O acetylation
水杨酸 → 阿司匹林：查看反应物、产物、反应条件与来源依据，探索相关转化和合成路径。
- 试剂
- 乙酸酐；酸催化剂
- 条件
- 受控的酸催化乙酰化
- 反应类别
- O-乙酰化
- 方程式
- C7H6O3 + C4H6O3 -> C9H8O4 + CH3COOH
概览
水杨酸的酚氧从乙酸酐获得乙酰基。酰基取代形成酯，同时保留独立的羧基；质子转移生成伴生产物乙酸。
转化
- 方程式
- C7H6O3 + C4H6O3 -> C9H8O4 + CH3COOH
- 反应物
- Salicylic acid + Acetic anhydride
- 产物
- Aspirin + Ethanoic acid
- 试剂
- 乙酸酐；酸催化剂
- 反应环境
- 受控的酸催化乙酰化
- 反应类别
- O-乙酰化
- 机理
- 亲核酰基取代
- Evidence level
- source-backed molecular example
参考步骤
Aspirin crystallisation and purity assessment
Salicylic acid + ethanoic anhydride → acetylsalicylic acid + ethanoic acid
物料与用量
- 水杨酸
- Ethanoic anhydride with the reference phosphoric-acid catalyst
- Water for the prescribed quench and washing
仪器装置
- Dry reaction flask and condenser
- Water bath and cooling bath
- Suction-filtration apparatus
实验步骤
- Warm the acetylation mixture in a water bath as directed by the reference.
- Follow the source’s controlled water addition, then cool to promote crystallisation.
后处理与分离
- Collect and cold-wash the crystals by suction filtration; dry before weighing.
- Compare the melting range with a reference and assess free salicylate using a separate analytical aliquot.
关键控制条件
- Excess anhydride must be treated through the specified work-up before isolation.
- Dry crystals before measuring yield.
- Purple iron(III) colour reports free salicylate rather than aspirin itself.
实验技术
控温加热
应按来源给出的温度控温，选用适合溶剂、用量和目标温度的热源及容器。“加热”本身并不构成完整操作步骤。
装置设置
- 根据来源给出的温度选择浴液：水浴温度上限接近 100 °C；更高温度需使用合适的油浴、沙浴或指定加热装置。
- 固定好容器，合理放置温度探头，使其稳定测量反应体系或浴液温度，并避免接触加热器。
- 除非来源方法明确要求额定耐压设备，否则应保持装置可排气；不得将普通玻璃仪器临时改成密闭反应器。
- 逐步将混合物升至规定温度，达到工作温度后再开始计时。
操作检查
- 易燃有机溶剂应使用电加热，避免明火。
- 防暴沸颗粒应在加热前加入，不得加入热液体中。
- 若来源仅写“加热”，不得自行推定温度、时间或用量；应先取得针对具体底物的操作方法。
Filtration under reduced pressure
Collect an insoluble solid while drawing the liquid through a filter using reduced pressure.
装置设置
- Clamp the flask and seat the paper with the specified solvent before collecting a cooled crystal suspension.
- Retain the filtrate until the desired solid has been recovered.
操作检查
- Use vacuum-rated glassware and the laboratory-approved vacuum setup.
- Release the vacuum safely before shutting down the suction source. Filtration removes bulk liquid; further drying may be needed.
Melting range and solid purity
Record the interval from first melting to complete melting to compare a dry solid with reference data.
装置设置
- Load a small, compact sample and heat slowly near its expected melting temperature.
- Record the start and end temperatures for crude, purified and reference samples under comparable conditions.
操作检查
- Impurities often lower and broaden the range; residual solvent can do the same.
- A matching range alone cannot uniquely identify a compound. Decomposition is not ordinary melting.
底物范围
- 适用范围
- The phenolic OH of salicylic acid becomes an acetate ester.
- 来源说明
- The carboxyl group remains; identity and purity require separate analytical checks.
相关反应
- Acid hydrolysis: Aspirin → Salicylic acid
水进攻被酸活化的乙酰基羰基。酰基与氧的连接断裂并发生质子转移，恢复水杨酸的酚羟基；被移去的乙酰基形成乙酸。
- Alkaline hydrolysis and acidification: Methyl salicylate → Salicylic acid
氢氧根加成到酯羰基，置换甲氧基片段，后者形成甲醇。在碱性条件下，水杨酸盐基团处于去质子化状态；随后酸化可恢复中性羧酸和酚羟基。
参考文献
- A-level Chemistry 7405: Organic chemistryAQA · AQA specification
Checked 2026-09-16. Supports A-level topic coverage, including acid anhydrides, acylation and aspirin, amines, amino acids, polymers, synthesis and analysis. Coverage varies by examination board.
- The preparation of aspirinRoyal Society of Chemistry · RSC Education
Salicylic-acid acetylation with ethanoic anhydride, phosphoric-acid catalysis, crystallisation and suction filtration.
- The melting point of aspirinRoyal Society of Chemistry · RSC Education
Dry samples and observed melting ranges as evidence of purity rather than a stand-alone identity claim.
- Analysis of aspirin tablets on a microscaleRoyal Society of Chemistry · RSC Education
Supports iron(III) complex colour as a check for free salicylate in aspirin samples.
- Pearson Edexcel International Advanced Level Chemistry Student Practical GuidePearson Education Limited · Pearson qualifications · 2018
Supports the practical distinctions between reflux, distillation, liquid-liquid separation, washing and drying in organic preparations.
- Evaporation, filtration and crystallisation: teaching practical scienceRoyal Society of Chemistry · RSC Education
Distinguishes filtration, crystallisation and post-16 reduced-pressure isolation.