Nitric acid with aromatic rings

Catalyzes the reaction of nitric acid with aromatic rings to yield nitroarenes (Section 16.2). 

There are several reaction systems that are capable of effecting nitration. A major factor in the choice of reagent is the reactivity of the aromatic ring to be nitrated. Concentrated nitric acid can effect nitration, but it is not nearly so reactive as mixtures of nitric acid with sulfuric acid. In both media, the active nitrating species is the nitronium ion. A variety of physical measurements provide evidence for the existence of this species and permit estimation of its concentration under some conditions. In concentrated sulfuric acid, the dissolution of nitric acid results in the formation of nearly 4 ions per nitric acid molecule, as determined by freezing-point depression ... 

Nitration introduces a nitro group (— NO ) onto an aromatic ring. Electrophilic aromatic substitution requires nitric acid (HNOj), with sulfuric acid as a catalyst. Nitronium ion, (NO ), is the electrophile. It forms in two steps by the reaction of nitric acid with sulfuric acid. 

Miscellaneous Reactions. Aromatic sulfonic acid derivatives can be nitrated using nitric acid [52583-42-3] HNO, ia H2SO4 (19). Sultones may be treated with hydrazine derivatives to give the corresponding ring-opened sulfonic acid (20). 

Aromatic Ring Reactions. In the presence of an iodine catalyst chlorination of benzyl chloride yields a mixture consisting mostly of the ortho and para compounds. With strong Lewis acid catalysts such as ferric chloride, chlorination is accompanied by self-condensation. Nitration of benzyl chloride with nitric acid in acetic anhydride gives an isomeric mixture containing about 33% ortho, 15% meta, and 52% para isomers (27) with benzal chloride, a mixture containing 23% ortho, 34% meta, and 43% para nitrobenzal chlorides is obtained. 

In an attempt to protect thiophenols during electrophilic substitution reactions on the aromatic ring, the three substituted thioethers were prepared. After acetylation of the aromatic ring (with moderate yields), the protective group was converted to the disulfide in moderate yields, 50-60%, by oxidation with hydrogen peroxide/boiling mineral acid, nitric acid, or acidic potassium permanganate. ... 

Aromatic rings can be nitrated by reaction with a mixture of concentrated nitric and sulfuric acids. The electrophile is the nitronium ion, N02+, which is generated from HNO3 by protonation and loss of water. The nitronium ion reacts with benzene to yield a carbocation intermediate, and loss of H+ from this intermediate gives the neutral substitution product, nitrobenzene (Figure 16.4). 

Nitroimidazoles substituted by an aromatic ring at the 2-position are also active as antitrichomonal agents. Reaction of p-fluorobenzonitrile (83) with saturated ethanolic hydrogen chloride affords imino-ether 84. Condensation of that intermediate with the dimethyl acetal from 2-aminoacetaldehyde gives the imidazole 85. Nitration of that heterocycle with nitric acid in acetic anhydride gives 86. Alkylation with ethylene chlorohydrin, presumably under neutral conditions, completes the synthesis of the anti-... 

This system was studied by Schwartz. Toluene at 10 ppm, nitric oxide at 1 ppm, and nitrogen dioxide at 1.2 ppm were irradiated with ultraviolet lamps in a 17-m batch reactor for 270 min. Collected aerosols were successively extracted with methylene chloride and then methanol. The methylene chloride extract was fractionated into water-soluble and water-insoluble material, and the latter fraction was further divided into acidic, neutral, and basic fractions. The acidic and neutral fractions were analyzed by gas chromatography and chemical-ionization mass spectrometry the compounds identified are shown in Figure 3-7. The two analyzed fractions represented only about 5.5% of the total aerosol mass. It is noteworthy that classical nitration of an aromatic ring appears to... 

For nitration of aromatic hydrocarbons with acetylnitrate, there is a clear linear correlation between the IPs of these hydrocarbons and rate constants relative to benzene (Pedersen et al. 1973). Table 4.4 jnxtaposes spin densities of cation-radicals and partial rate factors of ring attacks in the case of nitration of isomeric xylenes with nitric acid in acetic anhydride. 

Organic nitro compounds, RNO2, can be reduced to amines. The R may be either alkyl or aryl. Aromatic nitro compounds are easy to prepare and reduce. Their preparation utilizes a mixture of nitric acid and sulfuric acid to nitrate the aromatic ring. (However, multiple nitrations may occur, potentially causing problems.) The nitro group can be reduced with a... 

These compounds are less common than indole (benzo[ ]pyrrole). In the case of benzo[i>]furan the aromaticity of the heterocycle is weaker than in indole, and this ring is easily cleaved by reduction or oxidation. Electrophilic reagents tend to react with benzo[Z ]furan at C-2 in preference to C-3 (Scheme 7.21), reflecting the reduced ability of the heteroatom to stabilize the intermediate for 3-substitution. Attack in the heterocycle is often accompanied by substitution in the benzenoid ring. Nitration with nitric acid in acetic acid gives mainly 2-nitrobenzo[Z ]furan, plus the 4-, 6- and 7-isomers. When the reagent is in benzene maintained at 10 °C, both 3- and 2-nitro[ ]furans are formed in the ratio 4 1. Under Vilsmeier reaction conditions (see Section 6.1.2), benzo[Z ]furan gives 2-formylbenzo[6]furan in ca. 40% yield. 

Nitration of the aromatic ring of (223) occurs at the 7-position. However, its reaction with fuming nitric acid in acetic anhydride followed by treatment with methanol gave the 5-methoxy-4-nitro derivative. This product, on treatment with triethylamine, eliminated nitrous acid from the 3,4-positions. 

Some nitramines may be prepared without treating amines with nitric acid. The classical example is the so-called E-method of cyclonite preparation in which a nitramine is formed by dehydration of a mixture of paraformaldehyde and ammonium nitrate, i.e. without using either amine or nitric acid (this will be discussed more fully on p. 109). When a nitramine is required with a non-nitrated aromatic ring which readily undergoes nitration with nitric acid, Bamberger s method [45], involving the oxidation of diazo compounds (13), may be applied. 

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