📚 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⁺
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
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