Nitrating agent nitric acid

Direct nitration of pyrazoles, imidazoles, isoxazoles, and thiazoles has been carried out by Katritzky et al. with a new nitrating agent - nitric acid/trifluoroacetic anhydride [364, 365], This method allows obtaining mononitro derivatives of azoles in good yield (Table 5). 

THE NITRATION OF AROMATIC COMPOUNDS has been studied for decades, and benzene and its derivatives have been used almost exclusively as the substrates (I, 2). Nitric acid, usually in sulfuric acid, has generally been the nitrating reagent the nitronium ion, N02 +, has presumably been the specific nitrating agent. Nitric acid and the nitronium are both N(V) species. 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

Although the nitrating agent in nitration by nitric acid is less clear than when... 

The first attempts to esterify cellulose by means of nitric acid consisted in treating cellulose with the acid without any dehydrating agents. Vieille [1] discovered in 1882 that on nitration with nitric acid alone the rate of reaction and the nitrogen Content of the nitrocellulose increased as the concentration of HN03 was increased ... 

In 1924, Klemenc and Scholler [34] stated that m- xylene-2,6-disulphonic acid is nitrated with nitric anhydride in sulphuric acid twice as rapidly as when it is nitrated with nitric acid in sulphuric acid, the molar concentration being the same. This was illustrated in the following scheme, where the nitrating agent was denoted by X ... 

All this created doubt as to whether the nitronium ion mechanism can be applied to all cases. As will be pointed out later, it seems that the mechanism of the nitration reaction is more complicated and may proceed under the influence of nitrating agents other than the N02+ ion. According to Titov in his early work of 1941, nitration with nitric acid of moderate concentration (60-80% HN03) occurs through the action of N02 (or N204) and nitric acid plays only the role of a source of N02. 

Ceric Ammonium Nitrate (Cerium Ammonium Nitrate, Ammonium Hexanitratocerate). Ce(N03)4.2NH4N03, mw 548.3, small prismatic yeUow crysts, sol in w ale. Prepd by electrolytic oxidation of cerous nitrate in nitric acid soln, and subsequently mixing solns of cerium nitrate and AN, foUowed by crystn. It is a strong oxidizing agent and a dangerous fire risk in contact with organic materials... 

It is now generally accepted that the nitronium ion NOj is the main nitrat ing agent. Although most industrial nitrations are carried out by nitric acid -sulphuric acid mixtures, some compounds can be nitrated with nitric acid alone (production of tetryl, Vol. Ill, p. 42). Some products, such as PETN (Vol. II, p. 185) are usually obtained by nitration with nitric acid alone and Cyclonite (if made by nitration) is produced exclusively with nitric acid free of N2O4 (Vol. Ill, p. 87). 

Aniline also cannot be nitrated because nitric acid is an oxidizing agent and primary amines are easily oxidized. (Nitric acid and aniline can be an explosive combination.) Tertiary aromatic amines, however, can be nitrated. Because the tertiary amino group is a strong activator, nitration is carried out with nitric acid in acetic acid, a milder combination than nitric acid in sulfuric acid. About twice as much para isomer is formed as ortho isomer. 

Some recent observations on the intramolecular and intermolecular selectivity of some nitrating agents are presented in summary form in this paper. Attention will be concentrated on nitration by nitric acid in aqueous sulphuric acid, and by way of introduction reference will be made both to our own earlier studies and also to those of other workers in this field. It will become apparent that a situation of increasing complexity is being gradually revealed. 

Ingold and his co-workers( ) proposed and firmly established a scheme now generally accepted for the mechanism of aromatic nitration with nitric acid or mixed nitric and sulphuric acids as nitrating agents, typically, in homogeneous solution in an organic solvent. In this the nitronium ion, NO2, is the active intermediate which reacts with the aromatic compound, ArH -... 

Trifluoromethanesulfonic acid (triflic acid) is one of the strongest known Bronsted acids. Ho for CF3SOsH is -14.5, comparable to fluorosuifuric acid. Additionally, while fluorosuifuric acid, like sulfuric acid, is also a powerful sulfonating and oxidizing agent, trifluoromethanesulfonic add does not react with aromatics [6], It is therefore a most convenient strong acid for nitration with nitric acid, which is completely ionized by it. 

Today, silver nitrate AgNOj is used to cauterize wounds by converting nitrate to nitric acid. At the same time acting as a sterilizing agent and preventing infection with its anti-microbial properties. Silver is sometimes used to purify municipal water supplies. 

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