重结晶Recrystallization (chemistry)

理想溶剂对目标物在高温时溶解度大、低温时溶解度小，对杂质要么溶解度很大（留在母液中）要么很小（热滤除去），且不与目标物反应、沸点适中、易除去。晶体生长时晶格倾向于只容纳相同分子，杂质被排斥在外，所以缓慢冷却得到的晶体更纯、更大。常用溶剂有水、乙醇、丙酮、乙酸乙酯、甲苯等，也可用“良溶剂-不良溶剂”混合溶剂。

An ideal solvent dissolves the compound well when hot and poorly when cold, dissolves impurities either very well (so they stay in solution) or very poorly (so they are filtered off hot), does not react, boils at a convenient temperature and is easy to remove. A growing crystal lattice tends to accept only identical molecules and rejects impurities, so slow cooling gives purer, larger crystals. Common solvents are water, ethanol, acetone, ethyl acetate and toluene, or a 'good solvent–poor solvent' mixture.

选择溶剂 → 加热溶解（用最少量热溶剂刚好溶解）→ 必要时加活性炭脱色 → 趁热过滤（预热漏斗或用热水漏斗防止晶体在滤纸上析出）→ 室温缓慢冷却、再冰浴冷却结晶（必要时摩擦瓶壁或加晶种诱导）→ 抽滤 → 用少量冷溶剂洗涤 → 干燥 → 测熔点检验纯度。

Choose a solvent → dissolve in the minimum of hot solvent → decolourise with activated charcoal if needed → filter hot (with a pre-warmed or hot-water funnel so crystals do not form on the paper) → cool slowly to room temperature and then in ice (scratching the flask or seeding if needed) → filter by suction → wash with a little cold solvent → dry → check purity by melting point.

在色谱技术普及之前，重结晶是有机化学家获得纯化合物的主要手段，熔点和混合熔点是鉴定纯度和身份的基本方法。工业上制药、精细化工和制糖业大量采用结晶工艺，药物晶型的控制直接影响溶解度和生物利用度。

Before chromatography became widespread, recrystallisation was organic chemists' main route to pure compounds, and melting and mixed melting points were the basic tests of purity and identity. Industrial pharmaceuticals, fine chemicals and sugar rely heavily on crystallisation, and control of drug crystal forms directly affects solubility and bioavailability.