Benzene derivatives nitration

The so-called Janovsky reaction [53] is a very characteristic one for many higher nitrated benzene derivatives. It is probably also of nucleophilic character. It consists in treating a diluted di- or tri-nitro compound solution in acetone with a concentrated solution of potassium or sodium hydroxide (generally of 30% concentration). The acetone solution turns bright coloured. Red to violet colours may appear according to the nitro compound present. 

It is characteristic that the new entrant methyl group assumes the ortho position to the nitro group and thus a substitution occurs which is similar to nucleophilic attack. Recently it has been found by Jackson and Waters [72] that higher nitrated benzene derivatives such as m- dinitrobenzene, or 1,3,5-trinitrobenzene, become homolytic hydrogen acceptors at temperatures of 80-100°C especially in the presence of the 2-cyano-2-propyl radical, which is formed by thermal decomposition of a,a -azo-bis-isobutyronitrile... 

It will be recalled that not only halogen atoms, but also nitro and sulfo groups, can be replaced by phenyl- or arylamines. The lability of the nitro group, particularly in the anthraquinone nucleus, permits the preparation of some important intermediates which cannot be discussed here. Also, highly nitrated benzene derivatives give access to interesting condensation products. 

The development of resistance to chlorinated and nitrated benzene derivatives has been studied by several researchers (Priest and Wood, 1961 Georgopoulos and Zaracovitis, 1967). Botrytis allii strains in cultures under laboratory conditions could be resistant to tetrachloronitrobenzenes, dicloran and 2,3,5,6-tetra-chloronitroaniline (Priest and Wood, 1961). Resistance was not important under field conditions (Kuiper, 1965 Skorda, 1977). 

In 1889, a turning point in perfume preparation had come, when Aime Guerlain introduced his perfume /icfcy , in which, for the first time, only synthetically generated vanillin, coumarin and heliotropin (3,4-methylenedioxy-benzaldehyde also known as piperonal) were used. In the course of his work on highly nitrated benzene derivatives, which would become very important as explosives, the French chemist Albert Baur found by chance a group of compounds with a musk odour. Ferdinand Tiemann in Berlin, looking for a syn-... 

Henna, resorcinol, thymol, silver nitrate, benzenic derivatives... 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

If, on the other hand, the encounter pair were an oriented structure, positional selectivity could be retained for a different reason and in a different quantitative sense. Thus, a monosubstituted benzene derivative in which the substituent was sufficiently powerfully activating would react with the electrophile to give three different encounter pairs two of these would more readily proceed to the substitution products than to the starting materials, whilst the third might more readily break up than go to products. In the limit the first two would be giving substitution at the encounter rate and, in the absence of steric effects, products in the statistical ratio whilst the third would not. If we consider particular cases, there is nothing in the rather inadequate data available to discourage the view that, for example, in the cases of toluene or phenol, which in sulphuric acid are nitrated at or near the encounter rate, the... 

TABLE 9.3 The nitration of benzene derivatives containing positively charged substituents ... 

The range of preparatively useful electrophilic substitution reactions is often limited by the acid sensitivity of the substrates. Whereas thiophene can be successfully sulfonated in 95% sulfuric acid at room temperature, such strongly acidic conditions cannot be used for the sulfonation of furan or pyrrole. Attempts to nitrate thiophene, furan or pyrrole under conditions used to nitrate benzene and its derivatives invariably result in failure. In the... 

When a mono-substituted benzene derivative, C6H5Y, undergoes further electrophilic substitution, e.g. nitration, the incoming substituent may be incorporated at the o-, m- or p-position, and the overall rate at which substitution takes place may be faster or slower than with benzene itself. What is found in practice is that substitution... 

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-... 

Maeda, N., Ohya, T., Nojima. K.. and Kanno. S. Formation of cyanide ion or cyanogen chloride through the cleavage of aromatic rings by nitrous acid or chlorine. IX. On the reactions of chlorinated, nitrated, carboxylated or methylated benzene derivatives with hypochlorous acid in the presence of aimnonium ion, Chemosphere, 16(10-12) 2249-2258, 1987. 

Feng et al. (1986) performed quantum-chemical calculations of aromatic nitration. The resnlts they obtained were in good accordance with the IPs of N02 and benzene and its derivatives. The radical-pair recombination mechanism is favored for nitration whenever the IP of an aromatic molecule is much less than that of N02. According to calculations, nitration of toluene and xylene with N02 most probably proceeds according to ion-radical mechanism. Nitration of nitrobenzene and benzene derivatives with electron-acceptor substituents can proceed through the classical polar mechanism only. As for benzene, both mechanisms (ion-radical and polar) are possible. Substituents that raise the IP of an aromatic molecule to a value higher than that of N02 prevent the formation of this radical pair (one-electron transfer appears to be forbidden). This forces the classical mechanism to take place. It shonld be nnderlined that a solvent plays the decisive role in nitration. 

Having in mind the mentioned importance of gas-phase aromatic nitration, it should be useful to arrange benzene derivatives as electron donor with respect to nitronium ion, using IPs. These potentials have been measured in the gaseous phase and can be extracted from NIST Chemistry WebBook (Lindstrom and Mallard, 2003). The data provide an indication for the thermodynamic feasibility of their one-electron oxidation by nitronium cation. 

Benzo[6 jthiophenes with nitro groups at the 4-, 5-, 6- or 7-positions may be synthesized by ring closure reactions of appropriately substituted benzene derivatives. Nitration of 5-acetaminobenzo[6]thiophene gives the 4-nitro derivative, which can be hydrolyzed and deaminated to yield 4-nitrobenzo[6]thiophene (equation 44). 5-Nitrobenzo[6]thiophene is conveniently available by decarboxylation of 5-nitrobenzo[6]thiophene-2-carboxylic acid, which in turn is available by a Perkin reaction of 4-nitro-2-formylphenylthioglycoIic ester (equation 45 Section 3.15.2.3). The 7-nitro isomer may be obtained similarly. 

Like other electrophilic substitutions, nitration of a substituted benzene, where the substituent is electron withdrawing (N02, C02H, CN, and so on Table 22-6), generally produces the 1,3-isomer. To prepare the 1,4-isomer, less direct routes are necessary— the usual strategem being to use benzene derivatives with substituent groups that produce the desired orientation on... 

Trinitro-3-chlorophenol or Chloropicric Acid, yel crysts(AcOH or ale) or prisms(from w), mp 112-19°, not volatile with steam mod sol in chlf, benz, ale or eth can be obtd as the ultimate product of nitration of all mono- di-nitro-3-chlorophenols (Refs 2 3). It forms yel salts of Na, Ag, NH3 (mp 223 24 °) PhNH2 (mp 189 90°). See Refs 2, 3, 5,6, 7 8 for other props methods of prepn. The Chloride salt, an expl compd called Chloropicryl Chloride, is mentioned under Trinitrochloro-benzenes, Derivatives of Chlorobenzene... 

In experiments of major importance, first published in 1950, Melander found that in the nitration and bromination of a number of benzene derivatives the tritium isotope effect (kHlkT) is not 10-20 as is to be expected if carbon-hydrogen bond breaking occurs in the rate-determining step, but rather is less than 1.3. The direct displacement mechanism was thus ruled out, and the two-step mechanism of Equation 7.70 with the first step rate-determining was implicated.157... 

Table 7.17 Relative Rates of Nitration of Benzene Derivatives ...

Table 7.18 Relative Rates of Aromatic Nitration of Benzene Derivatives with N02+BF4 and with CH30N02-BF3...

The production of anthraquinone dyes generally proceeds from a few key products generated by electrophilic substitution of unsubstituted anthraquinone or by synthesis of the nucleus. The major methods employed to prepare anthraquinone derivatives substituted in the a-position are sulfonation and nitration. Preparation of b-substituted anthraquinones and of quinizarin (1,4-dihydroxyan-thraquinone) generally is accomplished by synthesis of the nucleus starting from phthalic anhydride and a benzene derivative. 

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