What are electrophilic aromatic substitution reactions? How will you prepare
nitrobenzene from benzene?
Answers
Explanation:
Of course, there must be some boundary as to whether or not nitrobenzene undergoes a particular electrophilic aromatic substitution (EAS) since nitro-group is very deactivating. I leave it to you to decide that fact on the yield obtained in following reactions, because there are some data you may fail to find but, nonetheless, exist in literature.
Chlorination of nitrobenzene at 35 −45∘C in the presence of iron (III) chloride (FeCl3) gives an isomer mixture, which contains 86% 3-chloronitrobenzene, 10% 2-chloronitrobenzene and 4% 4-chloronitrobenzene (Ref.1). Even if nitro group is m-directing, this reaction has given significant amount of o-prodouct. You may compare this reaction with nitration reaction of chlorobenzene at 40 −70∘C with mixed acids (30% HNO3 : 56% H2SO4 : 14% H2O), which typically gives a 98% yield of an isomer mixture consisting of 34-36% 2-chloronitrobenzene, 63-65% 4-chloronitrobenzene, and about 1% 3-chloronitrobenzene (Ref.1).
A simple and efficient method for the sulfonation of nitrobenzene using liquid SO3 as the sulfonating agent in a microreactor at 40 −110∘C was developed and conducted recently, and 88% yield of 3-nitrobenzenesulfonic acid (m-NBSA) has been obtained (Ref.2). The main by-product is bis(3-nitrophenyl)sulfone (BNPS) and proposed mechanism was depicted in the Figure attached.
On the other hand, the sulfonation of toluene has given o:m:p ratio of 21.2% : 2.1% : 76.7% in 77.8% H2SO4 (Ref.3). The o:m:p ratio has become 38.8% : 2.6% : 58.6% when solvent has changed to 84.3% H2SO4 (significant decrease of p-product in increasing acidity; Ref.3). Also, note that the sulfonation by sulfuric acid of nitrobenzene itself and of various aromatic compounds in nitrobenzene solution has been studied at a series of temperatures (Ref.4). Yet, no concomitant sulfonation of nitrobenzene in the presence of other activated substrates such as toluene and xylene has been reported.
Using NO2+PF6− as the nitrating reagent, Olah had studied nitration of nitrobenzene in two different solvents: He achieved o:m:p ratio of 7.1% : 91.5% : 7.4% in 96% H2SO4 and that of 10% : 88.5% : 1.5% in CH3NO2 (Ref.3).
For comparison, same nitrating agent (NO2+PF6−) has given o:m:p ratio of 68.2% : 2% : 29.8% in CH3NO2 when subjected to nitrate toluene (Ref.3).
To my knowledge, Friedel-Crafts reaction of nitrobenzene (alkylation or acylation) is yet to be known. I'd love to hear if somebody say otherwise.
please mark me brainliest.
