Nitrating agent acidic” mixture

More obscure reagents used for 0-nitration include mixtures of phosphoric and nitric acids, and anhydrous nitric acid in which phosphorous pentoxide has been dissolved. The latter mixture contains dissolved dinitrogen pentoxide and is a powerful nitrating agent. A mixture of anhydrous nitric acid containing catalytic amounts of boron trifluoride has been reported to lead to the rapid 0-nitration of alcohols. "... 

Ethanoic anhydride reacts with concentrated nitric acid to yield the rather unstable ethanoyl nitrate (acetyl nitrate), which is a useful nitrating agent. With mixtures of benzene and methylbenzene, ethanoyl nitrate produces a mixture of nitrobenzene and 2- and 4-nitromethyl benzenes. When nitrated separately, each compound reacts at the same overall rate, but when mixed together, 25 times more nitromethylbenzene is formed than nitrobenzene. 

In addition to the conventional mixed acids commonly used to produce DNT, a mixture of NO2 and H2SO4 (8), a mixture of NO2 and oxygen (9), and just HNO (10) can also be used. TerephthaUc acid and certain substituted aromatics are more amenable to nitrations using HNO, as compared to those using mixed acids. For compounds that are easily nitratable, acetic acid and acetic anhydride are sometimes added to nitric acid (qv). Acetyl nitrate, which is a nitrating agent, is produced as an intermediate as follows ... 

Nitration of 4-(2-thienyl)- (301) and 4-(3-thienyl)-pyrazoles (302) mainly occurs on the thiophene ring, but when acetyl nitrate is used as the nitration agent small quantities of products nitrated on the pyrazole ring are isolated (position of the nitro group uncertain) (80CS( 15)102). Pyrazol-l -ylpyridines (303) undergo electrophilic reactions (bromination, chlorination and nitration) preferentially in the pyrazole ring. Thus, the nitration of (303 R = R = = H) either with a mixture of nitric acid and sulfuric acid at 10-15 °C or with... 

The question of what other species can be the active electrophile in nitration arises in the case of nitration using solutions of nitric acid in acetic anhydride. The solutions are very potent nitrating mixtures and effect nitrations at higher rates than solutions of nitric acid in inert organic solvents. Acetyl nitrate is formed in such solutions, and mty be the actual nitrating agent. 

Nitration Hazards arise from the strong oxidizing nature of the nitrating agents used (e.g. mixture of nitric and sulphuric acids) and from the explosive characteristics of some end products Reactions and side reactions involving oxidation are highly exothermic and may occur rapidly Sensitive temperature control is essential to avoid run-away... 

One of the most extensively studied examples of electrophilic substitution is the nitration of benzene. A mixture of nitric acid and concentrated sulfuric acid converts benzene slowly into nitrobenzene. The actual nitrating agent is the electrophile NQ2+ (the nitronium ion, ONO ), a linear triatomic ion ... 

Nitration of ketones or enol ethers provides a useful method for the preparation of a-nitro ketones. Direct nitration of ketones with HN03 suffers from the formation of a variety of oxidative by-products. Alternatively, the conversion of ketones into their enolates, enol acetates, or enol ethers, followed by nitration with conventional nitrating agents such as acyl nitrates, gives a-nitro ketones (see Ref. 79, a 1980 review). The nitration of enol acetates of alkylated cyclohexanones with concentrated nitric acid in acetic anhydride at 15-22 °C leads to mixtures of cis- and rrans-substituted 2-nitrocyclohexanones in 75-92% yield. 4-Monoalkylated acetoxy-cyclohexanes give mainly m-compounds, and 3-monoalkylated ones yield fra/w-compounds (Eq. 2.40).80... 

It is generally accepted that nitric acid-acetic anhydride mixtures contain acetyl nitrate (Equation 4.4). Acetyl nitrate is a weak nitrating agent but in the presence of a strong acid, like nitric acid, it can ionize to nitronium and acetate ions. Protonated acetyl nitrate could also be an active nitrating agent under these conditions. 

Acetic anhydride-nitric acid mixtures are extensively used for chloride-catalyzed nitrations. Other nitrating agents have been used and involve similar sources of electropositive chlorine for intermediate chloramine formation. 4,10-Dinitro-4,10-diaza-2,6,8,12-tetraoxaisowurtzitane (TEX) (40), an insensitive high performance explosive (VOD 8665 m/s, d = 1.99 g/cm ), is synthesized by treating the dihydrochloride salt of the corresponding amine (39) with strong mixed acid. ... 

The energetic nitramide (60) has been prepared from the nitration of the tris-acetamide (59) with nitric acid and acetic anhydride or trifluoroacetic anhydride. Nitric acid-trifluoroacetic anhydride mixtures are powerful nitrating agents and well suited for amide and urea A-nitration. 

The nitronium ion, N02 , is the active nitrating agent in nitric acid-sulfuric acid mixtures. The nitration of methylbenzene (toluene) is a typical example of a nitration that proceeds well using nitric acid in a 1 2 mixture with sulfuric acid. The nitration product is a mixture of 2-, 3-, and 4-nitromethylbenzenes ... 

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