Preparing cyclohexene from cyclohexanol template

A-level / AP / IB: cyclohexanol and 85% H₃PO₄ distilled from a heated flask, still head with thermometer at the side arm, condenser and a receiver in ice; then washed, dried and redistilled.

What the template shows

• Dehydrate an alcohol with phosphoric acid and distil off the alkene as it forms
• Water out
• Bulb level with the side arm; keep the reading below about 90 °C so little cyclohexanol distils (cyclohexene boils at 83 °C)
• Reaction flask
• Cyclohexanol, 85% phosphoric acid (catalyst; conc. H₂SO₄ works but chars and gives SO₂) and anti-bumping granules; heat gently
• Cloudy distillate
• Cyclohexene floats on water. Volatile and highly flammable: keep it cold and away from flames
• Then purify
• Shake with saturated NaCl in a separating funnel and keep the upper layer; dry over anhydrous CaCl₂ (or MgSO₄) until clear; redistil, collecting 81–85 °C. It decolourises bromine water
• Reaction setup

Drawn with 18 shapes – every one editable in MolDraw.

Sources

• Furniss et al., Vogel's Textbook of Practical Organic Chemistry, 5th ed., Longman 1989 Textbook
• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 17 Textbook
• Zubrick, The Organic Chem Lab Survival Manual, 10th ed., Wiley 2016 Textbook