- Place 146 g (1 mol) of adipic acid, 360 ml (285 g, 6.2 mol) of absolute ethanol, 180 ml of toluene and 1.5 g of concentrated sulphuric acid in a 1 -litre round-bottomed flask, attach a short fractionating column connected to a down-ward condenser and heat in an oil bath at 115°C.
- When the acid has dissolved, an azeotropic mixture of alcohol, toluene and water commences to distil at 75 °C; the temperature of the oil bath may then be lowered to 100-110°C.
- Collect the distillate in a flask containing 150g of anhydrous potassium carbonate.
- Continue the distillation until the temperature at the top of the column rises to 78 °C.
- Shake the distillate thoroughly with the potassium carbonate, filter through a Buchner funnel or fluted filter paper and return the filtrate to the flask.
- Heat the flask again until the temperature rises to 78-80 °C (1).
- Transfer the warm residue to a flask of suitable size and distil under reduced pressure.
- Alcohol and toluene pass over first, the temperature rises abruptly and the diethyl adipate distils at 138°C/20mmHg (2). The yield is 195 g (96%).
Notes to keep in mind:
1. The distillate contains ethanol, toluene and
water, and may be dried with anhydrous potassium carbonate and used again for
esterification after the addition of the necessary quantity of alcohol.
2. The b.p. may rise several degrees towards the end of the
distillation owing to super-heating.
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