Reactions of Arenes | 芳烃的反应

📚 Reactions of Arenes | 芳烃的反应

Arenes, also known as aromatic hydrocarbons, contain one or more benzene rings with a delocalised π electron system. The most common example is benzene, C₆H₆. Understanding the reactions of arenes is crucial for A-Level Chemistry, as they showcase the unique stability and reactivity of the aromatic ring, primarily undergoing electrophilic substitution rather than typical addition reactions.

芳烃（又称芳香烃）含有一个或多个具有离域π电子体系的苯环。最常见的例子是苯（C₆H₆）。理解芳烃的反应对于A-Level化学至关重要，因为这些反应体现了芳香环独特的稳定性和反应性，主要发生亲电取代而非典型的加成反应。

1. Introduction to Arenes and the Delocalised Model | 芳烃与离域模型介绍

Arenes are hydrocarbons containing one or more benzene rings. Benzene, C₆H₆, has a planar hexagonal ring with delocalised π electrons above and below the plane. This delocalisation gives it exceptional stability, reflected in a lower enthalpy of hydrogenation than expected. The carbon–carbon bonds are all equal in length, intermediate between single and double bonds. Due to this stability, benzene tends to undergo substitution reactions that preserve the delocalised ring, rather than addition reactions that would disrupt it.

芳烃是含有一个或多个苯环的烃。苯（C₆H₆）具有平面六边形环状结构，离域π电子分布在环平面的上下方。这种离域作用使其具有特别的稳定性，表现为氢化焓低于预期值。碳碳键长完全相等，介于单键和双键之间。由于这种稳定性，苯倾向于发生保留离域环的取代反应，而不是破坏离域环的加成反应。

2. Electrophilic Substitution Mechanism | 亲电取代机理

The characteristic reaction of arenes is electrophilic substitution. In this two-step mechanism, an electrophile (E⁺) attacks the π electron cloud, forming a carbocation intermediate (arenium ion or Wheland intermediate) where the positive charge is delocalised over the ring. Then, loss of a proton (H⁺) restores the aromatic system. The overall process substitutes a hydrogen atom with the electrophile. The delocalised intermediate is stabilised by resonance, making this a low-energy pathway.

芳烃的特征反应是亲电取代。在这个两步机理中，亲电试剂 (E⁺) 进攻π电子云，形成一个碳正离子中间体（芳基正离子或Wheland中间体），正电荷在此中间体上离域。随后，失去一个质子（H⁺）恢复芳香体系。总的结果是氢原子被亲电试剂取代。离域中间体通过共振稳定，使其成为低能量路径。

3. Nitration of Benzene | 苯的硝化反应

Benzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid at 50–60 °C to form nitrobenzene. The electrophile is the nitronium ion, NO₂⁺, generated by the reaction: HNO₃ + 2H₂SO₄ ⇌ NO₂⁺ + 2HSO₄⁻ + H₃O⁺. The overall equation: C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O. Sulfuric acid acts as a catalyst and dehydrating agent. Nitrobenzene is a pale yellow liquid used in the manufacture of aniline and dyes.

苯与浓硝酸和浓硫酸的混合物在50–60 °C下反应生成硝基苯。亲电试剂是硝酰正离子 NO₂⁺，通过反应 HNO₃ + 2H₂SO₄ ⇌ NO₂⁺ + 2HSO₄⁻ + H₃O⁺ 生成。总方程式为：C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O。硫酸充当催化剂和脱水剂。硝基苯是一种淡黄色液体，用于制造苯胺和染料。

4. Halogenation of Benzene | 苯的卤化反应

Benzene reacts with chlorine or bromine in the presence of a halogen carrier catalyst (e.g., AlCl₃ or FeBr₃) at room temperature to form chlorobenzene or bromobenzene. The electrophile is a halonium ion (Cl⁺ or Br⁺) formed by polarisation of the halogen by the Lewis acid catalyst. For chlorination: C₆H₆ + Cl₂ → C₆H₅Cl + HCl. The reaction requires anhydrous conditions to prevent catalyst hydrolysis. Halogenobenzenes are important intermediates in organic synthesis.

苯在卤素载体催化剂（如 AlCl₃ 或 FeBr₃）存在下，在室温下与氯或溴反应生成氯苯或溴苯。亲电试剂是由路易斯酸催化剂极化卤素分子而形成的卤正离子（Cl⁺ 或 Br⁺）。氯化反应：C₆H₆ + Cl₂ → C₆H₅Cl + HCl。反应需要在无水条件下进行，以免催化剂水解。卤代苯是有机合成中的重要中间体。

5. Friedel-Crafts Alkylation | Friedel-Crafts 烷基化

Friedel-Crafts alkylation introduces an alkyl group onto the benzene ring. The reaction uses a haloalkane (R–X) and a Lewis acid catalyst (AlCl₃) under anhydrous conditions. The electrophile is a carbocation (R⁺) generated from the haloalkane. Example: C₆H₆ + CH₃CH₂Cl → C₆H₅CH₂CH₃ + HCl. This reaction forms a new C–C bond but can lead to polyalkylation and rearrangements of the carbocation. It is useful for making alkylbenzenes.

Friedel-Crafts 烷基化反应在苯环上引入一个烷基。该反应使用卤代烷（R–X）和路易斯酸催化剂（AlCl₃），在无水条件下进行。亲电试剂是由卤代烷生成的碳正离子（R⁺）。例如：C₆H₆ + CH₃CH₂Cl → C₆H₅CH₂CH₃ + HCl。此反应形成新的 C–C 键，但可能导致多烷基化和碳正离子重排。该反应用于制备烷基苯。

6. Friedel-Crafts Acylation | Friedel-Crafts 酰基化

Friedel-Crafts acylation introduces an acyl group (RCO–) onto the benzene ring. It uses an acyl chloride (RCOCl) and AlCl₃ catalyst. The electrophile is an acylium ion (RCO⁺), which is resonance-stabilised. Example: C₆H₆ + CH₃COCl → C₆H₅COCH₃ + HCl. Ketones are formed. Unlike alkylation, acylation does not suffer from polyacylation or rearrangement. The product ketone can be reduced (e.g., using Zn/Hg, HCl – Clemmensen reduction) to an alkylbenzene, providing a two-step route to pure monoalkylbenzenes.

Friedel-Crafts 酰基化反应在苯环上引入一个酰基（RCO–）。它使用酰氯（RCOCl）和 AlCl₃ 催化剂。亲电试剂是酰基正离子（RCO⁺），该离子通过共振稳定。例如：C₆H₆ + CH₃COCl → C₆H₅COCH₃ + HCl。生成酮。与烷基化不同，酰基化不会发生多酰化和重排。产物酮可进一步还原（例如用 Zn/Hg, HCl —— Clemmensen 还原）为烷基苯，从而提供一条两步合成纯单烷基苯的路线。

7. Sulfonation of Benzene | 苯的磺化反应

Sulfonation introduces a sulfonic acid group (–SO₃H) onto the benzene ring. The reaction uses concentrated sulfuric acid or fuming sulfuric acid (oleum, H₂S₂O₇) at elevated temperatures. The electrophile is sulfur trioxide, SO₃. Equation: C₆H₆ + H₂SO₄ (fuming) ⇌ C₆H₅SO₃H + H₂O. The reaction is reversible; the sulfonic acid group can be removed by heating with dilute acid. Benzenesulfonic acid is used in detergents and dyes.

磺化反应在苯环上引入磺酸基（–SO₃H）。反应使用浓硫酸或发烟硫酸（oleum, H₂S₂O₇）在较高温度下进行。亲电试剂是三氧化硫（SO₃）。方程式：C₆H₆ + H₂SO₄（发烟） ⇌ C

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）