Nitration benzene ring

One of the characteristic properties of phenol is the ease with which it gives substitution products, this property being particularly well shown by the ready nitration, sulphonation and bromination which the benzene ring in the phenol molecule undergoes. 

For this purpose, the usual oxidising agent is nitric acid, which in these circum stances (i.e., in the absence of sulphuric acid) does not nitrate the benzene ring. Owing to the nitrous fumes formed by the reduction of the nitric acid, the experiment should be performed in a fume upboard. 

Since the original observations of Vorlander, it has been recognised that positively charged substituents directly attached to the benzene ring are dominantly m-directing. Vorlander examined the nitration... 

Nitration by electrophilic aiomatic substitution is not limited to benzene alone but IS a general reaction of compounds that contain a benzene ring It would be a good idea to write out the answer to the following problem to ensure that you understand the rela tionship of starting materials to products m aromatic nitration before continuing to the next section... 

In compounds with a fused benzene ring, electrophilic substitution on carbon usually occurs in the benzenoid ring in preference to the heterocyclic ring. Frequently the orientation of substitution in these compounds parallels that in naphthalene. Conditions are often similar to those used for benzene itself. The actual position attacked varies compare formulae (341)-(346) where the orientation is shown for nitration sulfonation is usually similar for reasons which are not well understood. 

In the section dealing with electrophilic attack at carbon some results on indazole homocyclic reactivity were presented nitration at position 5 (Section 4.04.2.1.4(ii)), sulfon-ation at position 7 (Section 4.04.2.1.4(iii)) and bromination at positions 5 and 7 (Section 4.04.2.1.4(v)). The orientation depends on the nature (cationic, neutral or anionic) of the indazole. Protonation, for instance, deactivates the heterocycle and directs the attack towards the fused benzene ring. A careful study of the nitration of indazoles at positions 2, 3, 5 or 7 has been published by Habraken (7UOC3084) who described the synthesis of several dinitroindazoles (5,7 5,6 3,5 3,6 3,4 3,7). The kinetics of the nitration of indazole to form the 5-nitro derivative have been determined (72JCS(P2)632). The rate profile at acidities below 90% sulfuric acid shows that the reaction involves the conjugate acid of indazole. 

However, other studies on the nitration of a series of 3-methyl- and 3-ethyl-1,2-benzisoxazoles have shown that a mixture of the 5-nitro and 5,7-dinitro derivatives is formed (77IJC(B)1058, 77IJC(B)1061). The effect of substituents in the benzene ring is also of interest. If the 5-position is blocked, e.g. by a chloro group or by alkyl groups, nitration then occurs at the 4-position. 3-Alkyl-7-chloro and 3,7-dialkyl derivatives result in the formation of the appropriate 5-nitro derivative. The isomeric 3-alkyl-6-chloro- and 3,6-dialkyl-1,2-benzisoxazoles yield a mixture of the 5-nitro and 5,7-dinitro compounds. Both H NMR measurements and alternate syntheses were used in establishing the structures of these substitution products. 

The isothiazole ring causes deactivation of phenyl substituents, particularly in 3-phenyl-isothiazoles. Nitration of arylisothiazoles, however, occurs only in the benzene ring, the pattern of substitution varying greatly with the position of the aryl group on the isothiazole... 

Being a hydrocarbon with a solubility parameter of 18.6MPa - it is dissolved by a number of hydrocarbons with similar solubility parameters, such as benzene and toluene. The presence of a benzene ring results in polystyrene having greater reactivity than polyethylene. Characteristic reactions of a phenyl group such as chlorination, hydrogenation, nitration and sulphonation can all be performed with... 

The relative ease of preparation of condensed thiazole derivatives is a consequence of facile thiazole ring closure, and therefore also benzothiazole amines with an amino group on the benzene ring (except for the weakly regioselective nitration of benzothiazoles) are very easily accessible and useful substrates for the Gould-Jacobs reaction. 

The reactivity of Ce, C7, Cg aromatics is mainly associated with the benzene ring. Aromatic compounds in general are liable for electrophilic substitution. Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents. Benzene could be alkylated, nitrated, or chlorinated to important chemicals that are precursors for many commercial products. 

The chemistry of pyrrole is similar to that of activated benzene rings. In general, however, the heterocycles are more reactive toward electrophiles than benzene rings are, and low temperatures are often necessary to control the reactions. Halogenation, nitration, sulfonation, and Friedel-Crafts acylation can all be accomplished. For example ... 

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... 

The Husemann and Erdmann identification reactions for morphine and codeine in the DAB 9 (German Pharmacopoeia) involve the formation of the red-colored ortho-quinone (8) via apomorphine (5) under the influence of nitric acid with the simultaneous nitration of the benzene ring [15]. 

When two nitro-groups are introduced into the benzene ring the chief product is m-dinitrobenzene, which conforms to the following general laws of substitution. For aromatic compounds there are three important typical reactions 1, halogenation 2, nitration, and 3, sulpho-... 

This section also includes nitrated monocyclic arenes with halogen atoms directly attached to the benzene ring. 

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