Substitution reactions of benzene

REPRESENTATIVE ELECTROPHILIC AROMATIC SUBSTITUTION REACTIONS OF BENZENE... 

Representative Electrophilic Aromatic Substitution Reactions of Benzene... 

Repeat this analysis for the bromine addition and substitution reactions of benzene leading to trans-5,6-dibromo-l,3-cyclohexadiene and phenyl bromide, respectively. Do your thermochemical results account for the experimental observations ... 

For many years phenol was made on a large industrial scale from the substitution reaction of benzene sulfonic acid with sodium hydroxide. This produced sodium sulfite as a by-product. Production and disposal of this material, contaminated with aromatic compounds, on a large scale contributed to the poor economics of the process, which has now been replaced by the much more atom economic cumene route (see Chapter 2, Schemes 2.2 and 2.3). 

If we are correct in our assumption that the electrophilic substitution of aromatic species involves such a complexes as intermediates—and it has proved possible actually to isolate them in the course of some such substitutions (p. 136)—then what we commonly refer to as aromatic substitution really involves initial addition followed by subsequent elimination. How this basic theory is borne out in the common electrophilic substitution reactions of benzene will now be considered. 

Substitution reactions allow the aromatic sextet of tt electrons to be regenerated after attack by the electrophile has occurred. Electrophiles attack the tt system of benzene to form a delocalized nonaromatic carboca-tion (arenium ion or ct complex). Some specific examples of electrophilic substitution reactions of benzene are summarized below (see Chapter 5). 

Historically, the cyclic structure of benzene with symmetry, as shown in Fig. 7.3.15, was deduced by enumerating the derivatives formed in the mono-, di-, tri-substitution reactions of benzene. The structure can also be established directly using physical methods such as X-ray and neutron diffraction, NMR, and vibrational spectroscopy. We now discuss the infrared and Raman spectral data of benzene. 

Copy out this revision table about electrophilic aromatic substitution reactions of benzene and fill in the relevant electrophilic species and draw structures for the products... 

The readiness with which sulfonation takes place, however, varies considerably. Benzene and toluene can be sulfonated in the cold, whereas anthraquinone requires fuming sulfuric acid and high temperatures [10]. Unlike the other electrophilic substitution reactions of benzene, sulfonation is a readily reversible reaction. If water is not removed continuously during the reaction then the hydrolysis of sulfonic acid will lead to the inverse reaction to the starting product containing no sulfonate grouping. The overall process of sulfonation, if water is present in the reaction mixture, is represented by the following equation ... 

One of the commonest electrophilic substitution reactions of benzene is the simple nitration of the aromatic ring. In this reaction, the attacking electrophile is the nitronium ion, N02+, which may be... 

Give the mechanism of the electrophilic substitution reaction of benzene with an electrophile E+. 

On p. 475 we described how to observe the cationic intermediate in electrophilic substitution reactions of benzene by protonation in an NMR tube using a supetacid. In benzene the cation which forms is symmetrical. Doing the same experiment with toluene leads to protonation in the para position. 

Substitution Reactions of Benzene 479 Substitution Strongly Deactivating Substituents 503... 

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