Direct nitration

Aromatic hydrocarbons may be nitrated, i.e. the hydrogen atoms replaced by nitro (N02) groups, with concentrated nitric acid in the presence of concentrated sulphuric acid ( mixed acid reagent ). 

The function of the sulphuric acid is to convert the nitric add into the highly reactive, electrophilic, nitronium ion, N02, which is the effective nitrating agent. 

The mechanism of aromatic nitration, which is illustrated below in the case of benzene, is a two-step process involving electrophilic attack of the nitronium ion on the benzene molecule to form the intermediate mesomeric ion (1), followed by removal of a proton by the hydrogen sulphate ion, which is the most basic species in the reaction mixture. 

Nitration of aromatic hydrocarbons is usually carried out with the above mixed acid reagent at comparatively low temperatures (e.g. about 50 °C, as used in the preparation of nitrobenzene and 1-nitronaphthalene, Expt 6.17). Unnecessarily high temperatures should be avoided since polynitration is then more likely and oxidative breakdown of the aromatic ring system may occur. 

The deactivating effect of the nitro group is largely the result of its mesomeric interaction (-M effect) with the 7t-electron system of the benzene ring which is supplemented by the inductive (-/) effect (2). 

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Prepared by the direct nitration of naphthalene with a mixture of nitric and sulphuric acids. Its chief use was for the preparation of l-naphthyiamine and its derivatives. 

It is prepared by the direct nitration of toluene as a 50-60% component of the mixture of isomers. Used for the preparation of o-toluidine. 

It is prepared by the direct nitration of toluene with a mixture of nitric and sulphuric acids. TNT is a very stable, violent and powerful high explosive, but less sensitive to shock and friction than picric acid. It is widely used as a filling for shells, bombs, etc. often mixed with ammonium nitrate and other high explosives. The lower grades of TNT may contain isomers which under hot storage conditions may give rise to exudation. 

Since aliphatic hydrocarbons (unlike aromatic hydrocarbons, p. 155) can be directly nitrated only under very special conditions, indirect methods are usually employed for the preparation of compounds such as nitroethane, CjHsNO. When ethyl iodide is heated with silver nitrite, two isomeric compounds are formed, and can be easily separated by fractional distillation. The first is the true ester, ethyl nitrite, C,HiONO, of b.p. 17° its identity is shown by the action of hot sodium hydroxide solution, which hydrolyses it, giving ethanol and... 

The preparation of a number of miscellaneous acids is described. m-Nitrobenzoic acid. Although m-nitrobenzoic acid is the main product of the direct nitration of benzoic acid with potassium nitrate and concentrated sulphuric acid, the complete separation of the small quantity of the attendant para isomer is a laborious process. It is preferable to nitrate methyl benzoate and hydrolyse the resulting methyl w-nitrobenzoate, which is easily obtained in a pure condition ... 

Nitration in the 5-position of 4-methyl- and 2,4-dimethylselenazoles with HNO3-H2SO4 is more rapid than for thiazoles [4-methyl-5-nitroselenazole. m.p. 45°C (19) 2.4-dimethyl-5-nitroselenazole. m.p. 115-120 C (decomp.) (19)]. Direct nitration of 2-amino 4-methyl-selenazole leads to nng rupture (19). 

Direct nitration of aniline and other arylamines fails because oxidation leads to the formation of dark colored tars As a solution to this problem it is standaid practice to first protect the ammo group by acylation with either acetyl chloride or acetic anhydride... 

The net effect of the sequence protect-mtrate-deprotect is the same as if the substrate had been nitrated directly Because direct nitration is impossible however the indirect route IS the only practical method... 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

Nitration. Naphthalene is easily nitrated with mixed acids, eg, nitric and sulfuric, at moderate temperatures to give mostly 1-nitronaphthalene and small quantities, 3—5%, of 2-nitronaphthalene. 2-Nitronaphthalene [581-89-5] is not made in substantial amounts by direct nitration and must be produced by indirect methods, eg, the Bucherer reaction starting with 2-naphthalenol (2-naphthol [135-19-3]). However, the 2-naphthylamine [91-59-8] made using this route is a carcinogen thus the Bucherer method is seldom used in the United States. 

Dinitrotoluene can be prepared by the nitration of -nitrotoluene with yields of ca 96% or it can be obtained from the direct nitration of toluene. 

Nitration. Direct nitration of aromatic amines with nitric acid is not a satisfactory method, because the amino group is susceptible to oxidation. The amino group can be protected by acetylation, and the acetylamino derivative is then used in the nitration step. Nitration of acetanilide in sulfuric acid yields the 4-nitro compound that is hydroly2ed to -rutroaruline [100-01-6]. 

How much does Nitrogen Fertilizer Contribute to Nitrate Leaching when Winter Wheat is Growiii We saw earlier that direct nitrate losses from nitrogen fertilizer given to winter wheat are often relatively small. We saw too that... 

Nitromesitylene has been prepared by the direct nitration of mesitylene with concentrated nitric acid/ and by the action of benzoyl nitrate on mesitylene in carbon tetrachloride at low temperature. ... 

Nitrated fluoro compounds are synthesized by electrophilic (NOz+), radical (NO2 ), or nucleophilic (NO2-) methods Indirect nitration routes can suppress the side reactions associated with severe reaction conditions and some nitration reagents Novel fluoronitro compounds, unobtainable by direct nitration, can also be pre pared For example, the nitration of (2-fluoro-2,2-dinitroethoxy)acetaldoxime followed by oxidation of the nitroso intermediate with hydrogen peroxide yields 2-fluoro-2,2-dinitioethyl 2,2-dinitroethyl ether [f] (equation 1)... 

Substituted nitrobenzotrifluondes useful as intermediates for agrochemicals, pharmaceuticals, and liquid crystals are prepared by direct nitration of the respec-... 

The most notable chemistry of the biscylopen-tadienyls results from the aromaticity of the cyclopentadienyl rings. This is now far too extensively documented to be described in full but an outline of some of its manifestations is in Fig. 25.14. Ferrocene resists catalytic hydrogenation and does not undergo the typical reactions of conjugated dienes, such as the Diels-Alder reaction. Nor are direct nitration and halogenation possible because of oxidation to the ferricinium ion. However, Friedel-Crafts acylation as well as alkylation and metallation reactions, are readily effected. Indeed, electrophilic substitution of ferrocene occurs with such facility compared to, say, benzene (3 x 10 faster) that some explanation is called for. It has been suggested that. 

The direct nitration of 2-amino-4-methylselenazole leads to a ring fission. However, if the amino group is previously acetylated, the corresponding 5-nitro compound is formed in good yield 2-acetamido-4-methyl-5-nitroselenazole, mp 185°C. ... 

Although direct nitration was not possible, 2-amino-4-methylselena-zole can be directly brominated by treatment with bromine in carbon tetrachloride, the hydrogen bromide salt of 2-amino-4-methyl-5-bromoselenazole, mp 180°C (decomp.) is formed. However, all attempts to obtain the free base from this salt failed and led to complete decomposition. In this bromination, an equivalent quantity of bromine must be used excess also leads to complete destruction of the molecule. From the decomposition products an oily compound can be detected similar to bromoacetone. ... 

Nitrobenzene is an oily liquid, resulting from the direct nitration of benzene, having the following constitution —... 

Although the substitution of a preformed phthalocyanine always leads to a complex mixture of more- or less-substituted products, the reaction is of major industrial importance. Besides the chloro- and bromocopper phthalocyanines, also polysulfonated phthalocyanines, which are used as water-soluble dyes, are produced by the reaction of copper phthalocyanine with the respective reactant. While typical aromatic reactions of the Friedel-Crafts type are also possible,333 direct nitration of the macrocycle commonly results in oxidation of the phthalocyanine. However, under mild conditions it is possible to introduce the nitro group directly into several phthalocyanines.334... 

Where direct nitration results in degradation, a primary amine can be acylated, nitrated directly to form a secondary niiramine, which is then hydrolyzed to form the primary nitramine as exemplified in the following reaction sequence ... 

Tetryl. In the manufacture of Tetryl, it is usual not to nitrate dime thy laniline directly, but to dissolve it first in coned sulfuric acid and then to nitrate the dimethylaniline sulfate so obtained. Direct nitration of dimethylaniline proceeds so violently that it can be carried out only under specialized conditions. Many years experience of Tetryl manufacture has shown that the ratio of sulfuric acid to dimethylaniline should not be lower than 3 1, since a smaller amount of sulfuric acid may be detrimental to the nitration process. However, the ratio of sulfuric acid to dimethylaniline must not be too high, otherwise Tetryl yield is decreased. Temp must be maintained between 20-45° to avoid sulfonation of the benzene ring. Care must be exercised not to leave any unreacted dimethylaniline prior to introduction of nitric acid, because of the potential violence of the dimethyl-aniline-nitric acid reaction. Consequently, continuous methods of prepn are to be preferred as they inherently minimize accumulation of unreacted dimethylaniline... 

Another extremely important application area for FNA and RFNA is to either directly nitrate or be used in mixed acids to nitrate raw materials to yield widely used expls and proplnt ingredients (Refs 29,31,33,38 39). Also see under Nitration in this Vol Analytical. Analysis and assay procedures for nitric acid may be found in Refs 1, 2,10,11,15, 17, 27, 29, 34, 35, and in this Vol under Nitrogen Determinations in Energetic Materials. 

Mononitrophenols. OjN.CgH4.OH,mw 139.11, N 10.07%, OB to C02 —133.17%. Three isomers are possible but only two (o- and p-) are obtained by direct nitration. The nitration of phenol is much easier than that of aromatic hydrocarbons such as benz or toluene... 

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