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. Some physical and chemical properties of benzene are mentioned below:
Physical and chemical properties of benzene:
- Benzene belongs to the family of aromatic hydrocarbons which are nonpolar molecules and are usually colourless liquids or solids with a characteristic aroma.
- Benzene being non-polar is immiscible with water but is readily miscible with organic solvents.
- 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.
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.
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.
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 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.
Addition reactions: Addition of chlorine in the presence of ultraviolet light produces benzene hexachloride better known as gammaxene.
Combustion of benzene: Upon combustion of benzene, benzene burns with a sooty flame along with the evolution of CO2 gas.
C6H6 + O2 → CO2 + H2O
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