Aromatic substitution reactions nitration

Other typical electrophilic aromatic substitution reactions—nitration (second entry) sul fonation (fourth entry) and Friedel-Crafts alkylation and acylation (fifth and sixth entnes)—take place readily and are synthetically useful Phenols also undergo elec trophilic substitution reactions that are limited to only the most active aromatic com pounds these include mtrosation (third entry) and coupling with diazomum salts (sev enth entry)... 

Nitro groups are meta-directing. Both nitro groups of m-dinitrobenzene direct an incoming substituent to the same position in an electrophilic aromatic substitution reaction. Nitration of m-nitrobenzene yields 1,3,5-trinitrobenzene. 

There are several lines of evidence for formation of cr complexes as intermediates in electrophilic aromatic substitution. One particularly informative approach involves measurement of isotope effects on the rate of substitution. If removal of the proton at the site of substitution were concerted with introduction of the electrophile, a primary isotope effect would be observed in reactions in which electrophilic attack on the ring is rate-determining. This is not the case for nitration nor for several other types of aromatic substitution reactions. Nitration of aromatic substrates partially labeled by tritium shows no selectivity between protium- and tritium-substituted sites. Similarly, the rate of nitration of nitrobenzene is identical to that... 

The nitration reactions described in this experiment aU demonstrate one of the classic electrophilic aromatic substitution reactions. Nitration has been used extensively in organic synthesis since a nitro group on an aromatic ring may be readily reduced to an amino group. 

The hydroxyl group is a strongly activating, ortho- and para-directing substituent in electrophilic aromatic substitution reactions (Section 16.4). As a result, phenols are highly reactive substrates for electrophilic halogenation, nitration, sulfonation, and lTiedel-Crafts reactions. 

Unlike benzene, pyridine undergoes electrophilic aromatic substitution reactions with great difficulty. Halogenation can be carried out under drastic conditions, but nitration occurs in very low yield, and Friedel-Crafts reactions are not successful. Reactions usually give the 3-substituted product. 

The central C-C double bond of dibenz[, /]oxepin displays the properties of an activated aromatic system and undergoes substitution reactions. Nitration and acid-catalyzed dcutcration gives the dibenzo[i>,/]oxepins 1 with the respective substituent in position 10.161... 

The aromatic substitution reaction that has received by far the closest study is nitration and, as a result, it is the one that probably provides the most detailed mechanistic picture. Preparative nitration is most frequently carried out with a mixture of concentrated nitric and sulphuric acids, the so-called nitrating mixture. The classical explanation for the presence of the sulphuric acid is that it absorbs the water formed in the nitration proper... 

While at Leeds from 1924 to 1930, Ingold s laboratory focused on three main topics of research (1) the nature and mechanism of orienting effects of groups in aromatic substitution (mainly nitration) (2) the study of prototropic rearrangements (shifts of H+) and aniontropic rearrangements (shifts of anions) as the ionic mechanisms of tautomerism and (3) the effect of polar substituents on the velocity and orientation of addition reactions to unsaturated systems. One of Ingold s students at Leeds, John William Baker, wrote a widely read book on tautomerism. 16... 

Of the aromatic substitution reactions, the most widely employed is nitration [19-22]. 

The title system in acetonitrile forms a homogeneous solution. The generation of NO+ cation takes place. As already known, NO+ is a remarkable, diverse reagent, not only for nitrosation and nitration but also for oxidation. Kochi and co-workers recently christened a new general mechanism oxidative aromatic substitution to describe aromatic substitution reactions (Kochi 1990 Bosch Kochi 1994). The mechanism incorporates ground-state electron transfer prior to the substitution step (see also Skokov Wheeler 1999). 

Know the meaning of electrophilic aromatic substitution, halogenation, nitration, sulfonation, alkylation, acylation, Friedel-Crafts reaction. 

All of the electrophilic aromatic substitution reactions follow this same general mechanism. The only difference is the structure of the electrophile and how it is generated. Let s look at a specific example, the nitration of benzene. This reaction is accomplished by reacting benzene with nitric acid in the presence of sulfuric acid ... 

In their study of aromatic substitution reactions, Olah and his coworkers have based much of their mechanistic analysis on the reactivity-selectivity principle. It was observed that electrophilic substitution reactions conducted with powerful nitrating agents... 

A wide variety of reactions other than substitutions and hydrolyses have been performed in microemulsions. Examples include alkylations [29], Knoevenagel condensations [13], oxidations [30,31], reductions [32], formation and decomposition of Meisenheimer complexes [33], aromatic substitution reactions such as nitration and bromination [34-36], nitrosation [37] and lactone formation, i.e. esterification [38-40]. Microemulsions have also been used for photochemical and electrochemical reactions [41-45]. 

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