碱性水解与酸化

水杨酸甲酯 → 水杨酸：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
1. 过量 NaOH 水溶液；2. 盐酸后处理
条件
与碱性水溶液一起加热回流，随后冷却并酸化
反应类别
碱性水解与酸化
方程式
C8H8O3 + 2NaOH + 2HCl -> C7H6O3 + CH3OH + 2NaCl + H2O

概览

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。

转化

水杨酸甲酯 → 水杨酸

方程式
C8H8O3 + 2NaOH + 2HCl -> C7H6O3 + CH3OH + 2NaCl + H2O
反应物
Methyl salicylate + 2 Sodium hydroxide + 2 Hydrogen chloride
产物
Salicylic acid + Methanol + 2 Sodium chloride + Water
试剂
1. 过量 NaOH 水溶液；2. 盐酸后处理
反应环境
与碱性水溶液一起加热回流，随后冷却并酸化
反应类别
碱性水解与酸化
机理
base-promoted acyl substitution followed by protonation
Evidence level
source-backed molecular example

参考步骤

Salicylic-acid recovery from methyl salicylate

Methyl salicylate → salicylate under alkaline hydrolysis → salicylic acid after acidification

物料与用量

  • 水杨酸甲酯
  • Aqueous sodium hydroxide
  • Hydrochloric acid for the prescribed work-up

仪器装置

  • 回流装置
  • Cooling bath
  • Suction-filtration apparatus

实验步骤

  1. Heat the ester with aqueous alkali under the source’s reflux conditions.
  2. Cool before controlled acidification to convert the carboxylate into the less soluble free acid.

后处理与分离

  1. Collect, wash and dry the precipitated solid; assess its melting range.
  2. Compare starting material and product chromatographically when a purity claim requires additional evidence.

关键控制条件

  • The immediate alkaline product is a salt; acidification is part of obtaining the named neutral product.
  • Both methyl salicylate and salicylic acid contain a free phenolic group; compare their other analytical signals.
  • Residual water or mother liquor changes mass and melting behaviour.

实验技术

Reflux setup

Boil the reaction while returning condensed vapour to the same flask, so volatile material is not continuously lost.

装置设置

  1. Charge the flask before fitting the condenser; do not fill the flask more than about half full.
  2. Run cooling water into the lower condenser inlet and out from the upper outlet.
  3. Keep the top of an ordinary reflux condenser open to the atmosphere unless the cited procedure specifies a pressure-rated closed system.
  4. Heat to a gentle, steady boil so the condensation line remains within the condenser and liquid returns continuously to the flask.

操作检查

  • Use an electric bath or mantle for flammable organic liquids; do not use a naked flame.
  • Start condenser water before heating and confirm that hoses are secure.
  • If addition is exothermic, complete the controlled addition and cooling stage before sustained reflux.

Filtration under reduced pressure

Collect an insoluble solid while drawing the liquid through a filter using reduced pressure.

装置设置

  1. Clamp the flask and seat the paper with the specified solvent before collecting a cooled crystal suspension.
  2. 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

  1. Load a small, compact sample and heat slowly near its expected melting temperature.
  2. 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.

薄层色谱

Compare starting material, product and reference samples using migration on the same stationary phase.

装置设置

  1. Draw a pencil baseline above the solvent and apply small, separate sample spots.
  2. Develop the plate, mark the solvent front promptly and visualise using the approved method.
  3. Calculate Rf as spot distance divided by solvent-front distance from the same baseline.

操作检查

  • Compare samples on the same TLC plate using the same solvent.
  • Protect eyes and skin during UV visualisation; avoid inhaling eluent vapour.

底物范围

适用范围
Hydrolysis of the methyl ester; acid work-up recovers salicylic acid.
来源说明
The net equation includes phenolic deprotonation and its reversal on acidification. Base and acid are used in sequence, not mixed at the outset; the initial hydrolysis product is a salt rather than neutral salicylic acid.

相关反应

参考文献

  1. The preparation of 2-hydroxybenzoic acidRoyal Society of Chemistry · RSC Education · 2023

    Official indexed content and teacher notes checked 2026-09-16. Supports methyl salicylate hydrolysis with aqueous sodium hydroxide followed by hydrochloric-acid work-up to salicylic acid. Exact work-up and isolation are in the linked practical source.

  2. The preparation of 2-hydroxybenzoic acidRoyal Society of Chemistry · RSC Education

    Alkaline ester hydrolysis followed by acidification, reduced-pressure filtration and purity assessment.

  3. 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.

  4. Using thin-layer chromatography to investigate the reaction: teacher notesRoyal Society of Chemistry · RSC Education

    Compares crude and recrystallised aspirin with a reference sample; extra spots suggest impurities.

  5. 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.

  6. Reflux and distillation – practical videosRoyal Society of Chemistry · RSC Education

    Explains the different purposes and apparatus arrangements for reflux and distillation, including organic preparation and work-up.

  7. Evaporation, filtration and crystallisation: teaching practical scienceRoyal Society of Chemistry · RSC Education

    Distinguishes filtration, crystallisation and post-16 reduced-pressure isolation.