Nitrate free radicals, generation

Tris[trinitratocerium(lV)] paraperio- 10.1. Generation of nitrate free radicals 364... 

The NOs- radicals can also be generated by flash photolysis of CAN in acetonitrile (Del Giacco et al., 1993). These photochemically produced nitrate free radicals have been used to study the one-electron oxidation of methylbenzenes. Depending on the oxidation potential of the substrate, radical cations or benzyl-type neutral radicals were formed. Formation of radical cations was observed for most of the methylbenzene derivatives that were studied, whereas formation of the benzyl radical was observed with toluene and with ortho- and meta-xylene. This reaction is not useful for synthetic applications. The reactivity of propellane C-C bonds towards free nitrate radicals photochemically generated from ammonium hexanitrato-eerate(IV) in acetonitrile was studied from both theoretical and experimental points of view (Fokin et al., 2000). Baciocchi and coworkers reported that the photochemical reaction of CAN in acetonitrile with cyclohexene, 1-octene and styrene derivatives leads to the formation of 1,2-dinifrate adducts in high yields (scheme 65) (Baciocchi et al., 1988b). 

The additives for improving the cetane number, called pro-cetane, are particularly unstable oxidants, the decomposition of which generates free radicals and favors auto-ignition. Two families of organic compounds have been tested the peroxides and the nitrates. The latter are practically the only ones being used, because of a better compromise between cost-effectiveness and ease of utilization. The most common are the alkyl nitrates, more specifically the 2-ethyl-hexyl nitrate. Figure 5.12 gives an example of the... 

This technique is based in the fact that when cellulose is oxidized by ceric salts such as ceric ammonium nitrate Ce(NH4)2(N03)6 free radicals capable of initiating vinyl polymerization are formed on the cellulose. However, the possibility remains that the radical formed is an oxygen radical or that the radical is formed on the C-2 or C-3 instead of the C-6 carbon atom. Another mechanism, proposed by Livshits and coworkers [13], involves the oxidation of the glycolic portion of the an-hydroglucose unit. Several workers [14,15], however, have found evidence for the formation of some homopolymer. In the ceric ion method free radicals are first generated and are then capable of initiating the grafting process [16-18]. 

Generation of radicals by redox reactions has also been applied for synthesizing block copolymers. As was mentioned in Section II. D. (see Scheme 23), Ce(IV) is able to form radical sites in hydroxyl-terminated compounds. Thus, Erim et al. [116] produced a hydroxyl-terminated poly(acrylamid) by thermal polymerization using 4,4-azobis(4-cyano pentanol). The polymer formed was in a second step treated with ceric (IV) ammonium nitrate, hence generating oxygen centered radicals capable of starting a second free radical polymeriza-... 

The major limitation of nitrate therapy is the development of tolerance with continuous use. The loss of anti-anginal effects may occur within the first 24 hours of continuous nitrate therapy. While the cause of tolerance is unclear, several mechanisms have been proposed. These include depletion of the sulfhydryl groups necessary for the conversion of nitrates to nitric oxide, activation of neurohormonal systems, increased intravascular volume, and generation of free radicals that degrade nitric oxide. The most effective method to avoid tolerance and maintain the anti-anginal efficacy of nitrates is to allow a daily nitrate-free interval of at least 8 to 12 hours. Nitrates do not provide protection from ischemia during the nitrate-free period. Therefore, the nitrate-free... 

Radiation-induced substitution reactions have been reviewed by Wilson (1972) with examples of nitration, nitrosation, sulfochlorination, and others. These generally proceed by a free-radical mechanism. The free radicals are generated by the action of radiation on the reagent, which is present in large excess—for example,... 

Protein tyrosine residues constitute key targets for peroxynitrite-mediated nitrations. Attack of various free radicals (ONOO-, N02 ) upon tyrosine generates 3-nitrotyrosine, which can be measured immunologically or by GC/MS or HPLC techniques. The detection of 3-nitrotyrosine was considered a biomarker of peroxynitrite action in vivo. Similarly, attack of HOC1 and HOBr on tyrosine generates chlorotyro-sine and bromotyrosine, respectively, both of which are measured most accurately by GC-MS. 

Manevich Y, Held KD, Biaglow JE (1997) Coumarin-3-carboxylic acid as a detector for hydroxyl radicals generated chemically and by gamma radiation. Radiat Res 148 580-591 Maples KR, Johnson NF (1992) Fiber-induced hydroxyl radical formation correlation with mesothelioma induction on rats and humans. Carcinogenesis 13 2035-2039 MarkG, Korth H-G, Schuchmann H-P, von Sonntag C (1996) The photochemistry of aqueous nitrate revisited. J Photochem Photobiol A Chem 101 89-103 Maskos Z, Rush JD, Koppenol WH (1990) The hydroxylation of the salicylate anion by a Fenton reaction and v-radiolysis a consideration of the respective mechanisms. Free Rad Biol Med 8 153-162... 

Nitrate/nitrite-induced methemoglobinemia is an important event that generates free radicals (Kohn et al., 2002). It is well known that nitrate/nitrite could enhance... 

Dichloropyridazine can be successfully alkylated and hydroxyalkylated by free radicals (Scheme 26). 4-t-Butyl-3,6-dichloropyridazine is prepared in high yield <880PP117>, and in a novel radical hydroxyalkylation, hydroxy-t-butyl radicals generated in situ from 2,2-dimethyl-1,3-pro-panediol react to give the 4-hydroxy-t-butyl derivative (76), along with some of the fused dihydro-furopyridazine byproduct the product (76) can be obtained pure in 55-60% yield by recrystallization. In the latter 3,6-dichloropyridazine reaction, trifluoroacetic acid and silver nitrate both catalyse hydrolysis of the dichloropyridazine substrate, but if the acid is omitted, or the quantity... 

Side-chain halogenated amino acid derivatives are reduced, deuterated, allylated and alkylated with stannanes and related reagents in free-radical processes [53]. Other side-chain functional groups may also be manipulated to produce amino acid radicals [8, 54-58], and, in particular. Barton decarboxylation of aspartate and glutamate derivatives has been applied in this manner (Scheme 8) [55]. Related procedures have been developed to generate amino acid radicals by dehydrox-ylation of hydroxy amino acid derivatives [56]. Hydroxy amino acid derivatives may also be converted to nitrate esters, from which the corresponding alkoxy radi-... 

The most effective additives in PAHs reduction were the nitrates. The following explanation of their effectiveness was offered. When heated, the nitrates generate nitric oxide (NO), an odd-electron componnd, capable of scavenging free radicals thermally generated from tobacco components... 

Addition of nitrate to the tobacco blend significantly reduced MSS yields of tar, PAHs, and phenols. The odd-electron compound NO generated during the smoking process interrupted the free radical mechanism of formation of PAHs [Hoffmann and Wynder (1797)]. The % tumor-bearing animals (%TBA) of the resulting CSC was also reduced by about 80%. On the basis of these results, nitrate addition or use of high-nitrate tobaccos was proposed. 

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