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Benzene is a colorless, sweet-smelling hydrocarbon with molecular formula C6H6. The sweet odor of benzene is familiar to anyone who has visited a gas station: the compound is a byproduct of the fuel-refining process. Benzene is an aromatic compound, meaning it’s extremely stable. Although benzene occurs naturally it is extensively used in a variety of industrial processes. This ubiquity comes at a cost, though: benzene is a known carcinogen. Take a deep—not too deep!—sniff; it’s time to learn about benzene.
By analyzing questions, you can see patterns emerge, patterns that will help you answer questions. Qwiz5 is all about those patterns. In each installment of Qwiz5, we take an answer line and look at its five most common clues. Here we explore five clues that will help you answer a tossup on benzene.
AUGUST KEKULÉ
German chemist August Kekulé was the first to propose a workable hypothesis for the structure of benzene. Although benzene had been distilled from coal tar since at least 1845, prior to Kekulé no one had been able to explain its unique properties. Kekulé proposed that benzene was a hexagonal ring of carbon atoms with alternating double and single bonds. According to the chemist, the epiphany of the molecule’s structure came to him in a dream.
BIRCH REDUCTION
The Birch Reduction is a reduction reaction that removes one of benzene’s double bonds. In a Birch Reduction benzene is reacted with metallic sodium or lithium in a liquid ammonia solvent with alcohol. The Birch Reduction is useful because it is a selective reaction—it only reduces one of benzene’s double bonds to form a compound called 1,4-cyclohexadiene. This allows us to create many interesting compounds with a variety of medical applications, including the eventual development of steroid hormones.
PHENOL
Phenol is a common derivative of benzene. Also known as carbolic acid, phenol consists of benzene with a hydroxyl group (chemical formula –OH) bonded to one of the carbons of the benzene ring. Phenol has numerous industrial applications, ranging from pharmaceuticals to nylons.
TOLUENE
Toluene is another common benzene derivative. Like phenol it is a monosubstituted benzene. This means that one of the carbons on the benzene ring is bonded to a methyl group (chemical formula –CH3) instead of a hydrogen atom. Toluene is commonly used as a solvent and can be found in certain glues or paint thinners.
FRIEDEL-CRAFTS REACTION
Friedel-Crafts reactions occur in two variants: Friedel-Crafts acylation and Friedel-Crafts alkylation. In a Friedel-Crafts acylation benzene interacts with an acetyl chloride in the presence of an aluminum trichloride catalyst. The resulting compound is a benzene with an acetyl group attached. Alkylation is very similar: an alkyl-chloride interacts with benzene in the presence of an aluminum trichloride catalyst. The product of this reaction is benzene with an attached alkyl group. These compounds have numerous industrial applications.
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Quizbowl is about learning, not rote memorization, so we encourage you to use this as a springboard for further reading rather than as an endpoint. Here are a few things to check out:
Visit this site to learn more about benzene’s many derivatives.
Read this article to find out more about Kekulé’s insight into benzene’s structure.
What are the rules for determining if a compound is aromatic? It’s more than just a sweet smell.
Watch this video for a nice overview of the Birch Reduction, including a demonstration!
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