Nitration, of aromatic compounds

Nitration of organic compounds has long been a very active and rewarding area of research and is the subject of a large body of literature. Extensive and well documented reviews have been published by Ingold [1], Olah [2,3,6], Schofield 

Institute) de Tecnologia Qmmica, UPV, Av. Naranjos s/n, E-46022 Valencia, Spain 

3 Nitration of aromatic compounds using zeolites as catalysts. 107 

The conventional nitration process,[2,5] that involves a mixture of nitric and sulfuric acids (mixed acids method) has remained unchallenged, in the commercial area, for the last 150 years owing to the very favourable economics. However, the method is notoriously unselective for nitration of substituted aromatic compounds and the disposal of waste products and spent acids is a serious environmental issue. For instance, nitration of toluene for production of mononitrotoluenes (MNTs) is conducted using a nitrating mixture usually composed of 52-56 % (w/w) H2SO4, 28-32% (w/w) HNO3 and 12-20% (w/w) H20. The reaction performed at temperatures between 25 and 40°C, yields ca. 96 % MNTs, which are composed of a mixture of ca. 60 % (w/w) o-nitrotoluene, ca. 37 % (w/w) p-nitrotoluene and 

Catalysts for Fine Chemical Synthesis, Vol. 4, Microporous and Mesoporous Solid Catalysts Edited by E. Derouane 2006 John Wiley Sons, Ltd 

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During my Cleveland years, I also continued and extended my studies in nitration, which I started in the early 1950s in Hungary. Conventional nitration of aromatic compounds uses mixed acid (mixture of nitric acid and sulfuric acid). The water formed in the reaetion dilutes the acid, and spent aeid disposal is beeoming a serious environ-... 

A simple kinetic order for the nitration of aromatic compounds was first established by Martinsen for nitration in sulphuric acid (Martin-sen also first observed the occurrence of a maximum in the rate of nitration, occurrii for nitration in sulphuric acid of 89-90 % concentration). The rate of nitration of nitrobenzene was found to obey a second-order rate law, first order in the concentration of the aromatic and of nitric acid. The same law certainly holds (and in many cases was explicitly demonstrated) for the compounds listed in table 2.3. 

TABLE 4.1 Nitration of aromatic compounds relative rates at 25 °C... 

TABLE 4.2 Nitration of aromatic compounds isomer proportions and partial rate factors ... 

The authors of this work were concerned chiefly with additions to alkenes, and evidence about the mechanism of aromatic nitration arises by analogy. Certain aspects of their work have been repeated to investigate whether the nitration of aromatic compounds shows the same phenomena ( 5-3-6). It was shown that solutions of acetyl nitrate in acetic anhydride were more powerful nitrating media for anisole and biphenyl than the corresponding solutions of nitric acid in which acetyl nitrate had not been formed furthermore, it appeared that the formation of acetyl nitrate was faster when 95-98% nitric acid was used than when 70 % nitric acid was used. 

Nitrations can be performed in homogeneous media, using tetramethylene sulfone or nitromethane (nitroethane) as solvent. A large variety of aromatic compounds have been nitrated with nitronium salts in excellent yields in nonaqueous media. Sensitive compounds, otherwise easily hydroly2ed or oxidized by nitric acid, can be nitrated without secondary effects. Nitration of aromatic compounds is considered an irreversible reaction. However, the reversibihty of the reaction has been demonstrated in some cases, eg, 9-nitroanthracene, as well as pentamethylnitrobenzene transnitrate benzene, toluene, and mesitylene in the presence of superacids (158) (see Nitration). 

Because of Us high polarity and low nucleophilicity, a trifluoroacetic acid medium is usually used for the investigation of such carbocationic processes as solvolysis, protonation of alkenes, skeletal rearrangements, and hydride shifts [22-24] It also has been used for several synthetically useful reachons, such as electrophilic aromatic substitution [25], reductions [26, 27], and oxidations [28] Trifluoroacetic acid is a good medium for the nitration of aromatic compounds Nitration of benzene or toluene with sodium nitrate in trifluoroacetic acid is almost quantitative after 4 h at room temperature [25] Under these conditions, toluene gives the usual mixture of mononitrotoluenes in an o m p ratio of 61 6 2 6 35 8 A trifluoroacetic acid medium can be used for the reduction of acids, ketones, and alcohols with sodium borohydnde [26] or triethylsilane [27] Diary Iketones are smoothly reduced by sodium borohydnde in trifluoroacetic acid to diarylmethanes (equation 13)... 

Tnflic acid is an excellent catalyst for the nitration of aromatic compounds [.S7]. In a mixture with nitnc acid, it forms the highly electrophilic nitronium inflate, which can be isolated as a white crystalline solid Nitronium inflate is a powerful nitrating reagent in inert organie solvents and in tnflic acid or sulfuric acid. It nitrates benzene, toluene, chlorobenzene, nitrobenzene, m-xylene, and benzotn-fluoride quantitatively in the temperature range of-110 to 30 °C with exeeptionally high positional selectivity [87],... 

Ozone-Mediated Nitration of Aromatic Compounds with Lower Oxides of Nitrogen," Mori, T. Srnm Synlett, 1995, 383... 

These are readily produced by nitration of aromatic compounds and are important explosives. The amines formed by reduction are able to undergo a nnmber of reactions, and have a wide range of application in the production of agrochemicals, dyestnffs, and pharmaceuticals. 

Nitration of aromatic compounds published in recent years is summarized in Table 2.1. 

Samajdar et al. (2000) performed nitration of aromatic compounds by bismnth nitrate on catalysis with montmorillonite KSF. The reaction develops in THF suspension on steering dnring 10 min. Nitration of anisole proceeds strictly in the para position (91% yield after 10 min), bnt in case of phenol, the reaction occnrs to be nonregioselective and 3 1 mixture of para and ortho nitro prod-nets is formed with a common yield of 89%. Nitration of estrone (the steroid phenol) also leads to 1 1 mixtnre of para and ortho nitrophenolic steroids in 94% yield. 

L. L. Kuznetsov u. B. V. Gidaspov, Nitration of Aromatic Compounds, Leningrad 1977. 

His work on nitration reactions did much to elucidate the mechanism of these reactions, particularly the nitration of aromatic compounds. He became a fellow of the Royal Society in 1924 was knighted in 1958. He was the recipient of many scientific honors medals Refs.-1) World Who s Who in Science, (A G. Debus, Ed), Marquis, Chicago (1968) 2) C ... 

WOLFFENSTEIN-BOTERS REACTION. Simultaneous oxidation and nitration of aromatic compounds to nitrophcnols with nitric acid or the higher oxides of nitrogen in the presence of a mercury salt as catalyst. Hydroxynitration of benzene yields picric acid. 

In contrast, direct nitration of aromatic compounds such as benzene takes place readily in the liquid phase, as discussed in Section 22-4C. 

The reported improvement in yields and selectivities in both mono- and poly-nitration of aromatic compounds using Claycop with acetic anhydride (and if necessary nitric acid) in tetrachloromethane has been investigated.28 The reagent system is found to be modestly catalytic and regioselective in the mononitration of toluene but is neither catalytic nor regioselective in the nitration of 2-nitrotoluene. 

Gas-phase nitration of aromatic compounds with nitrogen dioxide or the nitrating mixture is a serious ecological problem. It proceeds simultaneously in the atmosphere and results in the formation of cancer-producing components in air (Wamek 1988). 

There are many methods for effecting the nitration of aromatic compounds. Reactive compounds, for example, phenol, will nitrate in dilute nitric acid, but usually more vigorous reaction conditions consisting of nitric acid (either concentrated or fuming) or nitrate salts in sulfuric acid are used. Solutions of nitric acid in other mineral acids, e.g., perchloric or phosphoric acid, have sometimes been used and can give nitro products in isomeric proportions different from those found in sulfuric acid solution. Nitric acid inorganic solvents, particularly acetic acid or acetic anhydride, has also been used frequently. In acetic anhydride acetyl nitrate rather than the nitronium ion is usually the reacting species. 

Nitrations of aromatic compounds represent one of the most important classes or organic reactions. However, although a lot of data has been collected in relation to simple substituted benzenes, and the reactions have been subjected to quantitative and theoretical studies, the nitration of phenyl heterocycles has been much less studied in a systematic way. This chapter has attempted to bring together as much information as possible on the topic through a manual search of Chemical Abstracts and recent literature. 

NITRATION OF AROMATIC COMPOUNDS USING ZEOLITES AS CATALYSTS... 

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