Reactions of Phenol | 酚的化学反应

📚 Reactions of Phenol | 酚的化学反应

Phenol (C₆H₅OH) is an aromatic alcohol in which the -OH group is directly attached to a benzene ring. Its reactions are dominated by the electron-rich aromatic ring and the weakly acidic O-H bond.

苯酚（C₆H₅OH）是一种芳香醇，羟基直接连接在苯环上。其反应主要围绕富电子的芳香环和弱酸性的 O-H 键展开。

1. Structure and Bonding in Phenol | 苯酚的结构与成键

In phenol, a lone pair on the oxygen atom is delocalised into the π system of the benzene ring. This overlap lowers the electron density on oxygen and weakens the O-H bond, making phenol more acidic than typical aliphatic alcohols.

在苯酚中，氧原子上的孤对电子离域到苯环的 π 体系中。这种重叠降低了氧上的电子密度，削弱了 O-H 键，使苯酚比一般脂肪醇更酸。

At the same time, the ring becomes electron-rich at the 2-, 4- and 6- positions, so phenol undergoes electrophilic substitution much faster than benzene.

同时，苯环在 2、4、6 位变得富电子，因此苯酚发生亲电取代反应的速率远快于苯。

2. Acidity of Phenol | 苯酚的酸性

Phenol ionises slightly in water to give the phenoxide ion and H⁺. The phenoxide ion is stabilised by resonance, with the negative charge spread over the oxygen and the benzene ring.

苯酚在水中微弱电离，生成苯氧负离子和 H⁺。苯氧负离子通过共振稳定，负电荷分散到氧原子和苯环上。

C₆H₅OH + H₂O ⇌ C₆H₅O⁻ + H₃O⁺

This is why phenol is a weak acid with pKₐ ≈ 9.9, whereas ethanol has pKₐ ≈ 16 and ethanoic acid has pKₐ ≈ 4.8. Phenol is therefore about 10⁶ times more acidic than ethanol, but about 10⁵ times less acidic than ethanoic acid.

因此苯酚是一种弱酸，pKₐ 约为 9.9；而乙醇的 pKₐ 约为 16，乙酸的 pKₐ 约为 4.8。苯酚的酸性约为乙醇的 10⁶ 倍，但约为乙酸的 10⁻⁵ 倍。

3. Reaction with Sodium Metal | 与金属钠的反应

Phenol reacts with sodium metal to form sodium phenoxide and hydrogen gas, just like alcohols, but the reaction is faster because phenol is more acidic.

苯酚与金属钠反应生成苯氧钠和氢气，与醇类似，但由于苯酚酸性更强，反应更快。

2C₆H₅OH + 2Na → 2C₆H₅ONa + H₂

Sodium phenoxide is an ionic salt containing the C₆H₅O⁻ ion, which is much more stable than an alkoxide ion due to resonance delocalisation.

苯氧钠是一种离子型盐，含有 C₆H₅O⁻ 离子；由于共振离域，该离子比醇氧负离子稳定得多。

4. Reaction with Sodium Hydroxide | 与氢氧化钠的反应

Phenol dissolves in aqueous sodium hydroxide to give a colourless solution of sodium phenoxide. This is an acid-base neutralisation; alcohols do not react with NaOH in aqueous solution.

苯酚溶于氢氧化钠水溶液，生成无色苯氧钠溶液。这是一次酸碱中和反应；醇在水溶液中不与 NaOH 反应。

C₆H₅OH + NaOH → C₆H₅ONa + H₂O

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

更多咨询请联系16621398022（同微信）