BENZENA PART 2 : SIFAT FISIS DAN KIMIA BENZENA

Summary

This video delves into the physical and chemical properties of benzene, a nonpolar compound that is insoluble in polar solvents like water but dissolves in non-polar solvents. It discusses its volatility, toxicity, and chemical reactions, including oxidation, substitution (nitration, sulfonation, halogenation, alkylation, and acylation), and addition reactions (hydrogenation and halogenation). The video also explains how these reactions, involving catalysts, lead to various benzene derivatives and highlight its relatively low reactivity due to conjugated resonance bonds.

Takeaways

• 😀 Benzene is a nonpolar compound, making it insoluble in polar solvents like water but soluble in nonpolar solvents such as carbon tetrachloride, diethyl ether, acetone, and hexane.
• 😀 Benzene is a colorless liquid with a distinct odor, a melting point of 5.5°C, and a boiling point of 80.1°C.
• 😀 Benzene vapor is toxic and slightly carcinogenic, making it hazardous to handle.
• 😀 Due to its conjugated π-electrons, benzene is less reactive and typically requires a catalyst for most chemical reactions.
• 😀 The main substitution reactions of benzene include nitration, sulfonation, halogenation, alkylation, and acylation.
• 😀 In nitration, benzene reacts with concentrated nitric acid (HNO₃) and sulfuric acid (H₂SO₄) to form nitrobenzene.
• 😀 In sulfonation, benzene reacts with sulfur trioxide (SO₃) in the presence of sulfuric acid (H₂SO₄) to form benzenesulfonic acid.
• 😀 Halogenation involves benzene reacting with halogens (e.g., Cl₂, Br₂) using a Lewis acid like FeCl₃ to form halogenated benzene.
• 😀 Alkylation (Friedel-Crafts reaction) occurs when benzene reacts with an alkyl halide (e.g., CH₃Cl) in the presence of AlCl₃ to form alkylated benzene (e.g., toluene).
• 😀 Acylation (also a Friedel-Crafts reaction) involves benzene reacting with an acyl halide (e.g., CH₃COCl) in the presence of AlCl₃ to form an acylated benzene (e.g., acetophenone).
• 😀 Addition reactions of benzene include hydrogenation (conversion to cyclohexane) and halogen addition under photochemical conditions, forming hexachlorocyclohexane.

Q & A

What are the physical properties of benzene?

Benzene is a non-polar compound, insoluble in polar solvents like water but soluble in non-polar solvents such as carbon tetrachloride, diethyl ether, acetone, and hexane. It is a colorless liquid with a characteristic odor and is volatile. Its melting point is around 5.5°C, and its boiling point is 81°C.

Why is benzene considered less reactive?

Benzene is less reactive because of its conjugated bonds, which experience resonance. This resonance stabilizes the molecule, making it less likely to participate in reactions unless a catalyst is used.

What are the safety concerns associated with benzene vapor?

Benzene vapor is toxic and mildly carcinogenic, posing health risks when inhaled or when there is prolonged exposure.

What happens when benzene undergoes complete oxidation?

When benzene is completely oxidized, it produces carbon dioxide and water. The reaction also generates soot due to the formation of carbon particles.

What is the nitration reaction of benzene, and what does it produce?

The nitration reaction involves benzene reacting with concentrated nitric acid (HNO₃) in the presence of sulfuric acid (H₂SO₄) at around 50°C. This reaction produces nitrobenzene.

How does sulfonation of benzene occur, and what is the product?

In the sulfonation reaction, benzene reacts with fuming sulfuric acid (H₂SO₄ and SO₃) to replace a hydrogen atom with a sulfonic acid group, producing benzenesulfonic acid.

What is the role of FeCl₃ in halogenation of benzene?

FeCl₃ acts as a catalyst in the halogenation of benzene, facilitating the substitution of a hydrogen atom by a halogen (e.g., chlorine) to form a halobenzene.

Explain the Friedel-Crafts alkylation reaction with benzene.

In the Friedel-Crafts alkylation, benzene reacts with a haloalkane (e.g., CH₃Cl) in the presence of AlCl₃ as a catalyst. This reaction substitutes a hydrogen atom with an alkyl group, producing alkylbenzenes like toluene.

What is the difference between alkylation and acylation reactions of benzene?

In alkylation, benzene reacts with a haloalkane to form alkylbenzenes, while in acylation, benzene reacts with an acyl halide (e.g., CH₃COCl) to form acylated products like acetophenone. Both reactions require AlCl₃ as a catalyst.

What is the result of hydrogenation of benzene, and what conditions are required?

Hydrogenation of benzene converts it into cyclohexane. This reaction requires a catalyst, such as nickel (Ni), and high temperature (420K).

How does the halogenation of benzene occur under photochemical conditions?

In the halogenation of benzene under photochemical conditions, benzene reacts with halogens like Cl₂ in the presence of light (photons), breaking the conjugated double bonds and forming halogenated cyclohexane derivatives like hexachlorocyclohexane.