CAUTION: All operations should be conducted in an efficient fume cupboard owing to the toxicity of pyridine and benzene.
- In a 250-ml, round-bottomed three-necked flask, provided with a dropping funnel, stirrer and thermometer, place 15.8g (16.1ml, 0.2 mol) of dry pyridine and 25 ml of dry benzene.
- Stir and add rapidly 14.8g (15.5 ml, 0.1 mol) of heptanoyl chloride; the temperature rises slightly and a pyridinium complex separates.
- Introduce 13.0g (14.1ml, 0.1 mol) of heptanoic acid with stirring, over a period of 5 minutes; the temperature rises to 60-65 °C and pyridine hydrochloride is formed.
- Continue the stirring for 10 minutes and collect the hygroscopic pyridine hydrochloride as rapidly as possible on a chilled Buchner or sintered glass funnel, and wash it with two 25-ml portions of dry benzene.
- Remove the benzene from the filtrate under reduced pressure on a water bath, and distil the residue through a short fractionating column.
- Collect the heptanoic anhydride at 170-173 °C/15mmHg; the yield is 20g (83%).
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