The oxidation of cyclohexanol by nitric acid

In this experiment, students convert cyclohexanol to 1,6-hexanedioic acid (adipic acid) using a ring opening oxidation with nitric acid. Since 1,6-hexanedioic acid is a solid, a melting point measurement can be done on the product (mp 152 °C).

This practical should take 20 minutes.

Equipment

Apparatus

• Eye protection
• Beaker, 100 cm³
• Beaker, 50 cm³
• Hot plate
• Plastic pipettes x3
• Test tube

Chemicals

• Cyclohexanol
• Nitric acid (ca 5 mol dm^–3, concentrated nitric acid: deionised water 1:1)

Health, safety and technical notes

• Read our standard health and safety guidance
• Students must wear suitable eye protection (splash proof goggles to BS EN166 3). The reaction should be done in a fume cupboard.
• Cyclohexanol is a skin and respiratory irritant and is harmful if swallowed or inhaled (see CLEAPSS HazCard HC084c).
• Nitric acid, HNO₃ (aq), 5 mol dm^–3, is CORROSIVE (see CLEAPSS HazCard HC067).

Procedure

1. Half-fill a 100 cm³ beaker with deionised water, and heat to 80–90 °C.
2. Add 1 cm³ of nitric acid to a test-tube and place in the water bath.
3. Carefully add six drops of cyclohexanol to the test-tube. You will notice some bubbling and the nitric acid turns brown.
4. Leave for 10 min.
5. Remove the test-tube from the water bath and allow to cool to room temperature.
6. Cool further in an ice bath – crystals should form.
7. Filter off the crystals, wash with 2 cm³ of deionised water and dry them.
8. Measure the melting point of your product.

Observations

A white, crystalline solid should slowly form when the test-tube is cooled in the ice bath. The solid might be slightly brown in colour due to impurities when first filtered off, but this discolouration is removed by washing with water.

Student questions

• What is the melting point of your product?
• How does it compare with the value from data books?
• Can you explain any variations?