Nitrate radical reactions with unsaturated

Atkinson R, Aschmann SM, Goodman MA. 1987. Kinetics of the gas-phase reactions of nitrate radicals with a series of alkynes, haloalkenes, and alpha, beta-unsaturated aldehydes. Int J Chem Kinet 19 299-308. 

Aldehydes are emitted directly into the atmosphere from a variety of natural and anthropogenic sources and are also formed in situ from the atmospheric degradation of volatile organic compounds (VOCs). The atmospheric fate of aldehydes is controlled by photolysis and reaction with hydroxyl (OH) or nitrate (NO3) radicals and, in the case of unsaturated compounds, reaction with ozone (Atkinson, 1994). The photolysis of aldehydes is of particular importance because it is a source of free radicals in the troposphere, and thus may significantly influence the oxidizing capacity of the lower atmosphere (Finlayson-Pitts and Pitts, 1986). 

The reaction of NO3 with unsaturated ethers proceeds by addition to the >C=C< double bond. Both steric and inductive effects are known to influence the reactivity of NO3 with unsaturated alcohols, e.g. 2-methyl-3-butene-2-ol is slightly less reactive than 1-butene. Unsaturated ethers are more reactive than unsaturated alcohols towards NO3. Comparison of the measured rate constants shows that, similar to the reaction with O3, the presence of the carbonyl group decreases the reactivity of NO3 toward the >C=C< double bond. The reaction of NO3 with unsaturated oxygenates proceeds by addition to either one of the carbon atoms of >C=C< double bond, preferentially to the most substituted radical. In the presence of NOx, the reaction may ultimately lead to organic nitrates among the first generation products. 

Evidence for the presence of the nitrate radical during night-time in the troposphere has led to considerable effort in establishing its role in atmospheric chemistry. Two main types of reactions of NO3 with volatile organic compounds have been identified, hydrogen atom abstraction and addition to unsaturated... 

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. 

Reaction with Allylic and Benzylic Electrophiles. The acyl radicals can be trapped with halogen- and silicon-based electrophiles. a -Allylation of a, -unsaturated ketones is done while using Mn(OAc)3 dihydrate and allyl bromide in refluxing benzene (eq 29). Better yields are usually observed for cyclopen-tenones compared to cyclohexenones. a -Benzylation is also possible using benzyl bromide as the electrophilic partner (eq 30). Both methods tolerate a range of substitution, including 8-alkoxy-a, -unsaturated ketones. It is possible to perform a sequential allylation/cyclization with an excess of allyltrimethylsilane (eq 31). Mn(OAc)3 offers good conversions, but the use of ceric ammonium nitrate (CAN) as co-oxidant improves yields. 

Using a relative rate method, Treves and Rudich (2(X)3) have measured rate coefficients for reactions of OH radicals with a series of C3-C6 hydroxyalkyl nitrates and two C4 unsaturated hydroxyl nitrates at atmospheric pressure and 296 2 K. Wangberg et al. (1996) have reported the rate coefficient for the OH reaction with 2-nitroxy-l-cyclopentanol also using a relative rate method. The rate coefficient values obtained in both studies are given in table Vlll-G-1. 

Noda, J., M. Hallquist, S. Langer, and E. Ljungstrom (2000), Products from the gas-phase reaction of some unsaturated alcohols with nitrate radicals, Phys. Chem. Chem. Phys., 2, 2555-2564. 

Grosjean, D., E.L. Williams II, and E. Grosjean (1993d), Gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH2=C(CH3)C(0)00N02, Int. J. Chem. Kinet, 25, 921-929. 

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