Carbonyl nitrate

The paper discusses two types of reaction involving metal complexes, and it is postulated that each proceeds by an initial free-radical step. In reactions between metal carbonyls and N2O4—NO2 mixtures, the nature of the product depends upon the phase in which the reaction is carried out. In the liquid phase, where the predominant equilibrium is N204 N0+ + NO3-, metal nitrates or carbonyl nitrates are formed in the gas phase, where the equilibrium is N2O4 2NO2/ nitrites or their derivatives are produced. Reactions of Mn2(CO) o Fe(CO)5, Co2(CO)3, and Ni(CO)4 are discussed. Anhydrous metal nitrates in which the nitrate group is covalently bonded to the metal have enhanced reactivity. This is believed to result from the dissociation M—O—N02 M—O + NO2 This can explain the solution properties of beryllium nitrates, and the vigorous (even explosive) reaction of anhydrous copper nitrate with diethyl ether. 

Under atmospheric conditions, the nitro-oxyalkyl peroxy radicals will probably form mainly the corresponding nitro-oxy alkoxy radicals. Thermal decomposition, yielding carbonyl compounds and NO2, and reaction with O2 giving carbonyl nitrates, appear to be the dominant reactions under most atmospheric conditions. The extent to which carbonyl nitrates can act as temporary reservoirs for NOx will largely depend on their photolysis rates or reactions with OH radicals. 

Combination of the available rate constant data with estimates of the atmospheric concentrations of O3, NO3 and OH indicates that the reaction of NO3 with substituted alkenes and terpenes may be the dominant tropospheric oxidation process for these species. Formation of carbonyl nitrates in the reactions could be important in the long-range transport of odd nitrogen. 

UV absorption spectra have been measured for the ketonitrates and dinitrates (LACTOZ 89). In the region of atmospheric interest (X > 270 nm) the absorption cross sections of the carbonyl nitrates are approximately a factor of 10 higher than those of the dinitrates. From the measured cross sections photolysis frequencies have been calculated for the organic ketonitrates and dinitrates. Although the photolysis frequencies represent upper limits the results indicate that photolysis will generally be somewhat more important than loss via reaction with OH radicals for saturated difunctional nitrates. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink. The product studies show that photolysis of ketonitrates/dinitrates will result in the re-release of NO2 and the formation of PAN-type compounds. 

In the investigation of products and intermediates from the reactions between NO3 and the alkenes (propene isobutene trans- and cis butene 2-methyl-2-butene 2,3-dimethyl-2-butene and isoprene) it was found that all of them followed a similar pattern. The build-up of organic nitrate bands (845, 1280 and 1667 cm ) and peroxynitrate bands (790,1300,1725 cm" ) were observed in the IR-spectra as showed in Fig. 2. The subsequent decay of the peroxynitrate bands was accompanied by a build-up of spectral features attributed to stable products (see Fig. 2). These stable products were identified as aldehydes, alcohol nitrates, carbonyl nitrates and dinitrates [3,4]. 

For the two investigated compounds with the chlorine atom substituted next to the double bond, the intensity of the nitroperoxy bands passed through a maximum while the nitroxy bands continued to increase during the course of the experiments. A carbonyl band at approximately 1750 cm was seen at the same time. This indicates that either a carbonyl nitrate compound or a nitrate and a carbonyl compound were formed through decomposition of the nitroperoxy nitrate intermediate. Small amounts of acetaldehyde and chloroacetaldehyde were found among the products formed from the reaction with l-chloro-2-butene. In the reaction with 3-chloro-l-butene, significant amounts of formaldehyde were formed. 

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). 

Na2Si03, Na4Si20s, gas phase reduction [11,15,19,21]. Generally, metal chloride salts (H2PtCl6, RuCls, NiCU, etc.) are used as metal precursors. As metal chloride salts may reduce the dispersion of nanoparticles (NPs) on support materials [21], a number of binary and ternary electrocatalysts have also been prepared by using chloride-free precursor salts such as carbonyl, nitrate, sulfite complexes, etc. [15,21]. NaBH4 and polyol reduction methods are repeatedly used [15,21-25]. Recently, the microwave assisted chemical reduction method has also been used to obtain better dispersion and reduce the particle sizes of metal catalysts [24-26]. 

They also detected Cio-dicarbonyl and hydroxydicarbonyl compounds, a Cio-carbonyl nitrate, and a Cio-hydroxycarbonylnitrate. They suggested that these might arise from abstraction at the 6-position (y to the carbonyl group) followed by a sequence of reactions involving competitive isomerization and reaction with O2 by the oxy radicals. 

The expected OH-initiated oxidation products are the bifunctional organic nitrates such as carbonyl nitrates, hydroxycarbonyl nitrates, dinitrates, and hydroxynitrates depending on the size of the initial alkyl nitrates and NOx concentrations. However, no direct product studies have been performed so far and the products remain speculative. 

Hydroxyalkyl nitrates are more reactive in the gas phase than alkyl nitrates and are more soluble in water. It is expected that hydroxynitrates are less-effective transporters of NO , than are the alkyl nitrates. On the other hand, the OH-initiated oxidation of hydroxyl nitrates may lead to long-lived carbonyl nitrates, which could play a role in the long-range transport of NOj. 

Table Vlll-H-I. Rate coefficients (fe, cm molecule s ) for the reaction of OH with carbonyl nitrates...

VIII-H-2. Summary of the Atmospheric Fate of Carbonyl Nitrates... 

Combining the rate coefficient values reported above and a diurnal average [OH] = 10 molecule cm provides an estimate of the atmospheric lifetime of carbonyl nitrates with respect to removal by reaction with OH in the range 3 to 30 days. Photolysis is also likely to be an important atmospheric loss mechanism. Wangberg et al. (1996) conclude that the photodecomposition in the troposphere is unimportant for tra 5 -2-hydroxy-cyclopentyl-1-nitrate (no significant absorption) but both 2-oxo-cyclohexyl-l-nitrate... 

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