Nitrate radical reaction with esters

As mentioned earlier, when NO concentration exceeds that of superoxide, nitric oxide mostly exhibits an inhibitory effect on lipid peroxidation, reacting with lipid peroxyl radicals. These reactions are now well studied [42-44]. The simplest suggestion could be the participation of NO in termination reaction with peroxyl radicals. However, it was found that NO reacts with at least two radicals during inhibition of lipid peroxidation [50]. On these grounds it was proposed that LOONO, a product of the NO recombination with peroxyl radical LOO is rapidly decomposed to LO and N02 and the second NO reacts with LO to form nitroso ester of fatty acid (Reaction (7), Figure 25.1). Alkoxyl radical LO may be transformed into a nitro epoxy compound after rearrangement (Reaction (8)). In addition, LOONO may be hydrolyzed to form fatty acid hydroperoxide (Reaction (6)). Various nitrated lipids can also be formed in the reactions of peroxynitrite and other NO metabolites. 

The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyon and his coworkers13,63 in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl forma-tion.68(0< > Apparently some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl,... 

The rate data for reaction of NO3 with aliphatic esters show that the presence of the ester group in an organic molecule has little influence on the reactivity compared to the parent alkane. The reactivity trends exhibited by the nitrate radical for reactions with alcohols, ethers and esters are similar to those shown for the analogous reactions of hydroxyl radicals. The major products identified from the NO3 radical-initiated oxidation of alcohols, ethers and esters under atmospheric conditions were esters, carbonyls and alkyl nitrates. Similar products arise from the reactions of OH radicals with these molecules under atmospheric conditions. 

A number of esters [10], ethers [11, 12] and alcohols [13] were investigated with respect to reactivity with nitrate radicals. Both absolute and relative rate methods were employed. Rate coefficients for the reaction of NO3 are given in Table 1. The rate coefficients for aliphatic esters may be predicted from available group reactivity factors for alkanes provided that formate carbonyl hydrogen atoms are treated as primary hydrogen atoms. The rate coefficients with temperature dependence for ethers and alcohols are valid between 268 to 363 K. 

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. 

Dinitrogen pentoxide reacts with alkanes in carbon tetrachloride at 0 °C via a radical mechanism to give nitration products which can include nitrate esters.Reactions of alkanes with dinitrogen pentoxide in nitric acid are complex and of little synthetic value. 1-Adamantyl nitrate is one of the products obtained from the photochemical irradiation of a solution of adamantane and dinitrogen pentoxide in methylene chloride. ... 

They acted on 2-nitratoethanol with chlorides of acrylic (a), methacrylic (b) and croionic (c) acids in the presence of cuprous chloride as a polymerization inhibitor. The radical polymerization was initiated by benzoyl peroxide in nitrogen atmosphere. It lasted 20 min at 100 C. In the absence of a catalyst polymerization occurred at 20 C in the course of a few days. This observation is in agreement with the finding reported in V ol. II, p. 19 that nitrate esters can catalyse polymerization reaction, contrary to C-nitro compounds (Chapter IV). 

The oxidation of 1-methoxycyclopropanol with iron(IIl) nitrate in methanol in the presence of but-3-en-2-one gives the 6-oxo ester in 30% yield.The mechanism may involve addition of a 2-(methoxycarbonyl)ethyl radical, obtained via iron(III) induced oxidation, to but-3-en-2-one resulting in an a-keto radical. A more effective and practical intermolecular addition of cyclopropanols to alkenes was recently performed in the presence of manganese(III) pyridine-2-carboxylate (Table 4)T 32 -phe reaction may proceed by way of (i) generation of 8-acylalkyl... 

Since the discovery of Binkley and Koholic, nitrate esters have been used as sources of alkoxyl radicals by treatment with either tributyltin hydride/AIBN or photolysis [16], These authors described the conversion of the nitrate ester derivative of d-allose into the inverted aleohol by a radical -fragmentation-recyclization reaction as shown (Eq. 27, Scheme 8) [16e,f[. 

The methylperoxy radical (and probably other peroxy radicals) reacts very rapidly with NO (4.41) relative to hydrogen abstraction (4.40), so only in very clean environments will the latter reaction occur to a significant extent (McFarland et al., 1979 Hanst and Gay, 1983). In polluted atmospheres, nitrogen oxides interfere with several other of the above reactions, leading to the formation of nitrate and peroxy-nitrate esters (see Section 4.A.4). 

In order to form the required cyanide and cyanate radicals, the C-N structure must already be present in the molecule. Nitro compounds are detected, but not nitrate esters, ammonia or nitrogen oxides. By taking part in the alkali reaction the cyanide radical receives an electron. Cyanide ions are formed, which react with other radicals to give neutral species. The electron released provides the detector signal. 

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