M- Chloronitrobenzene

An ortho nitro group exerts a comparable rate enhancing effect m Chloronitrobenzene although much more reactive than chlorobenzene itself is thousands of times less reac tive than either o or p chloronitrobenzene... 

Nucleophilic aromatic substitution occurs only if the aromatic ring has an electron-withdrawing substituent in a position ortho or para to the leaving group. The more such substituents there are, the faster the reaction. As shown in Figure 16.18, only ortho and para electron-withdrawing substituents stabilize the anion intermediate through resonance a meta substituent offers no such resonance stabilization. Thus, p-ch oronitrobenzene and o-chloronitrobenzene react with hydroxide ion at 130 °C to yield substitution products, but m-chloronitrobenzene is inert to OH-. 

TRINITROBENZENE m-DIBROMOBENZENE m-CHLORONITROBENZENE o-CHLORONITROBENZENE p-CHLORONITROBENZENE tn-D I CHLOROBENZENE o-DICHLOROBENZENE p-DI CHLOROBENZENE m-DIFLUOROBENZENE o-DIFLUOROBENZENE p-DIFLUOROBENZENE m-DI NITROBENZENE o-DINITROBENZENE p-DINITROBENZENE BROMOBENZENE MONOCHLOROBENZENE m-CHLOROPHENOL o-CHLOROPHENOL p-CHLOROPHENOL... 

A different mode of reaction, however, is observed in photoreductions of nitroaromatics by aromatic tertiary amines. Irradiation of benzene solutions of N-methylated anilines and either m-chloronitrobenzene or 1-nitronaphthalene results in oxidative demethylation of the amines accompanied with reduction of the nitro compound to the corresponding arylamine 49). The authors suggest that hydrogen abstraction from the methyl group takes place as the primary chemical event. 

Problem 11.17 Indicate by an arrow the position(s) most likely to undergo electrophilic substitution in each of the following compounds. List the number of the above rule(s) used in making your prediction, (a) m-xylene, (6) p-nitrotoluene, (c) m-chloronitrobenzene, (d) p-methoxytoluene, (e) p-chlorotoluene, (/) m-nilrotoluene, (g) o-methylphenol (o-cresol). 

In an exactly analogous manner there is obtained from 30 gms. of m-nitroamlinc, 23 gms. (87%) of 3 3 -dinitrodiphenyl (yellow needles insoluble in cold glacial acetic acid M.P. 200°) and 6 gms. (20%) of m-chloronitrobenzene (colourless crystals insoluble in cold benzene M.P. 45° if rapidly cooled after fusion, melts at 24°, but in a short time reverts to the stable modification). (O. S., IX., 92.)... 

Details of the preparation of p-chlorotoluene are given in Expt 6.71, which also includes o-chlorotoluene, chlorobenzene, m-chloronitrobenzene and o-chlorobenzoic acid as examples of cognate preparations. 

Chlorination of nitrobenzene would not be a suitable route to the required intermediate, because it would produce mainly m-chloronitrobenzene. 

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