O- and p-Dinitrobenzene

A further interesting application of the diazo reaction is in the preparation of the otherwise difficultly accessible o- and p-dinitrobenzenes (Expt 6.78). The requisite nitroaniline is converted into the diazonium fluoroborate which is then decomposed in aqueous suspension in the presence of sodium nitrite with the aid of copper powder. 

When treated with alkalis, o- and p- dinitrobenzenes are slowly converted to o- and p- nitrophenols, while with ammonia they form o- and p- nitroaniline. These reactions proceed slowly at room temperature, and more rapidly on heating. 

Pure o- and p- dinitrobenzenes may be obtained from the corresponding nitro-anilines in two ways either by diazotization (Meisenheimer and Patzig [34],) or by oxidation (Bamberger and Hiibner [35], Witt and Kopetschni [36]) ... 

Human poison by ingestion. Experimental poison by ingestion, intraperitoneal, and intravenous routes. Human systemic effects by skin contact cyanosis and motor activity changes. Experimental reproductive effects. An eye irritant. Mutation data reported. Mixture with nitric acid is a high explosive. Mixture with tetranitromethane is a high explosive very sensitive to sparks. When heated to decomposition it emits toxic fumes of NOx. See also o- and p-DINITROBENZENE. 

Aromatic diazonium salts on treatment with sodium nitrite decompose to form nitro compounds. This method represents a good procedure for obtaining o- and p-dinitrobenzenes, in 70% and 76% yield, respectively, from the corresponding diazonium sulfates. Improved yields in the preparation of dinitronaphthalenes are obtained when the decomposition of the diazonium sulfates is catalyzed by a cupro-cupri sulfite prepared by the interaction of copper sulfate and sodium nitrite. The procedure is illustrated by the synthesis of 1,4-dinitronaphthalene (60%). Occasionally, diazonium fluoborates are first formed, and these compounds are treated with sodium nitrite in the presence of copper powder, viz.,... 

High purity o- and p-dinitrobenzene can be obtained by the oxidation of o-and p-nitroaniline respectively. The oxidation was carried out with hydrogen peroxide (30%) in acetic acid [36]. 

Nitrations are usually carried out at comparatively low temperatures at higher temperatures there may be loss of material because of the oxidising action of the nitric acid. For substances which do not nitrate readily with a mixture of concentrated nitric and sulphuric acids ( mixed acid ), the intensity of the reaction may be increased inler alia by the use of fuming sulphuric acid (containing up to 60 per cent, of sulphur trioxide) or by fuming nitric acid. Thus nitrobenzene is converted by a mixture of fuming nitric acid and concentrated sulphuric acid into about 90 per cent, of wi-dinitrobenzene and small amounts of the o- and p-isomers the latter are eliminated in the process of recrystallisation ... 

As m- dinitrobenzene reacts with sodium sulphite with more difficulty, this reaction is now used for removing the o- and p- isomers from commercial dinitrobenzene (pp. 246-248). 

For a long time it was thought that a uniform substance was produced. However, m 1874 Rinne and Zincke [28], and also Komer [29] found that the o- and p- isomers are also formed along with large quantities of m- dinitrobenzene. 

Wyler [32] has carried out a vast amount of work on the nitration of benzene. He found that in the nitration of benzene or nitrobenzene on an industrial scale, a product was obtained containing up to 12% of the o- and p- isomers. This was contrary to the generally held opinion that dinitrobenzene contains only 1% of o- and 3% of p- dinitrobenzene. 

Wyler proved by a number of experiments with the nitration of nitrobenzene to dinitrobenzene, that the content of the o- and p- isomers in the product may vary from 5 to 15%, depending on the reaction conditions. At a low temperature, e.g. -17°C, equal amounts of the o- and p- isomers were formed, while higher temperatures favoured the formation of the o- isomer, this being on the whole in agreement with the earlier observations by Holleman and de Bruyn [31]. 

Trinitrobenzene may be obtained only in moderate yield by nitration of o- or p- dinitrobenzene. A product of high purity may be obtained from 2,4-di-nitroaniline (Komer and Contardi [56]) ... 

Among the six chlorodinitrobenzenes known, the 1,2,4- and 1,2,6-isomers are the most important as they are the principal products of the nitration of chlorobenzene. l-Chloro-2,4-dinitrobenzene results from the nitration of o- and p- chloronitrobenzenes and l-chloro-2,6-dinitrobenzene from the o- isomer. Apart from these, the 1,3,4-isomer, which forms in the nitration of m- chloronitrobenzene, is of some importance. 

Commercial l-chloro-2,4-dinitrobenzene prepared by the nitration of a mixture of o- and p- chloronitrobenzenes usually contains the 1,2,6-isomer. The latter differs from the 1,2,4-isomer in some of its properties. According to Borsche and Rants-cheff [24], only the 1,2,4-isomer can react with the sodium salt of acetylacetic ester, the 1,2,6-isomer remaining unchanged. 

There are cases, however, where the presence of the two isomers makes process control difficult, i.e. when the process is controlled by determining the melting point of the product. Then o- and p- chlorodinitrobenzenes are separated, and only the latter is nitrated, pure 1- chloro-2,4-dinitrobenzene being obtained. 

Nitrobenzene can be produced on a technical scale in yields up to 98 percent by nitration of benzene with mixed acid. The sulfuric acid serves as a solvent and generates the nitronium ion, which is the attacking electrophile [5]. Nitrobenzene itself may be further nitrated with a mixed acid giving m-dinitrobenzene. The o- and p-dini-trobenzenes are removed as water-soluble products by treating the nitration product with aqueous sodium sulfite, sodium 0- and p-nitrobenzenesulfonates being formed. The residual m-nitrobenzene is separated from the aqueous layer, washed with water and finally dried [11]. 

It should however be borne in mind that positions 9 and 10 in anthracene are not typically aromatic. They are manifested ]>y a higher reactivity than positions Ur and 0 as established by MO calculation [50]. In addition 9-nitroanthracene shows a non-planar structure with the nitro group out of plane [51] as pointed out by Cerfontain and Telder [48]. This is very similar to the position of the nitro group in o-dinitrobenzene and all derivatives of benzene with two ortho nitro groups. It is well known that the nitro groups in o-dinitrobenzene are not planar and there is no conjugation of double bonds in this compound. Tlie fact is also reflected in ultraviolet-absorption spectrum of o-dinitrobenzene which deviates from those of m- and p-dinitrobenzenes (Vol. I, p. 169, Table 20). 

Treatment of chlorobenzene with aqueous ammonia for 8 h at 300 °C generated aniline in 30% yield3. Phenol and diphenyl ether were the major side products. The uncatalyzed reactions of o- and p-chloronitrobenzene with ammonia occurred at 200 °C4. However, m-chloronitrobenzene did not react under these conditions, presumably due to the weaker stabilization of the charged intermediate. Interestingly, Wohl also found that in the presence of iodide ion, alcoholic ammonia reacts rapidly with o- and p-chloronitrobenzene at 100 °C5. 1-Chloro-2,4-dinitrobenzene reacted with alcoholic ammonia even at room temperature. 

The in-situ cell was then used by its inventors to investigate the reduction of nitrobenzene [4], o-, m-, and p-dinitrobenzenes [12] and substituted nitro-benzenes [13] in non-aqueous media. 

Dinitrobenzenes, C6H4(N02)2, are formed when benzene is heated with a mixture of nitric acid and sulphuric acid. The chief product of the reaction is m-dinitrobenzene, which crystallizes from alcohol in colorless needles, melts at 91°, and boils at 297°. o-Dinitrobenzene and p-dinitrobenzene, which melt at 118° and 172°, respectively, are also formed in small quantities. 

Excellent peak shape and baseline resolution of o-, m-, and p-dinitrobenzene were obtained on a silica column (2 = 254nm) using a 99.5/25/0.5 pentane/ dichloromethane/IPA mobile phase [628]. Detection limits of <10pg/mL and a linear concentration range up to 160ng/mL were reported. The analysis was complete in <10 min. 

Reduction of nitrobenzene and o, m and p-dinitrobenzene and dinitro-aniline in acid ammonia solutions. 

Yellow. Quinones, m- and p-nitroaniline, o-nitrophenol, and many other nitrO"Compounds. [Note that some nitro-compounds often appear yellow (e.g. m-dinitrobenzene and 3, 5 -dinitro-benzoic acid), but are colourless when absolutely pure.] Iodoform. 

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