Nitration, aromatic nitro compounds

Name Nitroglycerine and nitroglycol with collodion cotton Am- monium nitrate Sodium nitrate Aromatic nitro compounds Wood- meal Dye... 

Keywords aromatic compound nitric acid, acetic anhydride, zeolite, nitration, aromatic nitro compound... 

Nitration is important for two reasons firstly, because it is the most general process for the preparation of aromatic nitro compounds secondly, because of the part which it has played in the development of theoretical organic chemistry. It is of interest because of its own characteristics as an electrophilic substitution. 

Nitrobenzene was first synthesized in 1834 by treating benzene with fuming nitric acid (1), and was first produced commercially in England in 1856 (2). The relative ease of aromatic nitration has contributed significantly to the large and varied industrial appHcations of nitrobenzene, other aromatic nitro compounds, and their derivatives. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

The aromatic skeleton is nitrated in the first reaction step. Then titanium(Ill) chloride in acid medium is used to reduce the aromatic nitro compounds so produced to the corresponding amines, which in turn are diazotized and coupled to N-(l-naphthyl)-ethylenediamine to yield an azo dye (cf. Fig. 21). 

Aromatic nitro compounds are obtained by nitrating appropriately substituted benzene derivatives with nitric acid. This reagent can be employed in a more or less concentrated form and is often used in combination with concentrated sulfu-... 

The reduction of aromatic nitro-compounds is of exceptionally great interest, not only scientifically, hut also technically. The conversion of the hydrocarbons of coal tar into useful products began with the discovery of the nitration process the conversion, on the technical scale, of the nitro-group of nitrobenzene into the amino-group gave aniline, the starting material for the preparation of innumerable dyes and pharmaceutical products to aniline were added the homologous toluidines, xylidines, naphthylamines, and so on. 

The nitration of aromatic hydrocarbons is one of the most widely studied and well-documented reactions in organic chemistry. Aromatic nitro compounds are of huge industrial importance in the synthesis of pharmaceutical drugs, agrochemicals, polymers, solvents and perfumes, and for the synthesis of other industrially important chemicals containing amine and isocyanate functionality. However, early research into aromatic nitration was fuelled exclusively by their use as explosives and intermediates in the synthesis of dyestuffs. The former is the subject of this chapter. 

The direct nitration of aromatic substrates is usually the method of choice for the synthesis of aromatic nitro compounds on both industrial and laboratory scales. Other routes are usually only considered when the required product has an unusual substitution pattern or is so deactivated that nitration is exceptionally difficult. Many of these alternative methods are limited to a laboratory scale. 

Nitrations giving a complex mixture of products are not useful in organic chemistry or for the synthesis of explosives, and so, another route to the required product should be considered which is more selective. Although it is acceptable for commercial explosives to contain a mixture of aromatic nitro compounds, military explosives are almost always single compounds with well-defined physical properties. 

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... 

Smokeless propellants may be taken as another example of composite explosives. These may be either mixtures of nitrocellulose of differing degrees of nitration, partly in a colloidal and partly in a fibrous state with an admixture of the remaining solvent and a stabilizer or a solution of nitrocelluloses in carbamite (centralite) and nitroglycerine with an admixture of components such as aromatic nitro compounds, nitroguanidine, graphite etc. 

These mixtures found no practical application since picric acid gradually reacts with salts to form picrates with the evolution of free acid. The picrates so formed are highly sensitive to friction and impact, and the free acid acts corrosively. Mixtures with chlorates showed a particular sensitiveness to friction and impact, hence doubt was expressed as to their practical value. Nevertheless, the idea of completing the defective oxygen balance in aromatic nitro compounds by the addition of such oxidizing agents as nitrates was carried out in such a way as to produce mixtures useful for various practical purposes. 

Mixtures of aromatic nitro compounds with ammonium nitrate were widely used during World War I, when the enormous demand for high explosives could not be met by the output of TNT, trinitronaphthalene, picric acid, trinitroanisole, trinitrophenetole, dinitrobenzene, hexyl etc. 

The explosive properties of mixtures with ammonium nitrate depend on the quantitative relationship between the oxidizing agent and the explosive or combustible substance. According to Parisot and Laffitte s [9, 47] investigations the explosive properties of mixtures of aromatic nitro compounds with ammonium nitrate vary with the change in composition of the system in an almost rectilinear manner. The graph in Fig. 69 shows how the rate of detonation depends on the composition of mixtures of tetryl or picric acid with ammonium nitrate. T. Urbanski et al. [48] also obtained a rectilinear relationship for nitrostarch mixtures with ammonium or sodium nitrate (Fig. 71, p. 265). 

Name Ammo- nium nitrate Sodium nitrate Potassium perchlorate Nitroglycerine and nitroglycol Nitro- cellulose Aromatic nitro compounds Wood- meal Various... 

As early as 1929 Plyler and Steele [10] began an investigation of the infra-red spectra of nitric esters in the range methyl to n-butyl nitrates. Dadieu, Jele and Kohlrausch [11] studied the Raman spectra of nitric esters as well as inorganic nitrates, and aliphatic and aromatic nitro compounds. 

Many compounds have been tested as ignition quality improvers—additives which shorten the ignition delay to a desirable duration. An extensive review in 1944 (6, 43) listed 303 references, 92 dealing with alkyl nitrates and nitrites 61 with aldehydes, ketones, esters, and ethers 49 with peroxides 42 with aromatic nitro compounds 29, with metal derivatives 28 with oxidation and oxidation products 22 with polysulfides 16 with aromatic hydrocarbons nine with nitration and four with oximes and nitroso compounds. In 1950, tests at the U. S. Naval Engineering Experiment Station (48) showed that a concentration of 1.5% of certain peroxides, alkyl nitrates, nitroaikanes, and nitrocarbamates increased cetane number 20 or more units. 

Of the hydrocarbons toluene is the only one which nitrates sufficiently easily and yields a product which has the proper physical and explosive properties. Trinitrotoluene is the most widely used of the pure aromatic nitro compounds. It melts at such temperature that it can be loaded by pouring. It is easily and surely detonated, and is insensitive to shock, though not insensitive enough to penetrate armor-plate without exploding until afterwards. It is powerful and brisant, but less so than trinitrobenzene which would offer certain advantages if it could be procured in sufficient quantity. 

Pentryl, or 2,4,6-trinitrophenyInitraminoethyI nitrate, is another explosive which is derived from ethylene. It is a nitric ester, an aromatic nitro compound, and a nitroamine. The substance was described in 1925 by Moran54 who prepared it by the action of mixed acid on 2,4-dinitrophenylethanolamine (large orange-yellow crystals from alcohol, m.p. 92°) procured by the interaction of dinitrochlorobenzene with ethanolamine. von Herz later prepared pentryl by the nitration of 0-hydroxyethylaniline, a material which is more commonly called phenylethanolamine and is now available commercially in this country, and was granted... 

The sensitiveness of ammonium nitrate to initiation is increased by the addition to it of explosive substances, such as nitroglycerin, nitrocellulose, or aromatic nitro compounds, or of... 

Many polycyclic aromatic amines and aldehydes are commercially available, but their supply is very limited. Preparation of these starting materials is necessary for studying the (3-lactam formation reaction [93]. Nitro compounds are the precursors for the amines. An important task was to prepare polycyclic aromatic nitro compounds, particularly those of chrysene, phenanthrene, pyrene, and dibenzofluorene in good yield. Nitration of these hydrocarbons with concentrated nitric acid in sulfuric acid is a widely used reaction for this purpose. Our research culminated in facile synthesis of polyaromatic nitro derivative 9 starting from polyaromatic hydrocarbons (PAHs) 8 through the use of bismuth nitrate impregnated with clay (Scheme 1) ([94, 95] for some examples of bismuth nitrate-catalyzed reactions... 

Nitro compounds and their reduction products. Tertiary aliphatic nitro compounds and aromatic nitro compounds are reduced by zinc and ammonium chloride solution to the corresponding hydroxylamines, which may be detected by their reducing action upon an ammoniacal solution of silver nitrate or Tollen s reagent ... 

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