Partial oxidation
Ethanol is oxidised to ethanal.
- Reagents
- K2Cr2O7 / dilute H2SO4
- Conditions
- Controlled warming; remove the aldehyde by distillation
- Reaction class
- Partial oxidation
- Equation
- CH3CH2OH + [O] -> CH3CHO + H2O
Overview
Ethanol is oxidised to ethanal.
Transformation
- Equation
- CH3CH2OH + [O] -> CH3CHO + H2O
- Reagents
- K2Cr2O7 / dilute H2SO4
- Environment
- Controlled warming; remove the aldehyde by distillation
- Reaction class
- Partial oxidation
- Mechanism
- alcohol oxidation
- Evidence level
- source-backed molecular example
Reference procedure
Selective oxidation to ethanal
Ethanol → ethanal
Materials and quantities
- Ethanol
- Acidified dichromate; use the cited method’s quantities
Apparatus
- Distillation apparatus
- Receiver
Procedure
- Collect the volatile product by distillation as it forms to limit further oxidation.
- Record the oxidant colour change separately from the product observations.
Work-up and isolation
- Use the cited aldehyde test on a separate aliquot; compare an IR spectrum where available.
Critical controls
- Record the orange-to-green change and analyse the distillate, which may contain water and alcohol.
- Control flammable vapour and segregate chromium-containing waste.
Practical techniques
Distillation setup
Rearrange the apparatus to collect a volatile product or fraction instead of returning condensate to the reaction flask.
Setup
- Position the thermometer bulb at the entrance to the condenser so it measures vapour entering the condenser.
- Run cooling water into the lower condenser connection and out through the upper connection.
- Heat gradually and collect only the fraction specified by the cited boiling range or procedure.
Operating checks
- Do not distil a flask to dryness.
- Use an electric heat source for flammable mixtures.
- Change from reflux to distillation only after heating has stopped and the apparatus has cooled enough to handle safely.
Infrared evidence for functional-group change
Use functional-group absorptions and the fingerprint pattern to test a proposed transformation.
Setup
- Check sample identity, background and axis units before assigning absorptions.
- Compare the starting material and product: oxidation may introduce C=O while removing an alcohol O–H feature.
Operating checks
- Water, solvent and unreacted substrate can contribute bands.
- A carbonyl band alone does not distinguish every aldehyde, ketone, acid and ester. Use reference data and complementary evidence; no simulated trace is a measurement.
Scope and limitations
- Scope
- Ethanol; primary alcohol.
- Limitations
- Cr(VI) oxidising reagent; continued oxidation produces ethanoic acid.
Related reactions
- Iodoform reaction: Ethanal → Triiodomethane products
Ethanal gives triiodomethane and methanoate in the alkaline iodine iodoform reaction.
- Iodoform reaction: Ethanol → Triiodomethane products
Ethanol is oxidised and cleaved by alkaline iodine to give triiodomethane and methanoate.
- Oxidation: Ethanol → Ethanoic acid
Ethanol is oxidised to ethanoic acid.
- Oxidation: Ethanal → Ethanoic acid
Ethanal is oxidised to ethanoic acid.
- Reduction: Ethanal → Ethanol
Ethanal is reduced to ethanol.
- Esterification: Ethanol → Ethyl acetate
Ethanoic acid and ethanol combine reversibly to form ethyl acetate and water.
- Acid hydrolysis: Ethyl acetate → Ethanol
Ethyl acetate and water react reversibly to form ethanoic acid and ethanol.
- Hydration: Ethene → Ethanol
Ethene gives ethanol through hydration.
- Dehydration: Ethanol → Ethene
Ethanol gives ethene through dehydration.
- Intermolecular dehydration: Ethanol → Diethyl ether
Protonation turns one ethanol OH group into a better leaving group. The oxygen of another ethanol molecule displaces water, and deprotonation gives diethyl ether; stronger dehydration conditions instead favour ethene.
- Hydrolysis: Bromoethane → Ethanol
Hydroxide attacks the saturated carbon bearing bromine while the C-Br bond breaks. This primary-substrate SN2 route replaces bromide with OH and preserves both carbon atoms; aqueous conditions favour this branch over elimination.
- Acid hydrolysis: Ethyl butyrate → Ethanol
Water attack and proton transfers permit the ethoxy fragment to leave as ethanol. Re-forming the carbonyl produces butanoic acid on the other branch.
References
- Oxidation of alcoholsJim Clark · Chemguide · 2015
Named molecular examples and reaction scope, checked 2026-09-08.
- Core practical 5: Investigate the oxidation of ethanolPearson Education Limited · Pearson qualifications
Distillation versus reflux in primary-alcohol oxidation; product tests and chromium waste controls.
- 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.
- Infrared spectroscopy: introductionRoyal Society of Chemistry · RSC Education
Molecular vibrations, functional-group absorptions and fingerprint comparison; no fabricated sample spectra.