Benzene

Introduction

In the past, gum benzene, also known as "Benjamin," was the source of the word benzene. An aromatic resin was thought to be gum benzoin. English scientist Michael Faraday made the initial discovery of benzene in lighting gas. German chemist Mitscherich gave benzene its name in 1833. German professor August Kekule solved the puzzle of the cyclic structure of benzene in 1865. Professor Linus Pauling from the United States claims that benzene has a hybrid structure made up of delocalized electrons. Kekule's findings were enhanced in this way.

What is Benzene?

Benzene, a colourless compound with the molecular formula, $\mathrm{C_{6}H_{6}}$ has a unique odour. Six carbon atoms are joined together in benzene's ring-closed structure by alternating single and double bonds. A single hydrogen atom groups each carbon atom. At 5.5°C, benzene melts, and at 80.1°C, it boils. An important class of chemical compounds known as aromatic compounds includes benzoene and its derivatives. Because of this, benzene is substantially more difficult to oxidise than alkenes and hydrogenates much more slowly than other organic compounds with carbon-carbon double bonds. The sort of reaction that produces most benzene reactions is an aromatic electrophilic substitution that replaces one of the hydrogen atoms connected to it while maintaining the structure of the ring. Pharmaceuticals, plastics, oils, synthetic rubbers, and paints all employ benzoene as a basic ingredient.

At room temperature, benzene is a liquid substance that is colourless or light yellow. In the chemical and pharmaceutical sectors, it is largely utilised as a solvent. Forest fires and volcanoes are two instances of benzene's natural sources. Naturally occurring benzene is present in crude oil, gasoline, and cigarette smoke. In some industries, benzene is used to make other compounds that are utilised to make synthetic fibres like nylon, plastics, and resins. In addition, benzene is used to make a variety of lubricants, rubbers, dyes, detergents, pharmaceuticals, and insecticides.

Structure of Benzene?

The structural representation of benzene is typically a six-carbon ring with three double bonds. A corner indicates one carbon atom per connection between two other atoms. In the chemical molecule benzene, these atoms are hydrogens. Because the double bonds are separated by single bonds, we may determine that the arrangement involves conjugated double bonds. A circle inside a hexagon is a different way to depict the six pi electrons. Each of these images carries both positive and negative characteristics.

Physical properties of benzene

• The chemical compound known as benzene is colourless and liquid.

• The melting point of benzene is 5.5 °C, and 80.1 °C is the melting point ofbenzene.

• Benzene is soluble in certain organic solvents but benzene is not miscible in water.

• The smell of benzene is aromatic.

• The density value of benzene is 0.87 gm/cm³.

• Resonance is present in benzene.

• Benzene is non-flammable and burns with sooty flames.

Chemical properties of benzene

• Nitric acid and benzene interact at a temperature between 323K and 333K to form nitrobenzene when sulfuric acid is present.

• Benzene Sulfonation - It is a procedure where fuming sulphuric acid is heated with benzene to create benzene sulphuric acid. The reaction can be stopped

• Benzene's halogenation - Benzene interacts with the halogens to produce aryl halides when Lewis acids ( $\mathrm{FeCl_{2}}$,$\mathrm{FeBr_{2}}$ ) are present (X - halogens)

  

• In the Friedel Craft Alkylation Reaction, benzene undergoes an alkyl halide reaction to generate alkylbenzene when any Lewis acid is present.

• The Friedel-Craft Acylation Reaction occurs when an acyl halide reacts with benzene to form acyl benzene when there is any Lewis acid present.

  

• Benzene combustion: Benzene burns with a sooty flame and releases $\mathrm{CO_{2}}$ when it is burned.

$$\mathrm{C_{6}H_{6}+O_{2}\to CO_{2}+H_{2}O}$$

Resonance of Benzene

The concept of hybridization is the idea of joining two atomic orbitals to form a completely new class of hybridised orbitals. Hybrid orbitals with completely different energies, shapes, etc. are typically produced by this mixing. When a single Lewis structure is insufficient to properly explain the bonding, resonance structures are used. A resonance hybrid, which depicts the total delocalization of electrons inside the molecule, is defined as the mixture of possible resonance structures.

These resonance structures and valence bond theory are used to explain the oscillating double bonds in the benzene ring. The benzene ring has $\mathrm{sp^{2}}$ hybridised carbon atoms throughout. Six $\mathrm{C-C}$ sigma bonds are created when one of an atom's two $\mathrm{sp^{2}}$ hybridised orbitals coincides with the $\mathrm{sp^{2}}$ orbital of a nearby carbon atom. Six $\mathrm{C-H}$ sigma bonds are created when other left $\mathrm{sp^{2}}$hybridised orbitals come along with the hydrogen s orbital. By lateral overlap, the carbon atoms' remaining unhybridized p orbitals create bonds with their neighbouring carbon atoms.

Preparation of Benzene

For the production of benzene, numerous industrial and laboratory processes are available. Commercially, coal tar is the main source of benzene. The following is a discussion of some benzene preparation methods used in laboratories

• Cyclic polymerization is one of the methods used to create benzene from ethyne. Ethyne is put through a red-hot iron tube at 873 K in this procedure. Following this, the ethyne molecule goes through cyclic polymerization to create benzene.

  

• Through a decarboxylation reaction, benzene can be produced from aromatic acids. In this procedure, benzene and sodium carbonate are created by heating the sodium salt of benzoic acid (Sodium Benzoate) with soda lime.

  

• Additionally, phenols can be reduced to produce benzene. In this procedure, heated zinc dust is passed over phenol vapours. They are reduced to benzene by zinc dust.

  

• Through the hydrolysis of sulphonic acids, benzene can be produced. This procedure results in the creation of benzene by exposing benzene sulphonic acid to extremely hot steam.

$$\mathrm{C_{6}H_{5}-SO_{3}H+H_{2}O \to C_{6}H_{6}+H_{2}SO_{4}}$$

Uses of Benzene

Benzene is used in several industry segments. Benzene, a chemical that is widely used in industry, can be found in substantial amounts in petroleum. Benzene also finds usage in the production of synthetic fibres, rubber lubricants, dyes, resins, detergents, and more. The list and discussion of a few well-known ones can be found below.

• Benzene is widely used as an industrial solvent.

• Rubber and tyre production frequently involve the use of benzene.

• Products used to sanitise printing equipment are the main sources of benzene. The printing equipment is made durable and adequately functional by the use of benzene in cleaning chemicals.

• A crucial ingredient in the production of gasoline is benzene. The majority of the products made by oil refineries contain benzene, which makes up a significant portion of crude oil.

• The manufacturing of lubricants used in the production industries' heavy machinery maintenance involves the usage of benzene.

Conclusion

Benzene is a transparent, colourless, and very flammable organic chemical compound. It is an aromatic substance with a pleasant smell. Six carbon atoms are bonded together to form the ring-shaped structure of a benzene molecule, and each carbon atom is connected to a hydrogen atom. Benzene is classified as a hydrocarbon since its only two constituent atoms are carbon and hydrogen. Numerous additional aromatic compounds are known to have benzene as their parent substance.

FAQs

Q1. Is benzene basic or acidic?

Ans. Following Lewis' theory about different acids and bases, which states that an acid always takes electrons and a base always gives electrons. Since it donates a pair of electrons, benzene is a base.

Q2. Name any three benzene-containing foods?

Ans. Cocktails, pineapple crush, and other beverages contain benzene in it.

Q3. What are the critical stages in industrial benzene production?

Ans. The commercial production of benzene is mostly carried out by Catalytic reformation, toluene hydrodealkylation and steam cracking.

Q4. Is benzene dangerous to people?

Ans. The chemical benzene does indeed pose some health risks. Constant benzene exposure causes irritation, severe headaches, and unconsciousness. It is also carcinogenic.

Q5. What occurs when you smell benzene?

Ans. Short-term inhalation exposure to benzene can cause fatigue, headaches, eye, skin, and respiratory tract irritation in humans, as well as comma at high doses.