Dehydration
Cyclohexanol gives cyclohexene through dehydration.
- Reagents
- Phosphoric acid catalyst
- Conditions
- Heat; cyclohexene is removed by distillation
- Reaction class
- Dehydration
- Equation
- C6H12O -> C6H10 + H2O
Overview
Cyclohexanol gives cyclohexene through dehydration.
Transformation
- Equation
- C6H12O -> C6H10 + H2O
- Reactants
- Cyclohexanol
- Products
- Cyclohexene + Water
- Reagents
- Phosphoric acid catalyst
- Environment
- Heat; cyclohexene is removed by distillation
- Reaction class
- Dehydration
- Mechanism
- dehydration
- Evidence level
- source-backed molecular example
Reference procedure
Cyclohexene preparation and purification
Cyclohexanol → cyclohexene + water
Materials and quantities
- Cyclohexanol
- Acid catalyst and work-up materials specified in the full method
Apparatus
- Heated reaction apparatus
- Distillation apparatus
- Separating funnel
Procedure
- Use the approved dehydration and distillation stages to separate volatile product from the reaction mixture.
- Separate the collected organic phase and dry it before any final purity measurement.
Work-up and isolation
- Record a boiling range and test a separate aliquot for unsaturation.
- An IR comparison can check loss of the alcohol feature; account for residual water.
Critical controls
- Decolourisation indicates unsaturation in the product mixture.
- Acid residues, water and unreacted alcohol require distinct purification steps.
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.
Liquid–liquid work-up
Separate the organic product layer from the aqueous reaction mixture, then wash and dry it before final purification.
Setup
- Identify which layer contains the product from density data or a small drop test; do not assume the organic layer is always on top.
- Invert gently during washing and vent frequently away from people, especially when carbonate wash produces carbon dioxide.
- Drain and retain both layers until product identity has been confirmed.
- Dry the isolated organic layer until the drying agent remains free-flowing, then decant or filter before final distillation.
Operating checks
- Remove the stopper before draining through the tap.
- Release pressure after each inversion during gas-forming washes.
- Record which layer was retained at every wash.
Drying an organic liquid
Remove residual water from a separated organic layer with a compatible anhydrous drying agent.
Setup
- Remove visible aqueous liquid before treating the organic phase.
- Mix with small portions of drying agent, allow contact and separate the clear liquid from the solid before final purification.
Operating checks
- Choose the agent for the product: a drying agent must not react with or strongly retain it.
- Drying removes water, not dissolved organic impurities; boiling-range or spectroscopic checks are still needed.
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
- Named cyclohexanol example; not a class-wide route prediction.
- Limitations
- Acid-catalysed elimination.
Related reactions
- Secondary alcohol oxidation: Cyclohexanol → Cyclohexanone
Oxidation removes hydrogen from the O-H group and its attached carbon, creating a C=O bond. Because that carbon already bonds to two other carbons, the product is a ketone and the six-membered ring is retained.
- Ketone reduction: Cyclohexanone → Cyclohexanol
Hydride adds to the planar carbonyl carbon while the pi electrons move onto oxygen. Subsequent protonation gives cyclohexanol; the existing carbon ring remains intact.
References
- Dehydration of alcoholsJim Clark · Chemguide · 2015
Named molecular transformation examples, checked 2026-09-08.
- A Level Chemistry A and B Practical Activities Support GuideOCR · OCR qualifications
PAG 5.2 covers cyclohexene preparation and purification; PAG 5.3 covers ethanol oxidation. Method summaries remain method overviews.
- 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.