- Key People:
- Michael Faraday
- August Wilhelm von Hofmann
- Related Topics:
- hydrocarbon
- benzenoid aromatic compound
- Kekulé structure
- Dewar benzene
- benzene ring
benzene
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What is benzene?
Benzene ((C_6H_6)) is the simplest aromatic hydrocarbon and serves as the parent compound for many other aromatic compounds. Michael Faraday first isolated benzene in 1825 from oily residues of illuminating gas.
Benzene is a colorless, toxic liquid with a distinct odor and is mainly used to produce polystyrene. Exposure to benzene is known to cause leukemia, so its emissions are strictly controlled.
Modern bonding models explain benzene's stability through electron delocalization, where six electrons are attracted to all six carbon atoms in the ring. This makes benzene more stable and less reactive than expected.
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What does the chemical structure of benzene look like?
Benzene (C6H6) is the simplest aromatic hydrocarbon and consists of a ring of six carbon atoms with one hydrogen atom attached to each carbon.
In 1865, August Kekulé suggested a cyclic structure for benzene. The modern bonding models explain benzene's structure and stability using the concept of electron delocalization, where six electrons are attracted to all six carbon atoms in the ring. This delocalization makes benzene more stable and less reactive than expected for an unsaturated hydrocarbon.
Benzene is a planar molecule where all carbon-carbon bonds are equal in length, at 1.40 angstroms, which is between single and double bond distances, with all bond angles at 120°. This special stability is why benzene is less reactive than other unsaturated hydrocarbons.
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Where is benzene commonly found or used?
Benzene (C6H6) is a colorless, aromatic hydrocarbon primarily sourced from petroleum-based processes, replacing older coal tar methods. It serves as a parent compound for many aromatic compounds.
More than half of produced benzene is converted into ethylbenzene, then into styrene, and then into polystyrene. Benzene is also used to prepare phenol, aniline (for dyes), and dodecylbenzene (for detergents). Due to its toxicity and carcinogenic properties, including the risk of leukemia, strict controls regulate its emissions. Benzene is also used in the production of synthetic fibers, coatings, plastics, and elastomers.
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Why is benzene considered an important chemical in industry?
Benzene is an important industrial chemical with varied uses. Over half of the benzene produced annually is converted into ethylbenzene, which is then made into styrene and then polystyrene. Benzene is also used in the production of phenol, aniline for dyes, and dodecylbenzene for detergents. The stability of the benzene ring makes it possible to convert alkanes to arenes, which are then used as starting materials for plastics, fibers, dyes, agricultural chemicals, and drugs.
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What are some health risks of being exposed to benzene?
Benzene is a toxic, colorless liquid primarily used in polystyrene production. Exposure to benzene poses significant health risks, including depression of the central nervous system, which can cause drowsiness. Long-term exposure can severely damage organs like bone marrow, potentially leading to the development of leukemia, a type of cancer. Strict regulations are in place to control benzene emissions due to its carcinogenic properties.
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How did scientists discover the structure of benzene?
The structure of benzene has been of interest to scientists since its discovery in 1825 by Michael Faraday. In 1865, August Kekulé suggested a cyclic structure for benzene. In 1872, Kekulé revised his proposal, suggesting that two structures interconvert rapidly.
Later, in 1931, Linus Pauling used the concept of resonance to describe benzene's structure. According to the resonance model, benzene has a single structure that is a hybrid of two Kekulé forms, with six delocalized (\pi) electrons shared by all six carbon atoms. Experimental studies show that benzene has a planar structure with equal carbon-carbon bond distances, supporting the idea of electron delocalization.
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benzene (C6H6), simplest organic, aromatic hydrocarbon and parent compound of numerous important aromatic compounds. Benzene is a colourless liquid with a characteristic odour and is primarily used in the production of polystyrene. It is highly toxic and is a known carcinogen; exposure to it may cause leukemia. As a result, there are strict controls on benzene emissions.
Discovery of benzene
Benzene was first discovered by the English scientist Michael Faraday in 1825 in illuminating gas. In 1834 German chemist Eilhardt Mitscherlich heated benzoic acid with lime and produced benzene. In 1845 German chemist A.W. von Hofmann isolated benzene from coal tar.
The structure of benzene has been of interest since its discovery. German chemists Joseph Loschmidt (in 1861) and August Kekule von Stradonitz (in 1866) independently proposed a cyclic arrangement of six carbons with alternating single and double bonds. Kekule subsequently modified his structural formula to one in which oscillation of the double bonds gave two equivalent structures in rapid equilibrium. In 1931 American chemist Linus Pauling suggested that benzene had a single structure, which was a resonance hybrid of the two Kekule structures.
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Characteristics of benzene
Modern bonding models (valence-bond and molecular orbital theories) explain the structure and stability of benzene in terms of delocalization of six of its electrons, where delocalization in this case refers to the attraction of an electron by all six carbons of the ring instead of just one or two of them. This delocalization causes the electrons to be more strongly held, making benzene more stable and less reactive than expected for an unsaturated hydrocarbon. As a result, the hydrogenation of benzene occurs somewhat more slowly than the hydrogenation of alkenes (other organic compounds that contain carbon-carbon double bonds), and benzene is much more difficult to oxidize than alkenes. Most of the reactions of benzene belong to a class called electrophilic aromatic substitution that leave the ring itself intact but replace one of the attached hydrogens. These reactions are versatile and widely used to prepare derivatives of benzene.
Experimental studies, especially those employing X-ray diffraction, show benzene to have a planar structure with each carbon-carbon bond distance equal to 1.40 angstroms (Å). This value is exactly halfway between the C=C distance (1.34 Å) and C—C distance (1.46 Å) of a C=C—C=C unit, suggesting a bond type midway between a double bond and a single bond (all bond angles are 120°). Benzene has a boiling point of 80.1 °C (176.2 °F) and a melting point of 5.5 °C (41.9 °F), and it is freely soluble in organic solvents, but only slightly soluble in water.
Uses of benzene
At one time, benzene was obtained almost entirely from coal tar; however, since about 1950, these methods have been replaced by petroleum-based processes. More than half of the benzene produced each year is converted to ethylbenzene, then to styrene, and then to polystyrene. The next largest use of benzene is in the preparation of phenol. Other uses include the preparation of aniline (for dyes) and dodecylbenzene (for detergents).