The
chromic acid oxidizing reagent is prepared by dissolving
67 g. of chromium trioxide in 125 ml. of distilled water. To this solution is added
58 ml. of concentrated sulfuric acid (sp. gr. 1.84), and the salts which precipitate are dissolved by addition of a minimum quantity of distilled water; the total volume of the solution usually does not exceed 225 ml.
A solution of
64 g. (0.5 mole) of cycloöctanol (Note
1) in
1.25 l. of acetone (Note
1) is added to a
2-l. three-necked flask fitted with a
long-stem dropping funnel, a
thermometer, and a
powerful mechanical stirrer (Note
2). The vigorously agitated solution is cooled in a water bath to about 20°. The
chromic acid oxidizing reagent is added from the dropping funnel as a slow stream, and the rate of addition is adjusted so that the temperature of the reaction mixture does not rise above 35° (Note
3). The addition is continued until the characteristic orange color of the reagent persists for about 20 minutes (Note
4) and (Note
5). The volume of reagent added is about 120 ml.
The stirrer is removed, the mixture is decanted into a
2-l. round-bottomed flask, and the residual green salts are rinsed with two
70-ml. portions of acetone. The rinsings are added to the main
acetone solution and additional oxidizing agent is added, if necessary, to ensure complete reaction. The stirrer is replaced and
isopropyl alcohol is added dropwise until the excess
chromic acid is destroyed (Note
6). In small portions and with caution there is added
63 g. of sodium bicarbonate, and the suspension is stirred vigorously until the pH of the reaction mixture tests neutral (Note
7). The suspension is filtered and the filter cake is washed with
25 ml. of acetone. The filtrate is concentrated by distillation through a
75-cm. length of Vigreux column until the pot temperature rises to 80° and a water film begins to develop in the lower portions of the distillation column (Note
8). The cooled pot residue (about 110 ml.) is transferred to a
1-l. separatory funnel,
500 ml. of saturated sodium chloride solution is added, and the mixture is extracted with two
150-ml. portions of ether. The
ether extracts are combined, washed with a total of 25 ml. water in several portions, dried over anhydrous
magnesium sulfate, filtered, and the
ether distilled at atmospheric pressure. The pot residue is distilled under reduced pressure, b.p.
76–77° (10 mm.) (Note
9). The yield of
cycloöctanone is
58–60 g. (
92–96%), m.p.
40–42°.
An additional
2.2 g. (
4%) of
cycloöctanone may be obtained by addition of 250 ml. of water to the green salts formed during the reaction (Note
10), extraction of the mixture with
ether, distillation of the
ether, and addition of
12 ml. of acetone. To the
acetone solution there is added sufficient
chromic acid oxidizing reagent to permit the orange color of the reagent to persist (Note
11), and the mixture is processed as above.