📚 Alcohols, Carboxylic Acids and Related Compounds | 醇、羧酸及相关化合物
Alcohols, carboxylic acids and their closely linked derivatives—such as esters, acyl chlorides, aldehydes and ketones—form a central functional group family in A-Level Chemistry. This article systematically explores their structures, nomenclature, physical properties, preparations, characteristic reactions and interconversions. By mastering these concepts, students can confidently handle synthesis, mechanism and analysis questions that regularly appear on Cambridge examination papers.
醇、羧酸以及与之紧密关联的衍生物（如酯、酰氯、醛和酮）构成了A-Level化学中一个核心的官能团家族。本文系统地探讨它们的结构、命名、物理性质、制备方法、特征反应和相互转化。掌握这些概念后，学生能够充满信心地应对剑桥考试中频繁出现的合成、机理和分析类题目。
1. Introduction to Alcohols | 醇类简介
Alcohols are organic compounds containing at least one hydroxyl group (–OH) bonded to a saturated carbon atom. The general formula for a saturated monohydric alcohol is CₙH₂ₙ₊₁OH. The –OH group is the functional group that dictates the chemical behaviour of the molecule, exhibiting polar O–H and C–O bonds which allow hydrogen bonding and nucleophilic reactions.
醇是至少含有一个与饱和碳原子相连的羟基（–OH）的有机化合物。饱和一元醇的通式为 CₙH₂ₙ₊₁OH。羟基是决定分子化学行为的官能团，它具有极性的 O–H 键和 C–O 键，能够形成氢键并参与亲核反应。
Methanol (CH₃OH), ethanol (CH₃CH₂OH) and propan-1-ol are common examples. Depending on the number of alkyl groups attached to the carbon bearing the –OH, alcohols are classified as primary (1°), secondary (2°) or tertiary (3°), a distinction that profoundly influences their oxidation behaviour and reactivity.
甲醇（CH₃OH）、乙醇（CH₃CH₂OH）和正丙醇是常见的例子。根据与带羟基的碳原子相连的烷基数目，醇可分为伯醇（1°）、仲醇（2°）或叔醇（3°），这一区别深刻影响着它们的氧化行为和反应活性。
2. Classification and Nomenclature of Alcohols | 醇的分类与命名
In IUPAC nomenclature, the longest continuous carbon chain containing the –OH group is selected, and the ‘-e’ ending of the corresponding alkane is replaced by ‘-ol’. The chain is numbered so that the hydroxyl carbon receives the lowest possible number. Substituents are cited as prefixes with their own locants.
在 IUPAC 命名法中，选择含 –OH 的最长连续碳链作为主链，将相应烷烃词尾的“-e”替换为“-ol”。主链编号应使带有羟基的碳位次最小。取代基则作为前缀并标出其位置编号。
Examples include:- CH₃CH₂CH₂OH – propan-1-ol
- CH₃CH(OH)CH₃ – propan-2-ol
- (CH₃)₃COH – 2-methylpropan-2-ol
例子包括：
- CH₃CH₂CH₂OH – 丙-1-醇
- CH₃CH(OH)CH₃ – 丙-2-醇
- (CH₃)₃COH – 2-甲基丙-2-醇
When alcohols contain more than one –OH group, they are named as diols, triols, etc., and the ending ‘-ol’ is retained with appropriate multipliers. The classification as primary, secondary or tertiary remains vital for predicting the outcomes of oxidation and dehydration.
当醇含有不止一个 –OH 时，它们被命名为二醇、三醇等，词尾仍为“-ol”并加上适当的倍数词头。伯、仲、叔醇的分类对于预测氧化和脱水反应的结果仍然至关重要。
3. Physical Properties of Alcohols | 醇的物理性质
Due to the highly electronegative oxygen atom, the O–H bond is polar, and alcohols can form intermolecular hydrogen bonds. This results in significantly higher boiling points compared to alkanes or ethers of similar molar mass. For example, ethanol (boiling point 78 °C) boils much higher than propane (–42 °C) and dimethyl ether (–24 °C).
由于氧原子的电负性很高，O–H 键具有极性，醇分子间能够形成氢键。这使得它们的沸点远高于相对分子质量相近的烷烃或醚。例如，乙醇的沸点为 78 °C，远高于丙烷（–42 °C）和二甲醚（–24 °C）。
Short-chain alcohols (C₁–C₃) are completely miscible with water because the hydroxyl group can form hydrogen bonds with water molecules. As the hydrocarbon chain lengthens, solubility decreases because the hydrophobic alkyl part dominates. The ability to form hydrogen bonds also affects viscosity and surface tension.
短链醇（C₁–C₃）与水完全混溶，因为羟基能与水分子形成氢键。随着碳链增长，疏水的烷基部分逐渐主导，溶解度随之降低。形成氢键的能力也会影响黏度和表面张力。
4. Preparation of Alcohols | 醇的制备
+ H₂O → CH₃CH₂OH. Typical conditions are 300 °C and 60 atm. This method produces high-purity ethanol and is continuous.
工业上制备乙醇的主要途径是乙烯的直接水合法，使用蒸气及负载于固体载体上的磷酸(V) 催化剂：CH₂=CH₂ + H₂O → CH₃CH₂OH。典型条件为 300 °C 和 60 atm。该方法可连续生产出高纯度的乙醇。
+ 2CO₂. This occurs optimally around 37 °C under anaerobic conditions. The ethanol concentration reaches about 10–15% before yeast activity ceases, and the product is purified by fractional distillation.
利用酵母菌中的酶对糖类（如葡萄糖）进行发酵提供了另一条途径：C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂。该反应在约 37 °C 的厌氧条件下进行。乙醇浓度达到 10–15% 左右时酵母停止活动，产物需通过分馏纯化。
Alcohols can also be prepared in the laboratory by nucleophilic substitution of halogenoalkanes using aqueous sodium hydroxide, and by reduction of aldehydes, ketones or carboxylic acids using LiAlH₄.
在实验室中，还可以通过卤代烷与氢氧化钠溶液的亲核取代反应，以及用 LiAlH₄ 还原醛、酮或羧酸来制备醇。
5. Reactions of Alcohols: Oxidation | 醇的氧化反应
Oxidising agents such as acidified potassium dichromate(VI) (K₂Cr₂O₇/H₂SO₄) convert alcohols to carbonyl or carboxyl compounds. Primary alcohols are first oxidised to aldehydes and then to carboxylic acids; secondary alcohols yield ketones; tertiary alcohols resist oxidation because they lack a hydrogen atom on the carbon bearing the –OH.
酸化重铬酸钾(VI)（K₂Cr₂O₇/H₂SO₄）等氧化剂可将醇转化为羰基或羧基化合物。伯醇先被氧化成醛，再被氧化成羧酸；仲醇生成酮；叔醇由于带有 –OH 的碳原子上缺少氢原子，不易被氧化。
CH₃CH₂OH + [O] → CH₃CHO + H₂O (distil off the aldehyde)
CH₃CHO + [O] → CH₃COOH (heat under reflux)
CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H₂O
The orange dichromate(VI) ion is reduced to green chromium(III) ion, providing a visible colour change. To obtain the aldehyde from a primary alcohol, the aldehyde must be distilled out as it forms, preventing further oxidation. Full oxidation to the carboxylic acid is achieved by heating under reflux with excess oxidising agent.
橙色的重铬酸根(VI)离子被还原为绿色的铬(III)离子，出现明显的颜色变化。要从伯醇获得醛，必须在醛生成时及时将它蒸馏出来，以避免进一步氧化。通过与过量氧化剂一起加热回流，可实现完全氧化成羧酸。
6. Reactions of Alcohols: Esterification | 醇的酯化反应
Alcohols react with carboxylic acids in the presence of a strong acid catalyst (usually concentrated H₂SO₄) to form esters and water. This reversible condensation reaction reaches equilibrium and is driven forward by using an excess of one reactant and/or removing water.
醇在强酸催化剂（通常为浓硫酸）的存在下与羧酸反应，生成酯和水。这是一个可逆的缩合反应，达到平衡后可通过过量使用某一种反应物和/或移除水来促使反应正向进行。
RCOOH + R'OH ⇌ RCOOR' + H₂O
For example, ethanoic acid reacts with ethanol to give ethyl ethanoate, a sweet-smelling liquid used as a solvent and in flavourings. In nomenclature, the alcohol part becomes an alkyl group and the acid part ends in ‘-oate’.
例如，乙酸与乙醇反应生成乙酸乙酯，这是一种具有甜香气味的液体，用作溶剂和调味品。在命名中，由醇提供的那部分成为烷基，由酸提供的那部分词尾为“-oate”（某酸酯）。
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
Esterification is not only a characteristic test for both functional groups but also a key technique in organic synthesis, linking alcohols to carboxylic acid derivatives.
酯化反应不仅仅是这两种官能团的特征检验反应，也是有机合成中连接醇与羧酸衍生物的一项关键技术。
7. Dehydration of Alcohols | 醇的脱水反应
When heated with an acid catalyst, alcohols undergo elimination to form alkenes. Ethanol, for instance, dehydrates to ethene when passed over hot aluminium oxide (Al₂O₃) at 350 °C or heated with concentrated sulfuric acid at 170 °C.
在酸催化剂作用下加热，醇会发生消除反应生成烯烃。例如，乙醇在 350 °C 下通过热的氧化铝（Al₂O₃）或在 170 °C 下与浓硫酸一同加热时，就会脱水生成乙烯。
CH₃CH₂OH → CH₂=CH₂ + H₂O
The mechanism proceeds via protonation of the hydroxyl group, loss of water to form a carbocation, and subsequent loss of a proton to give the alkene. For unsymmetrical alcohols, the major product follows Zaitsev’s rule, favouring the more substituted, stable alkene.
该反应机理为：羟基先被质子化，然后失去一分子水形成碳正离子，接着失去一个质子得到烯烃。对于不对称醇，主产物遵循扎伊采夫规则，偏向生成取代较多、更稳定的烯烃。
At lower temperatures and with an excess of alcohol, intermolecular dehydration can occur to form ethers, but alkene formation is thermodynamically preferred under the vigorous conditions described.
在较低温度和醇过量时，可能发生分子间脱水生成醚，但在上述激烈条件下，热力学上更有利于生成烯烃。
8. Introduction to Carboxylic Acids | 羧酸简介
Carboxylic acids contain the carboxyl functional group –COOH, which is a combination of a carbonyl (C=O) and a hydroxyl (– or saturated monocarboxylic acids is CₙH₂ₙ₊₁COOH. They are named by replacing the terminal ‘-e’ of the parent alkane with ‘-oic acid’, e.g., methanoic acid (HCOOH), ethanoic acid (CH₃COOH).
羧酸含有羧基官能团 –COOH，它是羰基（C＝O）和羟基（–OH）的组合体。饱和一元羧酸的通式为 CₙH₂ₙ₊₁COOH。命名时将母体烷烃词尾的“-e”替换为“-oic acid”（某酸），如甲酸（HCOOH）、乙酸（CH₃COOH）。
The carboxyl group is highly polar, and carboxylic acids form strong intermolecular hydrogen bonds, often existing as dimers even in the vapour phase. Consequently, they have significantly elevated boiling points relative to alcohols of comparable molar mass. Ethanoic acid boils at 118 °C, while propan-1-ol boils at 97 °C.
羧基极性很强，羧酸分子间能形成牢固的氢键，即便在蒸气相中也常以二聚体形式存在。因此，它们的沸点远高于相对分子质量相近的醇。乙酸的沸点为 118 °C，而丙-1-醇的沸点为 97 °C。
The acidity arises from resonance stabilisation of the carboxylate anion, which delocalises the negative charge equally over two oxygen atoms, making the O–H proton more readily donated than in alcohols.
羧酸的酸性来源于羧酸根阴离子的共振稳定作用，它将负电荷均匀地离域在两个氧原子上，使得 O–H 上的质子比醇更容易离去。
9. Acidity and Reactions of Carboxylic Acids | 羧酸的酸性与反应
Carboxylic acids are weak acids, partially dissociating in water with pKₐ values typically around 4–5. They react with reactive metals, bases and carbonates to form carboxylate salts. For instance, ethanoic acid reacts with sodium carbonate to release carbon dioxide gas, a classic test.
羧酸是弱酸，在水中部分电离，其 pKₐ 值通常在 4–5 左右。它们能与活泼金属、碱以及碳酸盐反应，生成羧酸盐。例如，乙酸与碳酸钠反应会释放出二氧化碳气体，这是一个经典的检验方法。
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
CH₃COOH + NaOH → CH₃COONa + H₂O
Carboxylic acids can be reduced by strong reducing agents such as lithium aluminium hydride (LiAlH₄) to primary alcohols, though this requires anhydrous conditions. They also undergo nucleophilic acyl substitution to give a host of derivatives like esters, acyl chlorides and amides.
羧酸可被强还原剂如氢化铝锂（LiAlH₄）还原成伯醇，但需在无水条件下进行。它们还能发生亲核酰基取代反应，生成诸如酯、酰氯和酰胺等一系列衍生物。
10. Esters: Formation and Hydrolysis | 酯的形成与水解
As described in Section 6, esters are produced by the condensation of a carboxylic acid and an alcohol. They can undergo hydrolysis—the reverse of esterification—catalysed by either acid or base. Acid hydrolysis regenerates the carboxylic acid and alcohol in an equilibrium process.
如第6节所述，酯由羧酸与醇缩合生成。它们可以发生水解——即酯化的逆过程——可被酸或碱催化。酸性水解是一个平衡过程，重新生成羧酸和醇。
CH₃COOCH₂CH₃ + H₂O ⇌ CH₃COOH + CH₃CH₂OH (H⁺, heat)
Base-catalysed hydrolysis, often called saponification, uses aqueous sodium hydroxide and goes to completion because the carboxylic acid is deprotonated to form the carboxylate salt, which does not re-esterify. The final products are the salt of the acid and the alcohol.
碱催化水解通常称为皂化反应，使用氢氧化钠水溶液，反应可进行完全，因为生成的羧酸会被去质子化形成羧酸盐，而羧酸盐不会再发生酯化。最终产物为酸的盐和醇。
CH₃COOCH₂CH₃ + NaOH → CH₃COONa + CH₃CH₂OH
Esters are widely used in perfumes, solvents and plasticisers, and their formation and cleavage are fundamental to organic synthesis and biochemistry.
酯广泛用于香料、溶剂和增塑剂中，它们的生成与裂解反应是有机合成和生物化学的基础。
11. Acyl Chlorides and Related Reactions | 酰氯及相关反应
Acyl chlorides (or acid chlorides) are highly reactive carboxylic acid derivatives where the –OH group has been replaced by a chlorine atom. They are typically prepared by reacting a carboxylic acid with thionyl chloride (SOCl₂) or phosphorus(V) chloride (PCl₅).
酰氯（或称酸性氯化物）是一类高活性的羧酸衍生物，其中的 –OH 基团被氯原子取代。它们通常通过羧酸与亚硫酰氯（SOCl₂）或五氯化磷（PCl₅）反应制备。
CH₃COOH + SOCl₂ → CH₃COCl + SO₂ + HCl
Acyl chlorides react vigorously with nucleophiles. With water, they hydrolyse rapidly to form the parent carboxylic acid and HCl fumes. With alcohols, they produce esters without the need for an acid catalyst and at a much faster rate than direct esterification. The reaction with ammonia or amines yields amides.
酰氯与亲核试剂会发生剧烈反应。它们遇水迅速水解生成母体羧酸和氯化氢烟雾；与醇反应生成酯，无需酸催化剂且比直接酯化快得多；与氨或胺反应则生成酰胺。
CH₃COCl + C₂H₅OH → CH₃COOC₂H₅ + HCl
CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl
The high reactivity of acyl chlorides makes them useful intermediates for introducing acyl groups into other molecules, linking the chemistry of alcohols and carboxylic acids to a broader framework of functional group interconversions.
酰氯的高活性使它们成为向其他分子引入酰基的实用中间体，将醇和羧酸的化学与更广泛的官能团相互转化网络联系起来。
12. Summary and Interconversion Pathways | 总结与转化路径
Alcohols, aldehydes/ketones, carboxylic acids, esters and acyl chlorides form an interconnected family whose chemistry revolves around oxidation level and nucleophilic acyl substitution. Primary alcohols can be oxidised to aldehydes and then to carboxylic acids; secondary alcohols give ketones. Carboxylic acids are reduced back to primary alcohols or converted into esters and acyl chlorides. Esters can be hydrolysed to regenerate the parent acid and alcohol, while acyl chlorides provide a fast and complete route to esters and amides.
醇、醛/酮、羧酸、酯和酰氯构成了一个相互关联的家族，其化学性质围绕着氧化水平和亲核酰基取代而展开。伯醇可氧化为醛，进而氧化为羧酸；仲醇生成酮。羧酸可被还原回伯醇，或转化为酯和酰氯。酯可水解再生母体酸和醇，而酰氯则提供了通向酯和酰胺的快速且完全的途径。
Mastering these relationships, together with practical aspects like distillation under reflux, use of drying agents and the characteristic colour changes of oxidising agents, is essential for success in Cambridge A-Level Chemistry. The ability to predict products, design synthetic routes and explain observations demonstrates deep understanding of this vital topic.
掌握这些关系，并结合回流蒸馏、干燥剂使用以及氧化剂的特征颜色变化等实验操作，对于在剑桥 A-Level 化学考试中取得成功至关重要。能够预测产物、设计合成路线并解释实验现象，充分展现了对这一重要主题的深入理解。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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