Question

Starting with benzene, toluene, or phenol as the only sources of aromatic rings, show how to synthesize the following. Assume in all syntheses that mixtures of ortho-para products can be separated into the desired isomer. (a) 1-Bromo-3-nitrobenzene (b) 1 -Bromo-4-nitrobenzene (c) \(2,4,6\)-Trinitrotoluene (TNT) (d) \(m\)-Chlorobenzoic acid (e) \(p\)-Chlorobenzoic acid (f) \(p\)-Dichlorobenzene (g) \(m\)-Nitrobenzenesulfonic acid

Short answer

Question: Synthesize the following compounds using benzene, toluene, or phenol as a starting material: (a) 1-Bromo-3-nitrobenzene (b) 1-Bromo-4-nitrobenzene (c) 2,4,6-Trinitrotoluene (TNT) (d) m-Chlorobenzoic acid (e) p-Chlorobenzoic acid (f) p-Dichlorobenzene (g) m-Nitrobenzenesulfonic acid

Step-by-step solution

Nitration of benzene

Start with benzene and perform nitration using nitric acid and sulfuric acid to form nitrobenzene.

Bromination of nitrobenzene

Next, react nitrobenzene with bromine in the presence of a FeBr_3 catalyst to add Br at the 3-position due to the meta-directing effect of the nitro group, thus obtaining 1-Bromo-3-nitrobenzene. (b) 1-Bromo-4-nitrobenzene

Bromination of benzene

Start with benzene and perform bromination using bromine in the presence of a FeBr_3 catalyst to form bromobenzene.

Nitration of bromobenzene

Next, react bromobenzene with nitric acid and sulfuric acid to add NO_2 at the 4-position due to the para-directing effect of the bromine, thus obtaining 1-Bromo-4-nitrobenzene. (c) 2,4,6-Trinitrotoluene (TNT)

Nitration of toluene

Start with toluene and perform nitration using a mixture of nitric acid and sulfuric acid to form 2-nitrotoluene and 4-nitrotoluene.

Dinitration of 2-nitrotoluene and 4-nitrotoluene

Perform nitration again on 2-nitrotoluene and 4-nitrotoluene, using more concentrated nitric acid and sulfuric acid, to form 2,4-dinitrotoluene and 2,6-dinitrotoluene.

Final nitration of 2,4-dinitrotoluene

Perform nitration one more time on 2,4-dinitrotoluene using highly concentrated nitric acid and sulfuric acid to form 2,4,6-trinitrotoluene (TNT). (d) m-Chlorobenzoic acid

Nitration of benzene

Start with benzene and perform nitration using nitric acid and sulfuric acid to form nitrobenzene.

Reduction of nitrobenzene to aniline

Reduce nitrobenzene to aniline using a reducing agent such as hydrogen over a metal catalyst like palladium or platinum.

Diazotization of aniline

Perform diazotization on aniline using nitrous acid (obtained from sodium nitrite and hydrochloric acid) to form benzenediazonium chloride.

Sandmeyer reaction to form m-chloronitrobenzene

Perform the Sandmeyer reaction on benzenediazonium chloride using cuprous chloride (CuCl) to form m-chloronitrobenzene.

Reduction of m-chloronitrobenzene

Reduce m-chloronitrobenzene using a reducing agent such as iron metal and hydrochloric acid to form m-chloroaniline.

Oxidation of m-chloroaniline

Oxidize m-chloroaniline using a strong oxidizing agent like potassium permanganate (KMnO_4) to form m-chlorobenzoic acid. (e) p-Chlorobenzoic acid

Chlorination of benzene

Start with benzene and perform chlorination using chlorine in the presence of a FeCl_3 catalyst to form chlorobenzene.

Nitration of chlorobenzene

React chlorobenzene with nitric acid and sulfuric acid to form p-nitrochlorobenzene due to the para-directing effect of the chloride.

Reduction of p-nitrochlorobenzene to p-chloroaniline

Reduce p-nitrochlorobenzene to p-chloroaniline using a reducing agent such as hydrogen over a metal catalyst like palladium or platinum.

Oxidation of p-chloroaniline

Oxidize p-chloroaniline using a strong oxidizing agent like potassium permanganate (KMnO_4) to form p-chlorobenzoic acid. (f) p-Dichlorobenzene

Chlorination of benzene

Start with benzene and perform chlorination using chlorine in the presence of a FeCl_3 catalyst to form chlorobenzene.

Chlorination of chlorobenzene

Perform chlorination again on chlorobenzene using chlorine in the presence of a FeCl_3 catalyst to form p-dichlorobenzene. (g) m-Nitrobenzenesulfonic acid

Nitration of benzene

Start with benzene and perform nitration using nitric acid and sulfuric acid to form nitrobenzene.

Sulfonation of nitrobenzene

Perform sulfonation on nitrobenzene using fuming sulfuric acid to form m-nitrobenzenesulfonic acid. The sulfonic acid group will add at the meta position due to the meta-directing effect of the nitro group.