定义Definition
乙炔是分子式为 C₂H₂ 的最简单炔烃，含碳碳三键，分子呈直线形。它是无色可燃气体，在氧气中燃烧的火焰温度可达约 3300 °C，用于金属焊接和切割，也是传统的有机合成原料。
Acetylene, C₂H₂, is the simplest alkyne, with a carbon–carbon triple bond and a linear molecule. It is a colourless flammable gas whose oxy-acetylene flame reaches about 3300 °C, used for welding and cutting metals, and it is a traditional feedstock for organic synthesis.
结构与成键Structure and bonding
碳原子 sp 杂化，C≡C 由一个 σ 键和两个互相垂直的 π 键组成，键长 120.3 pm，H–C≡C 键角 180°。sp 杂化轨道 s 成分高达 50%，使 C–H 键的氢具有弱酸性（pKa ≈ 25），能被 NaNH₂ 或银氨、铜氨溶液取代生成炔化物。
Carbon is sp hybridised; the C≡C bond consists of one σ bond and two mutually perpendicular π bonds, 120.3 pm long, with an H–C≡C angle of 180°. The 50% s character of the sp hybrid makes the C–H hydrogen weakly acidic (pKa ≈ 25), so it can be replaced using NaNH₂ or ammoniacal silver or copper solutions to give acetylides.
发现与制备Discovery and preparation
1836 年埃德蒙·戴维首次制得乙炔，1860 年贝特洛将其命名为 acétylène。1892 年威尔森在电炉中意外得到碳化钙（电石），使电石加水制乙炔成为廉价方法：CaC₂ + 2 H₂O → C₂H₂↑ + Ca(OH)₂。现代也由天然气部分氧化或烃类裂解生产。
Edmund Davy first made acetylene in 1836, and Berthelot named it acétylène in 1860. In 1892 Willson accidentally produced calcium carbide in an electric furnace, making carbide-and-water a cheap route: CaC₂ + 2 H₂O → C₂H₂↑ + Ca(OH)₂. It is also produced today by partial oxidation of natural gas and by hydrocarbon cracking.
用途与安全Uses and safety
乙炔用于氧炔焰焊接切割，以及合成氯乙烯、乙醛、乙酸乙烯酯和 1,4-丁二醇（雷佩化学）。纯乙炔加压到 0.2 MPa 以上可能分解爆炸，所以钢瓶中把它溶于浸在多孔填料里的丙酮或 DMF 中储存。
Acetylene is used in oxy-acetylene welding and cutting and to make vinyl chloride, acetaldehyde, vinyl acetate and 1,4-butanediol (Reppe chemistry). Pure acetylene above about 0.2 MPa can decompose explosively, so cylinders store it dissolved in acetone or DMF held in a porous filler.
反应Reactions
乙炔可发生加成、聚合、氧化和端基氢的取代。
Acetylene undergoes addition, oligomerisation, oxidation and substitution of its terminal hydrogens.
制氯乙烯
Making vinyl chloride
库切罗夫水合反应，经烯醇互变生成乙醛
Kucherov hydration via the enol to acetaldehyde
生成乙炔银白色沉淀，检验端炔
White silver acetylide precipitate, a test for terminal alkynes
三聚生成苯
Cyclotrimerisation to benzene
化学性质Chemical properties
使溴水和酸性 KMnO₄ 褪色，能与 H₂ 分步加成：在林德拉催化剂上停留在乙烯阶段。
Decolourises bromine water and acidic KMnO₄; hydrogenation over Lindlar's catalyst stops at ethylene.
燃烧火焰明亮并伴有浓烟：2 C₂H₂ + 5 O₂ → 4 CO₂ + 2 H₂O。
Burns with a bright, very sooty flame: 2 C₂H₂ + 5 O₂ → 4 CO₂ + 2 H₂O.
干燥的乙炔银、乙炔铜受撞击易爆炸。
Dry silver and copper acetylides explode on impact.
年表Timeline
- 1836
埃德蒙·戴维首次制得乙炔
Edmund Davy first prepares acetylene
- 1860
贝特洛命名为 acétylène
Berthelot names it acétylène
- 1892
威尔森发现电石的廉价生产方法
Willson finds a cheap route to calcium carbide
- 1903
氧炔焊接技术问世
Oxy-acetylene welding is introduced