CAUTION: This preparation must be carried out in an
efficient fume cupboard and the apparatus should be sited behind a
safety-screen for extra protection.
- Into a 500-ml three-necked flask, fitted with a dropping funnel, a mechanical stirrer and an efficient reflux condenser, place 190 ml (270 g) of concentrated nitric acid, d1.42.
- Since oxides of nitrogen are evolved in the subsequent oxidation, the reaction should be carried out in a fume cupboard, or the oxides of nitrogen are led by a tube from the top of the condenser to a water trap.
- Heat the nitric acid to boiling, set the stirrer in motion, add a few drops of cyclohexanol and make certain that these are acted upon by the acid before adding more; an explosion may result if cyclohexanol is allowed to accumulate in the acid.
- Once the reaction has started, add 50 g (0.5 mol) of cyclohexanol through the dropping funnel at such a rate that all is introduced in 2-3 hours.
- Keep the reaction mixture at the boiling point during the addition of the cyclohexanol and for a further period of about 15 minutes in order to complete the oxidation.
- Pour the warm reaction mixture into a beaker; upon cooling, the adipic acid crystallises.
- Filter on a large sintered glass funnel, and wash with 20 ml of cold water.
- Recrystallise the crude acid from 70ml of concentrated nitric acid; filter and wash as above. The yield of recrystallised adipic acid, m.p. 152°C, is 40 g (55%).
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