gong et al. 2005 Ng et al. 2008). 

Metal ions play an important role in several of these oxidative reactions as well as in biological dioxygen metabolism. As an example, copper(II) acetate and hydrogen peroxide have been used to produce a stable oxidizing agent, hydroperoxy copper(II) compound. The same oxidation system is also obtained from copper(II) nitrate and hydrogen peroxide (Eq. 1) [103] but requires the neutralization of ensuing nitric acid by potassium bicarbonate to maintain a pH 5. 

The branching ratio shown here for the production of the organic nitrate is based on reference 65. Both of the organic products still contain one double bond, so further oxidation is likely. The alkoxy radical produced in the first step rapidly decomposes methylvinylketone and formaldehyde are produced, as well as a hydroperoxy radical ... 

The fate of the organic nitrate peroxy radical produced in reaction 14 is probably oxidation of NO to N02 and then decomposition, yielding acetyl nitrate, formaldehyde, and a hydroperoxy radical as shown in reactions 15 and 16. 

Triphenyl-4,4-dimethyl-5-hydroperoxy-4,5-dihydro(3H)pyrazole, 3841 Triphenyllead nitrate, 3753... 

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. 

The organic peracids and peroxides are produced by the same chemistry which forms the PANs and the alkyl nitrates the alkyl nitrates and PANs are formed from peroxyacyl radicals (RCO3) and peroxy radicals (RO2) under high-NOx conditions, whereas the peracids and peroxides are formed under low-NO conditions through reactions with hydroperoxy radical ... 

Under relatively low NOx conditions in the atmosphere, a part of alkyl peroxy radicals, and hydroxyalkyl peroxy radicals react with HO2 to give hydroperoxy butane (pathways (f), (k)), and hydroxyhydroperoxy butane (pathway (q)). Thus, in oxidation reactions of alkane in the atmosphere, hydroperoxides, hydoxyhydor-peroxides, and hydroxyalkyl nitrate, could also be produced in addition to the normal aldehydes, ketones and alkyl nitrates. 

The direct use of nitric oxide (NO) reactions to identify and quantify hydroxyl (OH) and/or hydroperoxy (OOH) groups is complicated by the formation of equimolar mixtures of nitrates (with absorption bands at 1630, 1302, 1290, 1278 and 860 cm ) and nitrites (with a strong absorption band at 1645, and weak bands at 780-760 cm " ) ... 

The use of NO and sulphur tetrafluoride (SF4) gas treatments allows more precise identification and quantification of hydroxyl (OH) and hydroperoxy (OOH) groups (as nitrites and nitrates, respectively, after NO reaction) and carboxylic acids (after SF4 treatment to produce acid fluorides) (cf. section 10.17.1.5) and ketones (after removal of the overlapping acid absorptions and hydrogen-bonding effects with —OH groups by SF4 reactions) [362]. The NO reaction products are particularly informative because of their intense absorptions (up to 4-7 times stronger than those of the original OH species) and because primary, secondary and tertiary products have different IR absorptions [362]. 

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