# 酯类

> Edexcel 国际普通中等教育证书（IGCSE）化学 · 4CH1 2017年考纲
> 来源: https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-esters/

本指南覆盖Edexcel IGCSE 4CH1卷2C要求的所有酯类相关内容，包括官能团识别、命名、分子式书写、制备与常见用途。

**先修:** [醇的结构、命名与性质](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-alcohols/); [羧酸的结构、命名与性质](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-carboxylic-acids/)

## 学习目标

- 能够在结构式与展开式中识别-COO-酯官能团
- 牢记乙酸乙酯由乙醇与乙酸在浓硫酸催化下反应生成
- 能够书写乙酸乙酯的结构式与展开式
- 能够从母体醇和羧酸推导酯的名称与分子式，反之亦然
- 牢记酯的性质及其在食品香精与香水中的用途
- 能够描述制备乙酸乙酯样品的实验操作方法

## 酯的结构与官能团

**酯键** — 定义所有酯类的共价官能团，由羧酸与醇反应生成

*记法:* -COO-

*例:* In ethyl ethanoate, the ester linkage connects the ethyl group from ethanol to the ethanoate group from ethanoic acid

所有酯都符合通式RCOOR'，其中R是来自母体羧酸的烷基（或氢原子），R'是来自母体醇的烷基。展开式必须明确显示所有化学键，包括酯键中的C=O双键与C-O单键。

**例题:** 画出酯官能团的展开式，标出用于连接烷基的未成键位点。

1. 画出中心碳原子，与一个氧原子形成双键
2. 从同一个碳原子出发，以单键连接第二个氧原子
3. 标出两个未成键位点：一个在中心碳原子上（连接来自酸的烷基），另一个在单键连接的氧原子上（连接来自醇的烷基）

**概念自测**

1. Which functional group is present in all esters?

   - A -OH
   - B -COOH
   - C -COO-
   - D -C=C-

   *解析:* A is the alcohol functional group, B is the carboxylic acid functional group, D is the alkene functional group.

## 酯的命名与分子式书写

无论母体反应物的大小如何，酯的命名都遵循固定的两部分规则。考试要求你能够从给定反应物推导酯的名称，也能从给定酯的名称识别对应的母体反应物。

**例题:** 写出甲醇与丙酸反应生成的酯的名称，并写出其结构式。

1. 从母体醇中提取烷基：甲醇 → 甲基
2. 将母体羧酸的-oic acid后缀替换为-oate：丙酸 → 丙酸酯
3. 将两部分组合得到酯的名称：丙酸甲酯
4. 写出结构式：CH₃CH₂COOCH₃

**例题:** 确定生成乙酸丁酯所使用的母体醇与羧酸。

1. 酯名称的第一部分（丁基）来自醇：丁醇
2. 酯名称的第二部分（乙酸酯基）来自羧酸：乙酸

> **考试提示:** 酯的命名顺序与反应物顺序相反：来自醇的基团放在前面，后面接来自酸的-oate（酸酯）后缀。

## 乙酸乙酯的生成

乙酸乙酯是考试中最常考察的酯类，由乙醇与乙酸在浓硫酸催化下发生可逆缩合反应生成，反应同时生成一分子水作为副产物。

$$CH_3COOH + C_2H_5OH \rightarrow CH_3COOC_2H_5 + H_2O$$

**例题:** 写出乙酸乙酯生成反应的完整配平符号方程式，注明催化剂。

1. 写出反应物的分子式：乙酸（CH₃COOH）和乙醇（C₂H₅OH）
2. 写出产物的化学式：乙酸乙酯（CH₃COOC₂H₅）和水（H₂O）
3. 验证原子守恒：方程式两侧均含有4个C原子、10个H原子和3个O原子
4. 在反应箭头上方标注浓H₂SO₄以表示催化剂

> **tip**
>
> 酯化反应方程式中绝对不能省略水，否则在配平方程式类题目中会被扣分。

## 酯的性质与用途

酯具有两项核心物理性质，这两项性质决定了它们的商业用途：它们挥发性极强（室温下极易蒸发），且带有独特的香甜水果气味。

- **Food flavourings**: Used to replicate the taste and smell of fruits like strawberry, banana, and pineapple in processed foods, confectionery and drinks
- **Perfumes**: Their volatility means fragrant ester molecules travel easily through air to reach the nose, making them ideal for scented products

**例题:** 解释为什么酯可用于香水生产。

1. 酯带有独特宜人的水果香气，正是香水产品所需要的气味
2. 酯具有挥发性，因此带香气的分子极易蒸发，使用者和周边的人都能闻到气味

## 乙酸乙酯的实验室制备实操

你需要熟记中学实验室制备少量乙酸乙酯的简易方法，包括核心的安全注意事项。

1. Add equal volumes of ethanol and ethanoic acid to a boiling tube
2. Add 3-4 drops of concentrated sulfuric acid catalyst to the mixture
3. Warm the tube gently in a 60°C hot water bath for 5 minutes (avoid open flames, as ethanol is flammable)
4. Pour the resulting mixture into a beaker of cold sodium carbonate solution to neutralise unreacted acid and remove impurities
5. An insoluble, sweet-smelling oily layer of ethyl ethanoate will form on the surface of the solution

**例题:** 写出该实验的一项安全注意事项，并说明其必要性。

1. 使用热水浴加热，禁止直接用本生灯明火加热
2. 乙醇属于高度易燃物，明火可能引燃反应混合物

*计算器:* forbidden

## 常见错误

- **错误做法:** Naming esters in the same order as reactants (e.g. ethanol + ethanoic acid → ethanoic ethyl ester)
  - 原因: Ester names reverse the order of parent reactants, with the alcohol-derived group first.
  - 正确做法: Name the alcohol alkyl group first, followed by the acid-derived -oate suffix.
- **错误做法:** Drawing the ester linkage with incorrect bonding, e.g. -CO-OH or -O-CO- with missing double bond
  - 原因: The ester functional group is explicitly -COO- with a C=O double bond adjacent to a C-O single bond.
  - 正确做法: Show all bonds in displayed formulae, including the C=O double bond in the ester linkage.
- **错误做法:** Omitting water as a product in esterification balanced equations
  - 原因: Esterification is a condensation reaction that eliminates one molecule of water per ester molecule formed.
  - 正确做法: Always include H₂O as a product when writing esterification equations.
- **错误做法:** Stating dilute sulfuric acid is used as the esterification catalyst
  - 原因: Only concentrated sulfuric acid acts as an effective catalyst, and also absorbs water to shift equilibrium towards ester products.
  - 正确做法: Explicitly state 'concentrated sulfuric acid' when naming the catalyst.
- **错误做法:** Confusing ester uses with carboxylic acid uses (e.g. stating esters are used as cleaning agents)
  - 原因: Esters have sweet smells and volatility, while carboxylic acids have acidic cleaning properties.
  - 正确做法: Only recall the two specified uses: food flavourings and perfumes.

## 速查表

| Concept | Key Exam Fact |
| --- | --- |
| Ester functional group | -COO- (ester linkage) |
| Ester naming rule | Alkyl (alcohol) + -oate (carboxylic acid) |
| Ethyl ethanoate reactants | Ethanol + ethanoic acid |
| Esterification catalyst | Concentrated sulfuric acid |
| Key ester properties | Volatile, sweet/fruity smell |
| Ester uses | Food flavourings, perfumes |
| Practical test for ester | Sweet oily layer on sodium carbonate solution |

## 下一步

Now you have mastered ester content for Edexcel IGCSE 4CH1 Paper 2C, you are ready to progress to related organic chemistry sub-topics. Esters are a core building block for understanding condensation polymerisation, where ester linkages connect monomer units to form polyesters, a common synthetic material. You should also consolidate your knowledge of alcohols and carboxylic acids, as exam questions frequently combine content from these three sub-topics in longer structured responses. Be sure to practice writing displayed formulae for esters and balanced esterification equations, as these are common high-mark questions on Paper 2C.

- [Alcohols (S4_T05)](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-alcohols/)
- [Carboxylic Acids (S4_T06)](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-carboxylic-acids/)

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来自 [OwlsPrep](https://www.owlsprep.com) —— A-Level / IB / AP / IGCSE 免费学习指南，依据官方考纲编写。原页面：https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-esters/