Introduction to Benzene: preparation, properties, reactivity and uses

Written by Adeel Abbas

Benzene is an aromatic compound that is widely used in the chemical industry. It is a cyclic hydrocarbon with a unique stability and reactivity towards difference reagents.

Discovery of benzene

The discovery of benzene is generally attributed to the German chemist Friedrich August Kekulé. In the 1850s and 1860s, Kekulé proposed that the carbon atoms in benzene were arranged in a ring, with alternating double bonds. He also proposed that these double bonds were delocalized, meaning that the electrons in the double bonds were spread out over multiple atoms.

Kekule structure of benzene

Kekulé’s proposed structure for benzene was groundbreaking at the time, as it helped to explain many of the properties of the compound, such as its stability and reactivity. His work on benzene was a major step forward in the field of organic chemistry and helped to establish the field of structural chemistry.

Kekulé’s structural model for benzene was further confirmed by the work of other chemists, such as Joseph Loschmidt, who proposed a similar structure for benzene, and by later experimental evidence, such as the results of X-ray diffraction studies.

image showing kekule structures and stability of benzene

Methods for Preparation of benzene

Benzene can be prepared through four methods that are common in the industry.

1. Cyclic polymerization of AlkynesEthyne passes through a tube of red-hot iron at 873K
2. Decarboxylation of Aromatic AcidsSodium salt of Benzoic acid is heated with Soda Lime
3. Reduction of PhenolsVapors of Phenol pass over heated dust of Zinc
4. Hydrolysis of Sulphonic AcidsSulphonic acid is exposed to heated steam

Stability of Benzene ring

One of the unique characteristics of benzene is its stability. The electrons in the aromatic ring are delocalized, meaning they are spread out over multiple atoms rather than being localized on a single atom. This delocalization results in a stabilization of the ring, making it less reactive than alkenes.

Physical properties of benzene

Molecular FormulaC6H6
Molecular Weight78.11 g/mol
Density0.87 g/cm3
Melting Point5.5 °C
Boiling Point80.1 °C
Solubility in WaterInsoluble
Refractive Index1.501
Vapor Pressure43 mmHg at 20 °C
Flash point-11 °C
Autoignition temperature446 °C

Chemical properties of benzene

Benzene possess unique chemical properties. There are certain factors that imparts the reactivity into benzene ring. Let us discuss these in detail.

Aromaticity: Benzene is a highly aromatic compound and exhibits resonance stabilization. This means that the electrons in the ring are distributed evenly around the ring and are delocalized, making it more stable and less reactive than other molecules with similar structures.

Reactivity: Despite its aromatic nature, benzene is relatively unreactive towards electrophilic reagents. This is due to the electron-withdrawing effect of the ring’s double bonds, which make the ring less electrophilic. However, it can undergo nucleophilic substitution reactions and electrophilic substitution reactions with a certain reagents such as bromine in the presence of a Lewis acid catalyst.

Oxidation: Benzene is resistant to oxidation and does not easily react with oxygen.

Pyrophoric: Benzene is pyrophoric, which means that it may spontaneously ignite in air.

Toxicity: Benzene is toxic and exposure to high concentrations can have negative effects on human health, including anemia, leukemia and other blood disorders.

Benzene undergoes following types of reactions.

Electrophilic Substitution Reactions

One of the most common reactions of benzene is electrophilic substitution. In this type of reaction, an electrophile (an atom or molecule with a positive or partial positive charge) replace a functional group in the aromatic ring of benzene. This results in the formation of a new compound, with the electrophile replacing one of the hydrogens on the ring.

Nucleophilic Substitution Reactions

Benzene can also undergo nucleophilic substitution reactions. In this type of reaction, a nucleophile (an atom or molecule with a negative or partial negative charge) attacks the electrophilic center of an benzene ring. In the case of benzene, the nucleophile attacks a carbocation that is formed when an electrophile attacks the aromatic ring.

Examples of nucleophilic substitution reactions of benzene

  • Reduction of nitrobenzene to aniline: Nitrobenzene is reduced by a nucleophile, such as hydrazine, to form aniline.
  • Reduction of diazonium compounds to phenols: Diazonium compounds, such as benzenediazonium chloride, are reduced by a nucleophile, such as hydroxide ion, to form phenols.
  • Hydrolysis of alkylbenzenes: Alkylbenzenes, such as toluene, undergo hydrolysis in the presence of a nucleophile, such as water, to form benzoic acid and the corresponding alcohol.

Addition Reactions

Benzene can also undergo addition reactions. In this type of reaction, a compound is added across the double bond of the ring. This can happen via electrophilic or nucleophilic addition.

One example of electrophilic addition reaction is hydrogenation of benzene to cyclohexane. In the presence of a catalyst such as nickel, hydrogen adds across the double bond of the ring and forming a saturated cyclic hydrocarbon, cyclohexane

Another example of addition reaction is electrophilic addition of chlorine to form chlorobenzene. In the presence of Lewis acid catalyst, chlorine adds to the double bond of the ring forming chlorobenzene.

Benzene is a unique and widely used compound in the chemical industry. Its stability and reactivity make it a versatile starting material for a wide range of reactions. Understanding the different types of reactions that benzene can undergo, such as electrophilic substitution, nucleophilic substitution, and addition reactions, is crucial for understanding its properties and applications.

Summary of Benzene reactions

Reaction TypeExampleMechanismProduct
Electrophilic SubstitutionHalogenationElectrophile (X2 or XBr) attacks the ring in the presence of Lewis acid catalystAr-X (Ar is the substituent)
NitrationNitronium ion (NO2+) attacks the ring in the presence of sulfuric acidAr-NO2
Nucleophilic SubstitutionReduction of NitrobenzeneNucleophile(NH2NH2) attacks the electrophilic center of the nitro groupAr-NH2
AdditionHydrogenationHydrogen added across the double bond in the presence of a catalystCyclohexane
ChlorinationChlorine added across the double bond in the presence of a Lewis acid catalystChlorobenzene


Ar indicates benzene ring attached with an other electrophile.

The specific conditions and catalysts for each reaction can vary depending on the exact process being used.

Uses of Benzene

SolventIndustrial and commercial, used as absorbing and binding agent
Rubber ProductionTires, rubber products
Paints and PrintingCleaning equipment, inks, dyes, lacquers, stains, sealers
Fuelgasoline, lubricants, asphalt
Chemical and Plastic ProductionResins, adhesives, synthetic fibers, detergents, dyes, insecticides, pesticides and herbicides
Auto RepairsCleaning and maintenance of machinery
PharmaceuticalsProduction of drugs and medications
AgriculturePesticides and fertilizers
ElectronicsProduction of semiconductors
Food and Beverage IndustryAdditives and preservatives
AdhesivesGlues and sealant production
Synthetic fragrancesperfumes and other scented products
Explosives and FireworksTNT, dynamite, and other explosive materials