OCR A Level Chemistry

Revision Notes

1.2.3 Preparation of Cyclohexene

Test Yourself

PAG 5.2: Preparation of Cyclohexene

Preparation and Purification of Cyclohexene

  • In this experiment an alkene, cyclohexene, will be prepared by dehydration of an alcohol, cyclohexanol, using an acid catalyst such as phosphoric acid

C6H11OH rightwards arrow with blank on top C6H10 + H2O

  • This is one of the most common methods of preparing alkenes
  • The crude product is contaminated with water, unreacted alcohol, phosphoric acid and some side products
  • Treatment with a saturated solution of sodium hydrogen carbonate removes traces of acid and a final wash with water removes any remaining carbonate
  • Addition of solid calcium chloride will remove remaining water
  • The mechanism for the reaction is shown below - you do not need to know this, but you could be asked in a questions to draw in the relevant charges or lone pairs

06486c7d-dd7d-4003-8009-794254709f0e

Elimination mechanism for cyclohexanol

Preparation

  • Pour approximately 20 cm3 of cyclohexanol into a weighed 50 cm3 pear shaped flask
  • Slowly add 8 cm3 of concentrated phosphoric acid into the flask using a pipette 
  • Add a few anti-bumping granules to the flask and assemble the distillation apparatus, so that the contents of the flask may be distilled
  • Heat the flask gently using an electric heater or water bath
  • Collect the distillate 

Purification of ethyl ethanoate

Purification

  • Pour the distillate into a separating funnel and add 10 cm3 of sodium hydrogen carbonate solution, this will remove unreacted acid and acidic impurities in the organic liquid  
  • Shake the funnel and allow the mixture to separate, release the pressure built up in the funnel
  • Carefully run off the lower aqueous layer and then transfer the upper layer which contains the crude cyclohexene into a conical flask 
  • Add solid anhydrous calcium chloride to the crude cyclohexene to remove water
  • Stopper the flask, shake the contents and allow to stand 
  • Once clear, transfer the liquid to a clean, dry beaker
  • A small portion of the distillate can be tested with bromine water to confirm if the product is an alkene
    • The colour change will be from orange brown to colourless

Separation of ethyl ethanoate, downloadable AS & A Level Chemistry revision notes

A separating funnel allows the product to be cleaned and isolated

You've read 0 of your 0 free revision notes

Get unlimited access

to absolutely everything:

  • Downloadable PDFs
  • Unlimited Revision Notes
  • Topic Questions
  • Past Papers
  • Model Answers
  • Videos (Maths and Science)

Join the 80,663 Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Philippa

Author: Philippa

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.