Isoprene nitrate

Isoprene [78-79-5] (2-methyl-1,3-butadiene) is a colorless, volatile Hquid that is soluble in most hydrocarbons but is practically insoluble in water. Isoprene forms binary azeotropes with water, methanol, methylamine, acetonitrile, methyl formate, bromoethane, ethyl alcohol, methyl sulfide, acetone, propylene oxide, ethyl formate, isopropyl nitrate, methyla1 (dimethoxymethane), ethyl ether, and / -pentane. Ternary azeotropes form with water—acetone, water—acetonitrile, and methyl formate—ethyl bromide (8). Typical properties of isoprene are Hsted in Table 1. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reactions Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Polymerization is accelerated by heat and exposure to oxygen, as well as the presence of contamination such as iron rust. Iron surfaces should be treated with an appropriate reducing agent such as sodium nitrate, before being placed into isoprene service Inhibitor of Polymerization Tertiary butyl catechol (0.06 %). Di-n-butylamine, phenyl-beta-naphthylamine andphenyl-alpha-naphthylamine are also recommended. 

The formation of peroxyacetyl nitrate from isoprene (Grosjean et al. 1993a) and of peroxy-propionyl nitrate (Grosjean et al. 1993b) from ctT-3-hexen-l-ol that is derived from higher plants, illustrate important contributions to atmospheric degradation (Seefeld and Kerr 1997). 

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. 

Chen, X., D. Hulbert, and P. B. Shepson, Measurement of the Organic Nitrate Yield from OH Reaction with Isoprene, J. Geophys. Res., 103, 25563-25568(1998). 

Skov, H J. Hjorth, C. Lohse, N. R. Jensen, and G. Restelli, Products and Mechanisms of the Reactions of the Nitrate Radical (N03) with Isoprene, 1,3-Butadiene and 2,3-Dimethyl-l,3-butadiene in Air, Atmos. Environ., 26A, 2771-2783 (1992). 

Skov, H Th. Benter, R. N. Schindler, J. Hjorth, and G. Restelli, Epoxide Formation in the Reactions of the Nitrate Radical with 2,3-Dimethyl-2-butene, cis- and trans-2-Butene, and Isoprene, Atmos. Environ., 28, 1583-1592 (1994). 

Acetic acid (CH3COOH) ACAC Nitrate of isoprene ISNT... 

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 ... 

The further decomposition of acetyl nitrate in the atmosphere has not been studied. The oxidation of isoprene by the hydroxyl radical proceeds via repeated steps of OH addition across the double bond, followed by addition of 02 to form a peroxy radical. The peroxy radical then either oxidizes NO to N02 or adds NO to form an organic nitrate. The alkoxy radical produced in the former step underwent decomposition to form both stable and reactive products. A number of possible pathways exist for forming presumably stable organic nitrates (bold in reactions 7 through 16). 

In addition to being oxidized by the hydroxyl radical, alkenes may react with the N03 radical as has been described by several investigators (52, 56, 66). Listed in Table I are some of the organic nitrates that have been predicted to be produced via reaction of OH and N03 with isoprene and pro-pene. Analogous compounds would be expected from other simple alkenes and from terpenes such as a- and (3-pinene. Other possible organic nitrates may be produced via the oxidation of aromatic compounds (53, 54) and the oxidation of carbonaceous aerosols (67). Quantitative determination of these species has not been made in the ambient atmosphere. 

Kleno, J. and Wolkoff, P. (2004) Changes in eye blink frequency as a measure of trigeminal stimulation by exposure to limonene oxidation products, isoprene oxidation products and nitrate radicals. International Archives of Occupational and Environmental Health, 77 (4), 235-43. 

As Barr et al. (2003) pointed out, the importance of such emissions is determined mainly by their impact on the three processes taking place in the atmosphere. The first consists in that such NMHCs as isoprene form in the course of carboxylization in plants and contribute much thereby to the formation of biospheric carbon cycle. The second process is connected with NMHCs exhibiting high chemical activity with respect to such main oxidants as hydroxyl radicals (OH), ozone (03), and nitrate radicals (N03). Reactions with the participation of such components result in the formation of radicals of alkylperoxides (R02), which favor efficient transformation of nitrogen monoxide (NO) into nitrogen dioxide (N02), which favors an increase of ozone concentration in the ABL. Finally, NMHC oxidation leads to the formation of such carbonyl compounds as formaldehyde (HCHO), which stimulates the processes of 03 formation. Finally, the oxidation of monoterpenes and sesquiterpenes results in the intensive formation of fine carbon aerosol with a particle diameter of <0.4 pm... 

The nitrate radical has a range of reactivity towards VOCs. The nitrate radical is highly reactive towards certain unsaturated hydrocarbons such as isoprene, a variety of butenes and monoterpenes, as well as reduced sulfur compounds such as dimethylsulfide (DMS). In the case of DMS, if the NO2 concentration is 60% that of DMS then NO3 is a more important oxidant than OH for DMS in the MBL. In general, NO3 abstraction reactions of the type... 

With barium nitrate alone as the oxidizer the composition does not burn quickly and creates a large amount of ash. To avoid this, potassium perchlorate is added to the composition. The chlorinated isoprene rubber intensifies the green colour of the flajne. 

Isoprene is a eonjugated diene (2-methyl-buta-1,3-diene), volatile and hardly soluble in water under normal pressure it boils at 34 C (Merck, 1999) and dissolves up to 1.47x10 M at 21.5 C, with a Henry s constant of 0.027 mole kg atm at 25 C (NIST, 2001). Isoprene is a metabolite in plants, microbes, animals and humans, and a major biogenic trace compound emitted to the atmosphere. It is very reactive towards atmospheric gas-phase oxidants such as hydroxyl and nitrate radicals or ozone. At higher concentrations, 220 - 7000 ppm, it is carcinogenic to rodents and possibly carcinogenic to humans (Melnick and Sills, 2001). 

Potentially hazardous reactants. Spontaneons polymerizations with exothermic heat generation inclnde styrene, snbstitnted styrene, vinyl chloride, vinyl pyridine, acrylonitrile, bntadience, isoprene cyclopentadience, and methyl isocyanate reactions involving peroxides as illnstrated in Table 16.17, azides, perchlorates, or nitro componnds and decompositions, nitrations, oxidations, alkylations, aminations, combnstions, condensations, diazotizations, halogenations, or hydrogenations. 

Biogenic hydrocarbons are principally emitted by trees. Isoprene and a- and /3-pinene are the most abundant biogenic hydrocarbons which are emitted (Dimitriades, 1981) (see Fig. 7). The rate constants of the reactions of the biogenics with OH, ozone, and nitrate radicals have been well investigated (Atkinson, 1991 Atkinson et ai, 1990). However, limited data are available concerning the products of biogenic reactions in the atmosphere. 

In the presence of NO, the OH radical photooxidation of isoprene leads to methacrolein O = CHC(CH3) = CH2, methyl vinyl ketone CH2 = CHC(0)CH3, and 3-methylfuran, in yields of 35.5%, 25%, and 5.1%, respectively (Paulson et al., 1991a). Similar yields were obtained by Gu et al. (1985) and Tuazon and Atkinson (1990). A variety of other species, including organic nitrates and multisubstituted hydrocarbons, are also possible products. The yields of these remaining products have not been reported in the literature. Clearly, further work is needed to account for the remaining carbon. 

Limited product data are available for the nitrate radical reaction with isoprene and a- and /3-pinene. For the isoprene reaction, Barnes et al. (1990) determined molar yields of total nitrates of 80%, CO of 4%, and formaldehyde of 11%. Methacrolein was also detected, but an accurate product yield could not be determined. Additional work with a- and /3-pinene was not conclusive. Although nitrate features were observed as initial reaction products, these compounds quickly transferred into aerosols, thus preventing identification via the methods employed in the study (FTIR spectroscopy). 

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