乙醇Ethanol

分子含乙基和羟基，C–O–H 键角约 109°。羟基使乙醇分子间形成氢键，沸点（78.4 °C）远高于相对分子质量相近的丙烷（−42 °C）和二甲醚（−24 °C）。乙醇的 pKa 约 15.9，酸性比水略弱，能与金属钠反应生成乙醇钠。

The molecule has an ethyl group and a hydroxyl group, with a C–O–H angle near 109°. Hydrogen bonding between hydroxyl groups gives a boiling point (78.4 °C) far above those of propane (−42 °C) and dimethyl ether (−24 °C), which have similar masses. Its pKa is about 15.9, slightly less acidic than water, and it reacts with sodium to give sodium ethoxide.

人类通过发酵酿酒已有九千年历史。中世纪炼金术士通过蒸馏得到浓缩酒精。1796 年洛维茨用脱水剂制得无水乙醇；1808 年索绪尔测定其组成；1858 年库珀提出乙醇的结构式。1828 年法拉第发现乙烯与硫酸反应可制乙醇，为后来的工业合成打下基础。

People have made fermented drinks for some nine thousand years. Medieval alchemists concentrated alcohol by distillation. In 1796 Lowitz obtained absolute ethanol using a desiccant; in 1808 de Saussure determined its composition; in 1858 Couper proposed its structural formula. In 1828 Faraday found that ethylene and sulfuric acid give ethanol, the basis of later industrial synthesis.

工业上用两种方法：一是淀粉或糖类在酵母作用下发酵，C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂；二是乙烯在磷酸催化下与水蒸气加成，CH₂=CH₂ + H₂O → CH₃CH₂OH（约 300 °C、6–7 MPa）。乙醇与水形成含乙醇 95.6% 的共沸物，制无水乙醇需用分子筛或苯共沸脱水。

Two industrial routes are used: yeast fermentation of starch or sugars, C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂, and the phosphoric-acid-catalysed hydration of ethylene, CH₂=CH₂ + H₂O → CH₃CH₂OH (about 300 °C, 6–7 MPa). Ethanol forms a 95.6% azeotrope with water, so absolute ethanol requires molecular sieves or azeotropic drying.

75% 乙醇溶液用于消毒；乙醇还用作溶剂、燃料（乙醇汽油）和合成乙醛、乙酸、乙酸乙酯的原料。乙醇在体内经醇脱氢酶氧化为乙醛，过量摄入会损害肝脏和神经系统。工业酒精常掺入甲醇，误饮会致盲甚至死亡。

A 75% solution is used as a disinfectant; ethanol is also a solvent, a fuel (gasohol) and a feedstock for acetaldehyde, acetic acid and ethyl acetate. The body oxidises it to acetaldehyde via alcohol dehydrogenase, and excess intake damages the liver and nervous system. Industrial alcohol is often denatured with methanol, which can cause blindness or death if drunk.