Uses of Halogenoalkanes | 卤代烷的用途

📚 Uses of Halogenoalkanes | 卤代烷的用途

Halogenoalkanes are a family of organic compounds in which one or more hydrogen atoms in an alkane have been replaced by halogen atoms. They have many direct applications, from solvents and refrigerants to anaesthetics and fire-fighting agents, and they are also essential intermediates in organic synthesis.

卤代烷是一类有机化合物，烷烃分子中一个或多个氢原子被卤素原子取代。它们具有许多直接用途，从溶剂、制冷剂到麻醉剂和灭火剂，同时也是有机合成中重要的中间体。

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1. What Are Halogenoalkanes? | 什么是卤代烷？

Halogenoalkanes are alkanes in which one or more hydrogen atoms have been replaced by halogen atoms such as fluorine, chlorine, bromine or iodine. A monohaloalkane has the general formula CnH₂ₙ₊₁X. The carbon-halogen bond is polar because halogens are more electronegative than carbon, and the bond strength decreases down Group 17 from C–F to C–I.

卤代烷是烷烃中一个或多个氢原子被氟、氯、溴或碘等卤素原子取代后形成的化合物。一卤代烷的通式为 CnH₂ₙ₊₁X。由于卤素电负性大于碳，碳-卤键具有极性；从 C–F 到 C–I，键强度沿第 17 族向下逐渐减弱。

This polar bond gives halogenoalkanes their useful solvent properties, while the ability of the halogen to act as a leaving group makes them reactive in nucleophilic substitution and elimination reactions.

这种极性键赋予卤代烷优良的溶剂性能，而卤素作为离去基团的能力又使它们在亲核取代和消除反应中具有反应活性。

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2. Industrial and Laboratory Solvents | 工业与实验室溶剂

Short-chain halogenoalkanes such as dichloromethane (CH₂Cl₂), trichloromethane (CHCl₃) and tetrachloromethane (CCl₄) are excellent solvents for oils, fats, waxes and many covalent organic compounds. Their polar C–X bonds allow dipole–dipole interactions, while the rest of the molecule gives van der Waals interactions with non-polar solutes.

二氯甲烷（CH₂Cl₂）、三氯甲烷（CHCl₃）和四氯化碳（CCl₄）等短链卤代烷是油脂、蜡和许多共价有机化合物的优良溶剂。极性的 C–X 键能形成偶极-偶极作用，分子的其余部分则与非极性溶质产生范德华力。

Halogenoalkane / 卤代烷	Formula / 分子式	Use and hazard / 用途与危害
Dichloromethane / 二氯甲烷	CH₂Cl₂	Paint stripper, extraction solvent; suspected carcinogen / 脱漆剂、萃取溶剂；疑似致癌物
Trichloromethane / 三氯甲烷	CHCl₃	Former anaesthetic, laboratory solvent; hepatotoxic / 曾用作麻醉剂、实验室溶剂；肝毒性
Tetrachloromethane / 四氯化碳	CCl₄	Former solvent and fire extinguisher; toxic to liver and ozone layer / 曾用作溶剂和灭火剂；对肝脏和臭氧层有害

However, tetrachloromethane and trichloromethane are now strictly controlled because of their liver toxicity and carcinogenic potential.

然而，四氯化碳和三氯甲烷因肝毒性和潜在致癌性现已受到严格控制。

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3. Dry Cleaning and Degreasing | 干洗与脱脂

Tetrachloroethylene (Cl₂C=CCl₂), also called perchloroethylene, is widely used in dry cleaning. It dissolves non-polar stains such as grease and oil without swelling or shrinking natural fibres like wool and silk. Trichloroethylene (CHCl=CCl₂) is used as a metal degreaser in engineering workshops.

四氯乙烯（Cl₂C=CCl₂，又称全氯乙烯）广泛用于干洗。它能溶解油脂等非极性污渍，又不会使羊毛、丝绸等天然纤维膨胀或收缩。三氯乙烯（CHCl=CCl₂）在工程车间中用作金属脱脂剂。

Both compounds are non-flammable and volatile, which makes them convenient to use. However, they are toxic and can contaminate groundwater if released, so modern systems must be closed-loop and carefully regulated.

这两种化合物均不易燃且易挥发，因此使用方便。但它们具有毒性，若泄漏会污染地下水，因此现代系统必须采用封闭循环并受到严格监管。

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4. Refrigerants and Coolants | 制冷剂与冷却剂

Chlorofluorocarbons (CFCs) such as CCl₂F₂ (CFC-12) were widely used as refrigerants because they are non-toxic, non-flammable and chemically stable, with suitable boiling points for vapour-compression cooling. In the refrigeration cycle, the liquid refrigerant evaporates inside the cooling coil and absorbs latent heat from the surroundings.

氯氟烃（CFC）如 CCl₂F₂（CFC-12）曾广泛用作制冷剂，因为它们无毒、不易燃、化学性质稳定，并且具有适合蒸汽压缩制冷的沸点。在制冷循环中，液态制冷剂在蒸发盘管内汽化，从周围环境吸收潜热。

Modern replacements include hydrochlorofluorocarbons (HCFCs) such as CHClF₂ (HCFC-22) and hydrofluorocarbons (HFCs) such as CH₂FCF₃ (HFC-134a). HFCs contain no chlorine, so they have zero ozone-depletion potential, although many are still potent greenhouse gases.

现代替代品包括氢氯氟烃（HCFC，如 CHClF₂，即 HCFC-22）和氢氟烃（HFC，如 CH₂FCF₃，即 HFC-134a）。HFC 不含氯，因此臭氧消耗潜值为零，但其中许多仍是强效温室气体。

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5. Aerosol Propellants | 气雾推进剂

Aerosol paints, deodorants, hairsprays and medical inhalers once used CFCs as propellants. A liquefied halogenoalkane is held under pressure in the can; when the valve is opened, it rapidly vaporises and pushes the product out as fine droplets. CFCs were ideal because they give steady pressure and are chemically inert.

喷漆、除臭剂、发胶和药用吸入剂曾使用 CFC 作为推进剂。液化卤代烷在罐内处于压力下；当阀门打开时，它迅速汽化，将内容物以细小液滴形式喷出。CFC 之所以理想，是因为它们能提供稳定压力且化学惰性。

Because CFCs damage the ozone layer, many aerosol products now use HFCs, hydrocarbons such as butane, or compressed gases like nitrogen.

由于 CFC 会破坏臭氧层，许多气雾产品现在使用 HFC、丁烷等烃类或氮气等压缩气体。

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6. Fire Extinguishers | 灭火剂

Bromine-containing halogenoalkanes called halons, such as CBrClF₂ (halon 1211) and CBrF₃ (halon 1301), are excellent fire-extinguishing agents. In a flame, heat breaks the C–Br bond and releases bromine radicals, which intercept reactive H• and OH• radicals in the combustion chain reaction. This stops the flame rapidly.

含溴的卤代烷称为哈龙，例如 CBrClF₂（哈龙 1211）和 CBrF₃（哈龙 1301），是优良的灭火剂。在火焰中，热量使 C–Br 键断裂并释放溴自由基，溴自由基捕获燃烧链反应中的 H• 和 OH• 自由基，从而迅速阻止火焰。

Halons are particularly useful for electrical fires and enclosed spaces because they do not leave a damaging residue. However, bromine is even more destructive to stratospheric ozone than chlorine, so halons are now banned except for critical uses such as aircraft fire protection.

哈龙特别适用于电气火灾和密闭空间，因为它们不会留下破坏性残留物。然而，溴对平流层臭氧的破坏力甚至比氯更强，因此哈龙现已禁止使用，仅保留飞机防火等关键用途。

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7. Anaesthetics | 麻醉剂

Trichloromethane (chloroform, CHCl₃) was one of the earliest general anaesthetics, but its liver and heart toxicity ended its routine use. Halothane (CF₃CHBrCl) became a widely used modern inhalational anaesthetic because it is volatile, relatively non-flammable and gives smooth induction with rapid recovery.

三氯甲烷（氯仿，CHCl₃）是最早的全身麻醉剂之一，但因肝毒性和心脏毒性已不再常规使用。氟烷（CF₃CHBrCl）曾是广泛使用的现代吸入麻醉剂，因为它易挥发、相对不易燃，并且诱导平稳、苏醒迅速。

Other halogenated ethers such as isoflurane and sevoflurane are still important in surgery. The strong C–F bonds in these molecules reduce metabolism and therefore reduce the formation of toxic breakdown products.

异氟烷和七氟烷等其他卤代醚在手术中仍然很重要。这些分子中牢固的 C–F 键可降低代谢，从而减少有毒分解产物的生成。

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8. Pesticides and Soil Fumigants | 农药与土壤熏蒸剂

Volatile halogenoalkanes are used as soil fumigants and pesticides. Methyl bromide (CH₃Br) has broad biocidal activity against nematodes, fungi and weeds, and was widely used before planting strawberries, tomatoes and other high-value crops. Other examples include 1,3-dichloropropene and chloropicrin (CCl₃NO₂).

挥发性卤代烷可用作土壤熏蒸剂和农药。溴甲烷（CH₃Br）对线虫、真菌和杂草具有广谱杀灭作用，在种植草莓、番茄等高价值作物前曾广泛使用。其他例子包括 1,3-二氯丙烯和氯化苦（CCl₃NO₂）。

Many organochlorine pesticides, such as DDT, are very persistent in soil and food chains. They are fat-soluble and undergo bioaccumulation, causing harm to birds, fish and other wildlife.

许多有机氯农药（如 DDT）在土壤和食物链中非常持久。它们易溶于脂肪并发生生物富集，对鸟类、鱼类和其他野生动物造成危害。

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9. Synthetic Intermediates | 合成中间体

In organic synthesis, halogenoalkanes are key intermediates because the carbon-halogen bond undergoes nucleophilic substitution and elimination. For example, bromoethane (CH₃CH₂Br) can be converted into ethanol by heating with aqueous sodium hydroxide, into ethylamine by reaction with excess ammonia, or into propanenitrile by heating with potassium cyanide in ethanol.

在有机合成中，卤代烷是重要的中间体，因为碳-卤键能发生亲核取代和消除反应。例如，溴乙烷（CH₃CH₂Br）与氢氧化钠水溶液加热可转化为乙醇，与过量氨反应可生成乙胺，或在乙醇中与氰化钾加热可生成丙腈。

R–X + OH⁻ → R–OH + X⁻

The nitrile product has one extra carbon atom, so the reaction with cyanide ions is a useful way to extend a carbon chain. Halogenoalkanes can also be converted into alkenes by elimination with hot ethanolic NaOH.

腈类产物多了一个碳原子，因此与氰根离子的反应是增长碳链的常用方法。卤代烷也可以在热的

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