Figure 4-80. Intense light-induced addition of chlorine to benzene.
Hexachlorocyclohexane, the product of the chlorination reaction shown in Figure 4-80, was broadly used as an insecticide under the trade name Lindane, but not anymore. Lindane shampoo, however, is still available to treat scabies and lice. 4.5.5. Production and Applications of Benzene and Other Aromatic Hydrocarbons.
Modern methods to produce aromatic hydrocarbons are based on various thermal and catalytic processes in petrochemical refineries and coke plants. All these processes produce mixtures of aromatic compounds, which are separated by a variety of techniques. Simple aromatic compounds, including benzene, toluene, naphthalene, and isomers of xylenes as well as many of their derivatives are commercially available.
Aromatic compounds have an exceptionally broad spectrum of applications. Some of these applications have been around for a long time, such as in materials for construction, car, aircraft, and spacecraft building, manufacturing of dyes, fabrics, fibers, explosives, lubricants, coatings, adhesives, etc. Active ingredients of numerous pharmaceuticals and agrochemicals are aromatic derivatives, including Aspirin, Tylenol, Ibuprofen, and Naproxen. The second most widely used pesticide in the U.S.A. (after Glyphosate) is Atrazine, an aromatic compound.
The most modern application of aromatic compounds is in electronics. Without materials based on aromatic compounds, there would have been no LCD and OLED displays, no smartphones, no CDs and DVDs, no modern computers, no modern audio and video equipment. Quite amazingly, aromatic materials originally developed for a particular application, sometimes find use in a totally different area. For instance, Kevlar® (subsection 4.9.5 below), the aromatic polymer originally used to make bullet-proof vests, has more recently found use in top of the line loudspeakers made by the U.K. company Bowers & Wilkins (B&W) and preferred
by the renowned Abbey Road Studios in London, England. 4.5.6. Exercises.
1. Aromatic compounds are called aromatic because they all have a pleasant aroma. True or false? Answer
2. Benzene is (a) a liquid that boils below the boiling point of water and solidifies above the melting point of ice; (b) widely used in industry in spite of being toxic and carcinogenic; (c) a nonhazardous compound; (d) highly reactive toward Br2
that easily adds to all three C=C double bonds of benzene in the absence of a catalyst and light to give hexabromocyclohexane; (e) less reactive toward nitration and bromination than toluene. Answer
3. All six carbon-carbon bonds in benzene are equal in length and strength because the alternating double C=C bonds and single C-C bonds constituting the ring quickly interchange their positions. True or false? Answer
4. Draw chemical structures of (a) toluene; (b) naphthalene; (c) para
-dichlorobenzene; (d) 1,4-dinitrobenzene; (e) 1,3,5-tribromobenzene; (f) ortho
-difluorobenzene; (g) 1,2,3-trimethylbenzene; (h) para
5. What is wrong with the following chemical names: (a) 1,3,6-triethylbenzene; (b) 4,5-dinitrotoluene; (c) para
6. Using the hybridization concept, describe the electronic structure of benzene and explain the idea of π electron density delocalization. [Answer: See 4.5.2]
7. To prepare bromobenzene, C6
Br, from benzene C6
and bromine Br2
, the amount of bromine used per each mole of benzene should be (a) 0.5 mol; (b) 1 mol; (c) 2 mol. Answer
8. Write the mechanism of nitration of benzene with HNO3
in the presence of H2
9. Like benzene, benzoic acid is toxic and carcinogenic. True or false? Answer
10. Draw the structures of benzoic and terephthalic acids. [Answer: See Figures 4-77 and 4-78]
11. In industry, terephthalic acid is produced by oxidation of para
-xylene (1,4-dimethylbenzene) with KMnO4
. True or false? Answer
12. Define a Lewis acid, a Lewis base, a Brønsted-Lowry acid, and a Brønsted-Lowry base. Answer
13. Are toluene and xylenes homologues of benzene? Answer