Free-radical reactions nitration

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

Nitromethane was first prepared in 1872 by Kolbe, and is produced commercially by high-temperature vapour-phase nitration of propane. The process, which uses nitric acid as the nitrating agent, is based on a free-radical reaction in which the active species is the NO2 radical (Markofsky, 1991 Angus Chemical Co., 1998). 

The usual way to achieve heterosubstitution of saturated hydrocarbons is by free-radical reactions. Halogenation, sulfochlorination, and nitration are among the most important transformations. Superacid-catalyzed electrophilic substitutions have also been developed. This clearly indicates that alkanes, once considered to be highly unreactive compounds (paraffins), can be readily functionalized not only in free-radical from but also via electrophilic activation. Electrophilic substitution, in turn, is the major transformation of aromatic hydrocarbons. 

The features of initiation of free radical reactions in polymers by dimers of nitrogen dioxide are considered. The conversion of planar dimers into nitrosyl nitrate in the presence of amide groups of macromolecules has been revealed. Nitrosyl nitrate initiates radical reactions in oxidative primary process of electron transfer with formation of intermediate radical cations and nitric oxide. As a result of subsequent reactions, nitrogen-containing radicals are produced. The dimer conversion has been exhibited by estimation of the oxyaminoxyl radical yield in characteristic reaction of p-benzoquinone with nitrogen dioxide on addition of aromatic polyamide and polyvinylpyrrolidone to reacting system. The isomerisation of planar dimers is efficient in their complexes with amide groups, as confirmed by ab initio calculations. 

Several papers appeared after the pioneer work of Mine and co-workers (Vol. I, p. 126). Papers by Chernova and co-workers [S3] and Sugimoto and co-workers [54] have shown that even dilute nitric acid (0.1-1.7 N) can nitrate aromatic compounds when subjected to gamma radiation from Co °. Benzene yielded nitrobenzene and p-nitrophenol as the result of free radical reactions. Nitric acid is decomposed by radical mechanism according to equation [55] ... 

Free-radical reactions. Silver nitrate, sodium persulfate, and iron(III) nitrate constitute an oxidizing system that degrades carboxylic acids to radicals. Adding these reactive intermediates to radical acceptors such as methyl vinyl ketone, acrylic esters, and acrylonitrile initiates synthetically useful processes. Monoamides of oxalic acid undergo oxidative degradation by (NH )2SjOg in the presence of AgNOj-Cu(OAc)2 to afford isocyanates in a biphasic system (11 examples, 45-87%). ... 

Nitration reactions can be divided into ionic, radical ion, mA free radical reactions. Within ionic nitrations one can differentiate the more predominant electrophilic nitrations (proceeding through the nitronium ion, NOJ, or some of its polarized —X carriers) and nucleophilic nitrations... 

A free radical reaction involving nitration of decane is carried out in two sequential reactor stages, each of which operates like a continuous stirred-tank reactor (CSTR). Decane and nitrate (as nitric acid) in varying amounts are added to each reactor stage, as shown in Fig. 19.4. The reaction of nitrate with decane is very fast and forms the following products by successive nitration DNO3, D(N03)2, D(N03)3, D(N03)4, and so on. The desired product is DNO3, whereas dinitrate, trinitate, etc., are undesirable products. 

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