Benzene is a simple cyclic aromatic compound, which is made of hydrogen and oxygen. Benzene consists of an equal number of hydrogen and oxygen atoms. The formula of Benzene is C₆H₆. The structure of benzene is a closed ring-like structure that resembles a hexagon with alternate single and double bonds between the carbon atoms.

Benzene is an important compound in Organic Chemistry as many compounds are derived from this using various reactions. Benzene has ill health effects in case of overexposure.

In this article, we are going to learn what benzene is, where benzene is found, the discovery of benzene, the characteristics of benzene, uses of benzene, and the ill effects of benzene on health in detail.

What is Benzene?

Benzene is an aromatic organic compound. It is a colourless liquid. Benzene has a sweet odor. Benzene is an organic aromatic hydrocarbon. It evaporates into the air very quickly and dissolves slightly in water. It is highly flammable and is formed from both natural processes and human activities. Benzene is a closed ring of six carbon atoms linked by bonds that alternate between single and double bonds. Each carbon atom is bound by a single hydrogen atom. Benzene melts at a temperature of 5.5 ° C and boils at 80.1°C. Benzene shows resonance properties. Benzene burns with a sooty flame.

Benzene Chemical Formula

Chemical formula of Benzene is C₆H₆

Benzene IUPAC Name

IUPAC Name of Benzene is cyclo-hex-1,3,5-triene

Benzene Molar Mass

Molar mass of Benzene is 78 atomic mass unit.

Chemical formula of Benzene is C₆H₆.

Atomic mass of carbon is 12 unit

Atomic mass of hydrogen is 1 unit.

Total atomic mass is 12 ⨉ 6 + 1 ⨉ 6 = 78 atomic mass unit.

Where is Benzene Found?

Benzene is formed from both natural processes and human activities. Manmade Benzene are found in glues, adhesives, cleaning products, paint strippers, tobacco smoke and gasoline. Benzene is produced naturally by volcanoes and forest fires. Most benzene in the environment comes from our use of petroleum products. Benzene is also found in detergents and paints.

Discovery Of Benzene

Benzene was discovered by scientist Michael Faraday in illuminating gas in 1825. The term benzene is derived from the term benzoin which was known as aromatic resin. In 1834 German chemist Eilhardt Mitscherlich heated benzoic acid with lime and produced benzene.

When Benzene was discovered its cyclic structure was not known, but in 1865 German professor August Kekule proposed its cyclic structure, snake biting its own tail. Further in 1861 German chemists Joseph Loschmidt and August Kekule in 1866 independently proposed a cyclic arrangement of six carbons with alternating sigma (single) and pi (double) bonds.

Kekule again modified his structure proposing two structure of benzene with oscillating double bonds. In 1931 American chemist Linus Pauling suggested that benzene had a single structure, which was a resonance hybrid of the two Kekule structures.

Structure of Benzene

Structure of Benzene is similar to hexagon. There are three sigma bonds present between carbon-carbon atom and three pi bonds present between carbon-carbon atom. The carbon atoms are represented by a corner that is bonded to other atoms. The double bonds in benzene are mainly separated by a single bond, hence this arrangement is recognized to have conjugated double bonds.

Structure of Benzene

What is Benzene Ring?

Benzene is a cyclic hydrocarbon compound in which 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, benzene ring involves the formation of three delocalized π–orbitals spanning all six carbon atoms. According to valence bond theory benzene has two stable resonance structures for the ring.

Resonance of Benzene

Kekule was the scientist who proposed two structure of Benzene. The two structure of Benzene differ in placement of alternate double bonds only. But, the original structure of benzene is hybrid of these two structure was confirmed in X-ray diffraction experiment. When many multiple lewis dot structure of a compound exist because of presence of double bond or lone pair then it forms a resonance structure. The more resonance forms a molecule has, the more stable the molecule is. They are connected by a double-headed arrow, indicating these two structure are resonance in nature. Benzene forms two resonance structure which makes this compound more stable. One hybrid structure of benzene represents oscillating double bond inside it i.e. not a fixed place of double bonds.

Resonance of Benzene

Characteristics of Benzene

Few characteristics of benzene are listed below:

• The formula of Benzene is C₆H₆.
• Benzene is a simple aromatic compound made of equal number of hydrogen (six atom) and carbon atom (six atom).
• Experimentally it was found by that benzene is planar in structure.
• The distance between carbon carbon double bond C=C is 1.34 Å , and distance between carbon carbon single bond is C-C is 1.46 Å. Boiling point of benzene is 80.1 °C and its melting point is 5.5 °C.
• The density of benzene is 0.87g cm-3.
• Benzene is freely soluble in organic solvents, but slightly soluble in water because benzene is non polar in nature.
• Benzene is good solvent for many organic and inorganic substances.
• Benzene is highly inflammable and burns with a sooty nature (luminous in nature).

Why Benzene is Aromatic?

To check if a given compound is aromatic or not we apply Huckel rule. In 1931, German chemist and physicist Erich Huckel proposed a theory to help and determine if a planar ring molecule would have aromatic properties. According to Huckel rule, for a ring to be aromatic it should satisfy the following properties mentioned below:

• Compound Should be planar.
• Complete delocalization of the π electrons in the ring.
• Presence of (4n + 2) π electrons in the ring where n is an integer (n = 0 , 1, 2, 3 ……….).

If we check above three properties for Benzene, benzene satisfies all the three properties.

• Benzene is a planar compound
• It has delocalized π electrons over the ring.
• Benzene has 6 π electron which is equal to (4n+2) π electron if we put n = 1.

Hence, Benzene is an aromatic compound.

Properties of Benzene

The properties of benzene is classified into following

• Physical Properties
• Chemical Properties

Physical Properties of Benzene

The physical properties of Benzene are mentioned below

Chemical Properties of Benzene

The chemical properties of Benzene are mentioned below:

Derivatives Compounds from Benzene

Some of derivatives of benzene are listed below:

• Ethyl benzene
• Phenol (hydroxy benzene)
• Aniline (amino benzene)
• Sodium dodecylbenzene sulphonate
• Toluene (methyl benzene)
• Cumene (isopropyl benzene)
• Chlorobenzene
• Styrene (vinyl benzene)
• Benzamide
• Nitrobenzene
• Ortho-xylene
• Meta-xylene
• Para-xylene
• Benzoic acid
• Benzaldehyde
• Anisole
• Methyl benzoate
• o-Bromo ethylbenzene
• p-Bromo nitrobenzene
• m-nitrobenzoic acid

Phenol

Though both alcohols and phenols contain -OH group, their physical properties vary due to the presence of benzene ring in phenol. The presence of the benzene ring modifies the properties of phenol. Phenol is a white crystalline solid at room temperature. However, the crystals turn pink with time. The coloration is because of oxidation. Phenol has a characteristic odor. Phenol has a molecular mass of 94.11 g/mol.

Read More about Preparation of Phenol

Anisole

Anisole is an organic compound with the formula CH₃OC₆H₅. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances.

Toluene

Toluene is compound derived by substituting one hydrogen of benzene with methyl group i.e. CH3. Toluene is colorless and insoluble in water. Toluene is used as precursor in many organic reactions

Aniline

Aniline is formed by substituting a hydrogen atom in Benzene with amino group i.e. -NH2. Hence the molecular formula of aniline is C₆H₅NH₂. Aniline is simplest aromatic amine.

Chemical Reactions of Benzene

Benzene undergoes following reaction:

• Combustion Reaction
• Addition Reaction
• Friedel Craft Alkylation
• Friedel Craft Acylation
• Halogenation
• Nitration
• Sulfonation

Combustion of Benzene

Combustion is a process when one substance is burned in adequate amount of oxygen and produces heat and light energy. When benzene is burned in presence of sufficient amount of oxygen then it produces carbon dioxide (CO₂) and water (H₂O). When it is burned in less amount of oxygen then in produces carbon monoxide (CO).

C₆H₆(l) + 15O₂(g) → 12CO₂(g) + 6H₂O(l)

Addition Reaction of Benzene

Benzene is very stable compound due to its resonance structure. That’s why benzene does not addition reaction easily. As Benzene possess unique stability, though in strong condition benzene shows addition reactions. In this reaction 3 molecules of reactant react with 1 mole of benzene, which shows benzene structure shows three double bonds (π).

Halogenation

Benzene reacts with halogens such as bromine in the presence of lewis acid like FeCl₃ or FeBr₃ to form aryl halides. That’s why this reaction is known as halogenation of Benzene. This reaction can take place at room temperature.

C₆H₆ (in presence of FeCl₃ FeBr₃ at room temperature) → C₆H₅Br

Nitration

Benzene reacts with concentrated nitric acid at 323-333K in the presence of concentrated Sulphuric acid and concentrated nitric acid to form nitrobenzene.

C₆H₆ (in presence of concentrated H₂SO₄ + concentrated HNO₃) → C₆H₅NO₂

Sulfonation

In sulfonation of benzene it is heated with fuming Sulphuric acid and produces Benzenesulfonic acid. This reaction is reversible in nature.

C₆H₆ (in presence of H₂SO₄ and SO₃) ⥦ Benzenesulfonic acid

Friedel Craft Alkylation

Friedel-Crafts Alkylation refers to the replacement of an aromatic proton with an alkyl group. This is done through an electrophilic attack on the aromatic ring with the help of a carbocation. The Friedel-Crafts alkylation reaction is a method of generating alkylbenzenes by using alkyl halides as reactants.

Friedel-Crafts Acylation

The Friedel-Crafts acylation reaction involves the addition of an acyl group to an aromatic ring. Typically, this is done by employing an acid chloride (R-(C=O)-Cl) and a Lewis acid catalyst such as AlCl₃. In a Friedel-Crafts acylation reaction, the aromatic ring is transformed into a ketone.

Uses of Benzene

Benzene is toxic in nature and very harmful of living beings. That’s why its use is limited in various manufacturing industries. Some of the usage of benzene are listed below:

• Benzene is used in manufacture of dyes.
• It is used in manufacture of lubricants.
• It used in manufacture of plastics.
• It is used in manufacture of synthetic fibers.
• It is used for manufacturing of nylon fibers.
• It is used in the preparation of phenol.

Bad Health Effects of Benzene

As mentioned above benzene is toxic in nature. Even high level of benzene can cause death of living beings. Various Bad side-effects of benzene on living beings are listed below:

• Inhalation of high levels of benzene results in headaches, dizziness, nausea, convulsions, coma and eventually death.
• Short-term inhalation of benzene in air can cause headaches, drowsiness, confusion and unconsciousness.
• Skin contacts with benzene can cause dryness and itching.
• Benzene cause causes irritation to the eyes and upper respiratory tract.
• Benzene is a carcinogen that also damages bone marrow and the central nervous system.
• Benzene can cause bone marrow not to produce enough red blood cells, which can lead to anemia.
• Benzene can damage the immune system by changing blood levels of antibodies and causing the loss of white blood cells

Also, Check

• Pyridine
• Haloalkanes and Haloarenes
• Kolbe Reaction

Benzene – FAQs

1. Why Benzene is Slightly Soluble in Water?

Benzene is a non polar liquid, so it is soluble in organic solvents only. When mixed with water which is a polar solvent it does not dissolve into it. It is slightly soluble because of ion-dipole interaction.

2. What is the Shape of Benzene?

Benzene has a closed ring like structure with alternate single and double bond in it.

3. How many Sigma and Pi Bonds are there in Benzene?

There are 12 sigma and three pi bonds in Benzene.

4. Is Benzene an Aromatic Compound?

Yes, Benzene is an Aromatic Compound.

5. How does the Two Resonance Structure of Benzene differ from each other?

The two structure of Benzene differ in placement of alternate double bonds only. But, the original structure of benzene is hybrid of these two structure was confirmed in X-ray diffraction experiment.

6. Which Scientist Isolated Benzene from Coal Tar?

In 1845 German chemist A.W. von Hofmann isolated benzene from coal tar.

7. Where is Benzene produced Naturally?

Benzene is a naturally occurring substance produced by volcanoes and forest fires and present in many plants and animals.