Nitrate radical reaction with alkenes

B.6.2.2 Alkenes Hydroxyl and nitrate radicals as well as ozone can react with alkenes. Although hydrogen abstraction is possible with the two radicals, addition to the double bond is the preferred reaction ... 

There are many reports for nitration of alkenes using various nitrating agents, which proceeds via an ionic or radical addition process.49 Nitration of cyclohexene with acetyl nitrate gives a mixture of 3-and y-nitrocyclohexenes, 1,2-nitroacetate, and 1,2-nitronitrate. This reaction is not a simple ionic or radical process instead, [2+2] cycloaddition of nitryl cation is proposed.50... 

Iron(n) salts mediated the coupling of trialkylboranes with KSGN to give RSCN via a radical process.553,554 Stereochemically pure ( )-l-thiocyanato-alkenes or ( )-l-azide-alkenes were obtained from alkynes when hydro-boration with disiamylborane was followed by reaction with potassium thiocyanate or sodium azide in the presence of copper(n) nitrate, copper(n) acetate, and small amount of water in polar aprotic solvent (Equation (116)).555... 

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]. 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

Alkenes react with the nitrate radical (Atkinson et al. 2000). As in OH-alkene reactions, N03 adds to the double bond and H-atom abstraction is relatively insignificant ... 

TABLE 6.21 Rate Constants for the Reaction of Hydroxyl and Nitrate Radicals and Ozone with Alkenes... 

The fast reaction of NO3 radicals with alkenes was found to give substantial yields of bifunctional carbonyl-nitroxy products and the mechanism of their formation is expected to be relevant also for the conditions of the troposphere. Studies performed by other workers [12] have shown that such organic nitrates may contribute to the atmospheric transport of NOx by acting as reservoirs, releasing NOx by their degradation in the atmosphere, but bifiinctional nitrates may also be subject to fast removal by wet deposition. 

Correlations between rate parameters and calculated molecular properties in the reaction of the nitrate radical with alkenes,... 

Nitrate radicals (NO3) are formed by the reaction of O3 and NO2 (Sect. 5.4.2) and play an important role in atmospheric chemistry at nighttime in polluted air. NO3 has an absorption spectrum in the visible region as seen in Sect. (4.2.4) so that daytime concentration is very low since it is easily photodecomposed by sun light. Simultaneously, since the reaction rate constant of NO3 with NO is large, it returns easily to NO2 by NO so that its concentration near NO sources is also very low. NO3 reacts with alkenes and aldehydes to form dinitrates and OH/HO2 radicals at nighttime. Rate constants of fundamental reactions of atmospheric NO3 and related N2O5 are cited in Table 5.6. 

Reaction Scheme 7.2 summarizes the reaction mechanism for 1-butene (l-C4Hg) as an example of alkenes. The hydroxyalkyl radicals formed by the pathways (a) and (b) is a kind of alkyl radicals mentioned in the previous Sect. (7.2.2), and exclusively forms hydroxyperoxy radicals by the reaction with O2 in the atmosphere. From the hydroxyperoxy radicals, oxyradicals (hydroxybutoxy radicals) and NO2 (pathways (d), (k)), and partially hydroxybutyl nitrate (pathways (e), (1)) are produced by the reaction with NO as in the case of alkylperoxy radicals described in the previous paragraph. The yields of hydroxylalkyl nitrates are 2-6 % for C4-C6 alkenes (O Brien et al. 1998), which is about half of those for alkyl nitrates from the alkoxy radicals. Hydroxy alkoxy radicals formed in pathways (d) and (k) are known to follow the three reaction pathways, unimolecular decomposition ((g), (n)), H-atom abstraction by O2 ((h), (o)), and dihydroxyl radical formation by isomerization (p), corresponding to reactions (7.25), (7.24) and... 

Perez-Casany, M.P., Nebot-Gil, I., Sanchez-Marin, J. Ab initio study on the mechanism of tropospheric reactions of the nitrate radical with alkenes propene. J. Phys. Chem. A 104,... 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

Meldrum s acid, like other 1,3-dicarboxyl compounds, was amenable to radical reactions at C-5. The radical reaction between Meldrum s acid benzyl alkyl ethers mediated by InCl3/Cu(OTf)2 has been reported to proceed regioselectively at the benzylic position of the ether moiety (Scheme 35) <2006AGE1949>. Radical reaction of Meldrum s acid and alkenes was carried out with 2equiv of ceric ammonium nitrate (CAN) to give the a-carboxy-lactones which were subsequently subjected to decarboxylative methylenation affording the a-methylene lactones in 35-50% yield (Scheme 35) <2006SL1523>. 

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. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

The reaction of dinitrogen tetroxide with alkenes generally gives 1,2-dinitro compounds, fi-ni-tro nitrites and /5-nitro nitrates, often as mixtures, by a radical mechanism (Section 7.2.1.7). However, a /5-nitroso nitrate was obtained by the heterolysis (NO NOf) of dinitrogen tetroxide and ionic addition to 2,3-dimethyl-2-butene71. 

The reaction of alkenes with dinitrogen tetroxide, following a radical mechanism, generally affords mixtures of 1,2-dinitro compounds, /(-nitro nitrites and jS-nitroso nitro compounds. By oxidation of /(-nitro nitrites with dinitrogen tetroxide itself or oxygen, /(-nitro nitrates are produced11 111. 

Only a few examples exist for the intermolecular trapping of allyl radicals with alkenes . The reaction of ot-carbonyl allyl radical 28 with silyl enol ether 29 occurs exclusively at the less substimted allylic terminus to form, after oxidation with ceric ammonium nitrate (CAN) and desilylation of the adduct radical, product 30 (equation l4). Formation of terminal addition products with frows-configuration has been observed for reaction of 28 with other enol ethers as well. 

---