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Benzene: Physical and Chemical Properties

What is Benzene?

Benzene is a cyclic hydrocarbon with a chemical formula C6H6, that is, each carbon atom in benzene is arranged in a six-membered ring and is bonded to only one hydrogen atom.

According to molecular orbital theory for benzene structure, benzene ring involves the formation of three delocalized π – orbitals spanning all six carbon atoms, while the valence bond theory describes two stable resonance structures for the ring.

Benzene is one of the most fundamental compounds used in the manufacturing of various plastics, resins, synthetic fibers, rubber lubricants, dyes, detergents, drugs, and pesticides. Benzene is found to exhibit a unique set of physical and chemical properties.

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Some physical and chemical properties of benzene are mentioned below:

Physical Properties of Benzene:

  1. Benzene belongs to the family of aromatic hydrocarbons which are nonpolar molecules and are usually colourless liquids or solids with a characteristic aroma.
  2. Benzene being non-polar is immiscible with water but is readily miscible with organic solvents.
  3. Upon combustion of benzene sooty flame is produced.

Chemical Properties of Benzene:

Electrophilic substitution reaction:

Nitration of Benzene: Benzene reacts with nitric acid at 323-333 K in the presence of sulphuric acid to form nitrobenzene. This reaction is known as nitration of Benzene.

Nitration of Benzene

Sulfonation of Benzene: Sulfonation of benzene is a process of heating benzene with fuming sulphuric acid (H2SO4 +SO3) to produce Benzene sulphuric acid. The reaction is reversible in nature.

Sulfonation of Benzene

Halogenation of Benzene: Benzene reacts with halogens in the presence of Lewis acids like FeCl3, FeBr3 to form aryl halides. This reaction is termed as halogenation of benzene.

Halogenation of Benzene

Friedel Craft’s alkylation reaction: When benzene is treated with an alkyl halide in the presence of a Lewis acid such as anhydrous aluminium chloride, alkyl benzene is formed. This reaction is popularly known as Friedel Craft’s alkylation reaction.

friedel crafts alkylation

Friedel Craft’s acylation reaction: When benzene is treated with an acyl halide in the presence of Lewis acid such as anhydrous aluminum chloride, acyl benzene is formed. This reaction is popularly known as Friedel Craft’s acylation reaction.

friedel craft's acylation

Addition reactions: Addition of chlorine in the presence of ultraviolet light produces benzene hexachloride better known as gammaxene.

physical and chemical properties of benzene

Combustion of benzene: Upon combustion of benzene, benzene burns with a sooty flame along with the evolution of CO2 gas.

C6H6 + O2 → CO2 + H2O

Chlorobenzene is formed by the reaction of chlorine with benzene: During chlorination of benzene, anhydrous AlCl3, being a Lewis acid helps in generation of the electrophile Cl+ by combining with the attacking reagent.

The electrophile Cl+ attacks the benzene ring in this reaction.


Frequently Asked Questions – FAQs

Is benzene toxic to humans?

The Department of Health and Human Services has established that benzene is a recognized carcinogen (may cause cancer). Both the International Organization for Research on Cancer and the EPA have determined that benzene is carcinogenic to humans. Exposure to benzene can be harmful to reproductive organs.

What does benzene smell like?

Benzene has a sweet, aromatic, gasoline-like smell. Most individuals may begin to smell benzene in the air at 1.5 to 4.7 ppm. The odor threshold generally provides adequate warning for acutely hazardous exposure concentrations, but is insufficient for more chronic exposures.

Why is benzene so important?

Some essential chemical compounds are derived from benzene by substituting one or more of its hydrogen atoms for another functional group. Linking benzene rings are biphenyl, C6H5-C6H5. The depletion of hydrogen results in the formation of fused aromatic hydrocarbons such as naphthalene and anthracene.

Is benzene acidic or basic?

According to Lewis’ theory of acids and bases, an acid takes a pair of electrons and a base gives a pair of electrons, so benzene is a base since it gives a pair of electrons. Benzene is a base since it gives a pair of electrons.

What is the structure of C6H6?

The chemical formula of benzene is C6H6, consisting of six carbon atoms and six hydrogen atoms. Benzene is an aromatic hydrocarbon, a chemical compound composed of carbon and hydrogen atoms with alternating double bonds forming a ring.

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