# 醇类

> 爱德思国际GCSE化学 · 4CH1 2017
> 来源: https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-alcohols/

本指南覆盖爱德思IGCSE化学（4CH1）2C卷中醇类的全部内容，包括官能团识别、结构绘制、乙醇氧化路径及制备方法。

**先修:** [烯烃官能团与结构绘制的相关知识](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-alkenes/); [基础氧化还原反应的相关理解](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s3-redox-reactions/)

## 学习目标

- 识别醇类中的-OH羟基官能团
- 绘制甲醇、乙醇、丙-1-醇和丁-1-醇的结构式与展开式
- 描述乙醇的三种氧化路径
- 熟记两种乙醇制备方法的精确反应条件
- 解释发酵过程需要隔绝空气与最适温度的原因

## 醇类官能团与命名规则

**醇** — 通式为$C_nH_{2n+1}OH$的有机化合物同系物系列，特征是烷基链上连接有羟基（-OH）官能团。

根据本考纲要求，你仅需熟记直链1-醇异构体，即-OH基团连接在烷基链末端碳原子上的醇。答题时你可以使用未限定位置的名称“丙醇”和“丁醇”来代替丙-1-醇和丁-1-醇。

**例题:** 绘制丁-1-醇的展开结构式，写出它的分子式，并说明可使用的简写名称。

1. 1. 画出由4个碳原子通过单共价键连接的直链，因为“丁烷（butan-）”代表4个碳原子。
2. 2. 按照-1-醇后缀的要求，将-OH官能团连接在第一个（末端）碳原子上。
3. 3. 用氢原子填充每个碳原子上剩余的所有成键空位，确保每个碳原子总共有4个共价键。
4. $$C_4H_9OH$$
5. 4. 可接受的简写名称：丁醇。

**概念自测**

1. What is the defining functional group of alcohols?

   - -COOH
   - -OH
   - -C=C-
   - -COO-

   *解析:* The hydroxyl (-OH) group is the unique functional group for all alcohols.

2. What is the molecular formula of methanol?

   - $CH_3OH$
   - $C_2H_5OH$
   - $C_3H_7OH$
   - $C_4H_9OH$

   *解析:* Methanol has 1 carbon atom, following the $C_nH_{2n+1}OH$ general formula.

*计算器:* allowed

## 乙醇的氧化反应

乙醇有三种你必须为考试熟记的关键氧化反应。所有反应（除不完全燃烧外）的最终产物都是乙酸。

- Complete combustion (burning) in air/oxygen to form carbon dioxide and water
- Microbial oxidation by oxygen in air to form ethanoic acid (vinegar)
- Heating with acidified potassium dichromate(VI) to form ethanoic acid

**例题:** 描述乙醇与稀硫酸、重铬酸钾(VI)共热时发生的可见变化与生成的产物。

1. 1. 确定氧化剂：酸化重铬酸钾(VI)在反应过程中被还原。
2. 2. 可见变化：橙色的重铬酸根离子（$Cr_2O_7^{2-}$）转变为绿色的三价铬离子（$Cr^{3+}$）。
3. 3. 氧化产物：乙醇被完全氧化为乙酸，属于羧酸类。

> **tip**
>
> 与烷烃和烯烃类似，任意醇的完全燃烧都只会生成二氧化碳和水。

> **考试提示:** 答题时务必指明重铬酸钾(VI)是用稀硫酸酸化的，才能拿到全部分数。

## 乙醇制备：乙烯的水合反应

**乙烯水合反应** — 工业上的连续加成反应，乙烯与水蒸气在高温、高压和催化剂作用下反应生成纯乙醇。

你必须熟记该反应的精确条件：磷酸催化剂、约300°C的温度、60–70标准大气压。该工艺使用来源于原油裂解的不可再生乙烯作为原料。

**例题:** 写出乙烯水合生成乙醇的配平符号方程式，并说明该方法相比发酵法的一个优势。

1. 1. 写出反应物分子式：乙烯 = $C_2H_4$，水蒸气 = $H_2O$
2. 2. 写出产物分子式：乙醇 = $C_2H_5OH$
3. $$C_2H_4 + H_2O \rightarrow C_2H_5OH$$
4. 3. 优势：该工艺是快速的连续生产过程，生成的乙醇纯度极高，且无废弃物产生。

## 乙醇制备：葡萄糖的发酵

**发酵** — 植物来源的葡萄糖在酵母酶的作用下分解为乙醇和二氧化碳的厌氧分批反应。

发酵的所需条件：最适温度约为30 °C，隔绝空气（厌氧条件），酵母酶作为生物催化剂。该工艺使用甘蔗、玉米等农作物产出的可再生葡萄糖作为原料。

**例题:** 解释为什么发酵要在隔绝空气、约30 °C的条件下进行，而非100 °C。

1. 1. 隔绝空气：空气中的氧气会使乙醇发生微生物氧化，生成不需要的乙酸（食醋），破坏产物。
2. 2. 约30 °C是酵母酶的最适温度：温度过低会减慢反应速率，而温度高于约40 °C（例如100 °C）时酶会变性，无法再催化反应。

## 乙醇制备方法的对比

| Feature | Hydration of Ethene | Fermentation of Glucose |
| --- | --- | --- |
| Raw material | Ethene (crude oil, non-renewable) | Glucose (crops, renewable) |
| Process type | Continuous 24/7 operation | Batch (stopped when product forms) |
| Conditions | ~300 °C, 60-70 atm, $H_3PO_4$ catalyst | ~30 °C, 1 atm, no air, yeast |
| Product purity | Very pure ethanol | Dilute ethanol (requires distillation) |
| Reaction rate | Fast | Slow (takes days) |

**概念自测**

1. Which method produces a renewable ethanol product?

   - Hydration of ethene
   - Fermentation
   - Both
   - Neither

   *解析:* Fermentation uses glucose from regrowable crops, making it a renewable process.

2. What catalyst is used for ethene hydration?

   - Yeast
   - Iron
   - Phosphoric acid
   - Nickel

   *解析:* Phosphoric acid is the required catalyst for the industrial hydration reaction.

## 常见错误

- **错误做法:** Drawing the -OH group bonded to hydrogen instead of a carbon atom in the alkyl chain
  - 原因: The hydroxyl group is covalently attached to the carbon chain, not a free ion, so this structure is chemically incorrect.
  - 正确做法: Always attach the oxygen atom of the -OH group directly to a carbon atom in the alkyl chain.
- **错误做法:** Stating potassium dichromate(VI) oxidises ethanol without mentioning it is acidified with dilute sulfuric acid
  - 原因: Potassium dichromate only acts as an oxidising agent in acidic conditions, so this missing detail costs you marks.
  - 正确做法: Always refer to 'acidified potassium dichromate(VI)' or explicitly mention the dilute sulfuric acid.
- **错误做法:** Stating fermentation is done at 100 °C to speed up the reaction
  - 原因: Temperatures above ~40 °C denature yeast enzymes, stopping the reaction entirely.
  - 正确做法: Recall fermentation uses an optimum temperature of ~30 °C to maximise enzyme activity without denaturing.
- **错误做法:** Forgetting to specify that fermentation must be carried out in the absence of air
  - 原因: Oxygen in air oxidises ethanol to unwanted ethanoic acid, ruining the desired product.
  - 正确做法: Always state fermentation uses anaerobic (no air) conditions.
- **错误做法:** Drawing the -OH group on the second carbon for propanol or butanol
  - 原因: Only propan-1-ol and butan-1-ol are required for this specification; 2-ol isomers are out of scope.
  - 正确做法: Attach the -OH group to the first (end) carbon in the chain for propanol and butanol.

## 速查表

| Concept | Key Recall Point |
| --- | --- |
| Functional group | -OH (hydroxyl) |
| Methanol formula | $CH_3OH$ |
| Ethanol formula | $C_2H_5OH$ |
| Propanol formula | $C_3H_7OH$ |
| Butanol formula | $C_4H_9OH$ |
| Ethanol combustion products | $CO_2 + H_2O$ |
| Ethanol oxidation product | Ethanoic acid |
| Dichromate colour change | Orange → Green |
| Hydration conditions | ~300°C, 60-70 atm, $H_3PO_4$ catalyst |
| Fermentation conditions | ~30°C, no air, yeast catalyst |
| Fermentation no air reason | Prevents ethanol → ethanoic acid |
| Fermentation temp reason | Max enzyme activity, no denaturing |

## 下一步

Now you have mastered alcohol content for Edexcel IGCSE Chemistry, move on to related organic chemistry topics that build directly on this knowledge. First, study carboxylic acids, the product of ethanol oxidation, including their functional group, structure and reactions. Next, learn about esters, which form when alcohols react with carboxylic acids, another high-frequency Paper 2C topic. You can also revisit alkenes to reinforce your understanding of the hydration reaction raw material, or practice organic synthesis questions that combine multiple functional group reactions to prepare for longer 4-6 mark exam questions.

- [Alkenes](https://www.owlsprep.com/zh/study/edexcel-igcse-chemistry-s4-alkenes/)

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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-alcohols/