A solution of
368 g. of 96% sulfuric acid in 664 ml. of water is cooled to room temperature and placed in a
3-l. three-necked flask provided with a mechanical stirrer, a thermometer, and a dropping funnel. To this acid solution is added
114 g. (1 mole) of 2-methylcyclohexanol (Note
1). A mixture of
220 g. (2.2 moles) of chromic oxide (Note
2) in
368 g. of 96% sulfuric acid and 664 ml. of water is added from the dropping funnel to the
2-methylcyclohexanol suspension at such a rate that the temperature of the mixture remains at 30 ± 2° (Note
3). Good agitation and an
ice bath are necessary to control the temperature in this range. The mixture is stirred at 30 ± 2° for 1 hour and then at room temperature until all the
chromic oxide is consumed (Note
4). The
sulfuric acid solution is extracted with
ether until the returns from the
ether extractions fall to an insignificant amount. Approximately 10 extractions with
200-ml. portions of ether are required (Note
5). The
ether extracts are combined, and the
ether is removed by distillation on the
steam bath. The resulting crude
δ-acetyl-n-valeric acid is a yellow liquid with a sharp odor and amounts to about
130 g. The crude acid is purified by distillation through a
30-in. Vigreux column, using a variable take-off, a reflux ratio of 3:1, and a pressure of 1 mm. A fore-run of approximately
30 g. of material distilling up to
122°/1 mm. is obtained. The main fraction which distils at
122–123°/1 mm. is pure
δ-acetyl-n-valeric acid and amounts to
66–79 g. (
46–55%). The pure acid is a colorless crystalline hygroscopic solid which melts (sealed capillary) at
34–35° and is miscible with water in all proportions. The literature records the melting point of
δ-acetyl-n-valeric acid as ranging from
31° to 42°.2,3,4