Benzena dan Turunannya • Part 4: Reaksi Adisi dan Substitusi Benzena

Summary

This video dives into benzene and its derivatives, explaining key reactions such as addition and substitution. It covers how benzene reacts with hydrogen, chlorine, and other reagents like halogens, alkyl groups, and nitro groups, introducing various types of reactions like halogenation, alkylation, nitration, and sulfonation. The video emphasizes that benzene is more likely to undergo substitution than addition due to its resonance structure. Practical examples of each reaction are given, with clear explanations of mechanisms and products. The video is designed for high school students learning organic chemistry and aims to clarify complex topics in a simplified manner.

Takeaways

• 😀 Benzene is more likely to undergo substitution reactions than addition reactions due to its resonance structure.
• 😀 Addition reactions of benzene include hydrogenation (with H₂ and nickel catalyst) to form cyclohexane and chlorination (with Cl₂ and UV light) to form hexachlorocyclohexane.
• 😀 In substitution reactions, benzene’s hydrogen atoms are replaced by other groups like halogens, alkyl groups, and acyl groups.
• 😀 Halogenation involves the replacement of a hydrogen atom in benzene with a halogen (X), such as chlorine, forming halobenzene.
• 😀 Alkylation reacts benzene with an alkyl halide (like methyl chloride) and AlCl₃ catalyst, replacing a hydrogen atom with an alkyl group to form alkyl benzene (e.g., toluene).
• 😀 Nitration is the reaction of benzene with nitric acid and sulfuric acid, introducing a nitro group (-NO₂) to form nitrobenzene.
• 😀 Sulfonation of benzene with sulfuric acid and an SO₃ catalyst replaces a hydrogen atom with a sulfonic acid group (-SO₃H), resulting in benzene sulfonic acid.
• 😀 Acylation of benzene uses acyl halides (like acetyl chloride) with AlCl₃ as a catalyst to replace a hydrogen atom with an acyl group, forming aromatic ketones like acetylbenzene.
• 😀 In a halogenation reaction with bromine and FeCl₃ catalyst, benzene forms bromobenzene, and HBr is produced as a byproduct.
• 😀 In alkylation, methyl chloride reacts with benzene and AlCl₃ catalyst to form toluene, with HCl as the byproduct.
• 😀 A nitration reaction introduces a nitro group to benzene using nitric acid and sulfuric acid, resulting in nitrobenzene and water as a byproduct.

Q & A

Why is benzene more likely to undergo substitution reactions rather than addition reactions?

Benzene undergoes substitution reactions more readily because its resonance structure stabilizes the double bonds, making it harder for the molecule to react via addition, which would break these bonds. The resonance makes benzene less reactive to addition but still reactive enough for substitution reactions.

What happens during the hydrogenation of benzene?

In hydrogenation, benzene reacts with hydrogen gas (H₂) in the presence of a nickel or Eni catalyst at 150°C. This reaction breaks the double bonds of the benzene ring, resulting in the formation of cyclohexane.

What is hexachlorocyclohexane, and how is it formed from benzene?

Hexachlorocyclohexane is formed when benzene reacts with chlorine gas (Cl₂) under UV light. This results in the substitution of hydrogen atoms in the benzene ring with chlorine atoms, leading to the formation of a cyclohexane ring with six chlorine atoms attached.

What is a halogenation reaction involving benzene?

A halogenation reaction occurs when benzene reacts with a halogen (X₂, like chlorine or bromine) in the presence of a catalyst like FeCl₃. This reaction replaces one of the hydrogen atoms in the benzene ring with a halogen atom, forming a halobenzene and producing HX (like HCl or HBr) as a byproduct.

What is the role of FeCl₃ in the halogenation of benzene?

FeCl₃ acts as a catalyst in the halogenation reaction, facilitating the generation of the reactive halogen species that enables the halogen atom to substitute for a hydrogen atom in the benzene ring.

How does alkylation of benzene occur, and what product is formed?

In alkylation, benzene reacts with an alkyl halide (like methyl chloride, CH₃Cl) in the presence of an AlCl₃ catalyst. The alkyl group (e.g., CH₃) replaces a hydrogen atom in the benzene ring, forming alkylbenzene (e.g., toluene, CH₃C₆H₅) as the product.

What is the byproduct of the alkylation of benzene?

The byproduct of the alkylation of benzene is typically hydrogen chloride (HCl), which is expelled when the alkyl group replaces the hydrogen atom in the benzene ring.

Explain the nitration reaction of benzene and its product.

In the nitration reaction, benzene reacts with nitric acid (HNO₃) in the presence of sulfuric acid (H₂SO₄) as a catalyst. This results in the substitution of a hydrogen atom with a nitro group (NO₂), forming nitrobenzene (C₆H₅NO₂). The byproduct of this reaction is water (H₂O).

What happens in the sulfonation reaction of benzene?

During sulfonation, benzene reacts with sulfuric acid (H₂SO₄) in the presence of a catalyst (SO₃). This results in the substitution of a hydrogen atom in the benzene ring with a sulfonic acid group (SO₃H), producing benzene sulfonic acid (C₆H₅SO₃H). The byproduct is water (H₂O).

How is acetylbenzene formed in the acylation reaction with benzene?

In the acylation reaction, benzene reacts with acetyl chloride (CH₃COCl) in the presence of AlCl₃ as a catalyst. The acetyl group (CH₃CO) replaces a hydrogen atom in the benzene ring, forming acetylbenzene (C₆H₅COCH₃). The byproduct is hydrochloric acid (HCl).