Hydrolysis
Hydrolysis converts esters back into carboxylic acid products.
- Reagents
- dilute H2SO4(aq)
- Conditions
- heat under reflux
- Reaction class
- hydrolysis
- Equation
- R-CO2R' + H2O <-> R-CO2H + R'OH
Overview
Hydrolysis converts esters back into carboxylic acid products.
Transformation
- Equation
- R-CO2R' + H2O <-> R-CO2H + R'OH
- Reagents
- dilute H2SO4(aq)
- Environment
- heat under reflux
- Reaction class
- hydrolysis
- Mechanism
- ester hydrolysis
- Evidence level
- textbook core
Reference procedure
Salicylic acid from ester hydrolysis
Methyl 2-hydroxybenzoate → 2-hydroxybenzoic acid after alkaline hydrolysis and acidification
Materials and quantities
- Methyl 2-hydroxybenzoate
- Aqueous alkali and acid for the source’s work-up
Apparatus
- Reflux apparatus
- Cooling vessel
- Reduced-pressure filtration equipment
Procedure
- Use the specified alkaline hydrolysis stage; the immediate product is a carboxylate salt.
- Cool and acidify as directed to obtain the less soluble carboxylic acid as a solid.
Work-up and isolation
- Collect, wash and dry the crystals; calculate yield from the limiting reagent.
- Assess a melting range and, where available, compare TLC with reference material.
Critical controls
- This reference preparation uses alkaline hydrolysis followed by acidification, whereas acid hydrolysis is reversible.
- Dry crystals before weighing; retained solvent increases recorded mass.
Practical techniques
Reflux setup
Boil the reaction while returning condensed vapour to the same flask, so volatile material is not continuously lost.
Setup
- Charge the flask before fitting the condenser; do not fill the flask more than about half full.
- Run cooling water into the lower condenser inlet and out from the upper outlet.
- Keep the top of an ordinary reflux condenser open to the atmosphere unless the cited procedure specifies a pressure-rated closed system.
- Heat to a gentle, steady boil so the condensation line remains within the condenser and liquid returns continuously to the flask.
Operating checks
- 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.
Setup
- 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.
Operating checks
- 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.
Recrystallisation
Purify a solid using its greater solubility in hot solvent than in cold solvent.
Setup
- Choose a compatible solvent and dissolve the crude solid in the minimum practical amount of hot solvent.
- Remove insoluble matter while hot if required; cool the clear solution before collecting the crystals.
Operating checks
- Excess solvent reduces recovery; some product remains in the mother liquor.
- Wash with a small amount of cold solvent and dry before weighing. Wet crystals give misleading yields.
Melting range and solid purity
Record the interval from first melting to complete melting to compare a dry solid with reference data.
Setup
- 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.
Operating checks
- 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.
Thin-layer chromatography
Compare starting material, product and reference samples using migration on the same stationary phase.
Setup
- Draw a pencil baseline above the solvent and apply small, separate sample spots.
- Develop the plate, mark the solvent front promptly and visualise using the approved method.
- Calculate Rf as spot distance divided by solvent-front distance from the same baseline.
Operating checks
- Compare samples on the same TLC plate using the same solvent.
- Protect eyes and skin during UV visualisation; avoid inhaling eluent vapour.
Scope and limitations
- Scope
- Acid-catalysed ester hydrolysis under reflux gives a carboxylic acid and an alcohol in a reversible reaction.
- Limitations
- Alkaline hydrolysis is not represented by this equation: it gives a carboxylate salt and an alcohol irreversibly, and requires a separate acidification step to give the carboxylic acid.
Related reactions
- Oxidation: Alcohols → Carboxylic acids
Full oxidation of a primary alcohol gives a carboxylic acid.
- Complete oxidation: Primary alcohols → Carboxylic acids
Full oxidation of a primary alcohol gives a carboxylic acid.
- Reduction: Carboxylic acids → Primary alcohols
Reduction of a carboxylic acid gives a primary alcohol.
- Oxidation: Aldehydes → Carboxylic acids
Oxidation of an aldehyde gives a carboxylic acid.
- Hydrolysis: Nitriles → Carboxylic acids
Nitriles can be hydrolysed to carboxylic acids, splitting the old aggregate nitrile-to-amide route into a single functional-group conversion.
- Activation for amide formation: Carboxylic acids → Amide chemistry
Carboxylic acids or activated acid derivatives connect to amide-bond formation.
- Esterification: Carboxylic acids → Esters
Carboxylic acids react with alcohols to form esters.
- Esterification co reactant: Alcohols → Esters
Alcohols combine with carboxylic acids to form esters.
- Hydrolysis co product: Esters → Alcohols
Hydrolysis of an ester also regenerates the alcohol component.
- Chlorination: Carboxylic acids → Acyl chlorides
PCl5 converts carboxylic acids into acyl chlorides.
- Chlorination with thionyl chloride: Carboxylic acids → Acyl chlorides
Thionyl chloride converts carboxylic acids into acyl chlorides with sulfur dioxide and hydrogen chloride as by-products.
- Hydrolysis: Acyl chlorides → Carboxylic acids
Water hydrolyses acyl chlorides to carboxylic acids, releasing hydrogen chloride.
- Acylation: Acyl chlorides → Esters
Alcohol acylation converts acyl chlorides into esters.
- Carboxylation: Grignard reagents → Carboxylic acids
Grignard carboxylation gives carboxylic acids after acidic work-up.
- Grignard carboxylation co reactant: Carbon dioxide → Carboxylic acids
Carbon dioxide plus a Grignard reagent gives a carboxylic acid after acidic work-up.
- Salt formation: Carboxylic acids → Carboxylate salts
Carboxylic acids react with bases, carbonates and reactive metals to form carboxylate salts.
References
- Organic Chemistry: Chemistry of EstersJohn McMurry · OpenStax Organic Chemistry · 2023
Distinguishes reversible acid-catalysed ester hydrolysis from alkaline saponification, which gives a carboxylate ion until a separate acidification step.
- The preparation of 2-hydroxybenzoic acidRoyal Society of Chemistry · RSC Education
Alkaline ester hydrolysis followed by acidification, reduced-pressure filtration and purity assessment.
- Purifying by recrystallisationRoyal Society of Chemistry · RSC Education
Solvent selection, soluble and insoluble impurities, recovery losses and residual-solvent error.
- 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.
- 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.
- 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.
- 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.
- Evaporation, filtration and crystallisation: teaching practical scienceRoyal Society of Chemistry · RSC Education
Distinguishes filtration, crystallisation and post-16 reduced-pressure isolation.