A.
1,2-Cyclohexanedione. A
3-l. round-bottomed flask, fitted with stirrer and dropping funnel, is placed in a water bath containing a
copper coil through which cooling water may be circulated. In the
3-l. flask is placed
1708 g. (17.4 moles, 1.8 l.) of cyclohexanone (Note
1). Tap water is circulated through the cooling coil (Note
2), and a solution containing
387 g. (3 moles) of selenious acid (H2SeO3) (Note
3),
500 ml. of dioxane, and 100 ml. of water is added dropwise and with stirring to the
cyclohexanone over a period of 3 hours. The reaction mixture immediately turns yellow, and red amorphous
selenium gradually appears. Stirring is continued for 5 additional hours at water-bath temperatures and then for 6 more hours at room temperature. Removal of the bulky, amorphous
selenium is accomplished with the aid of a
6-in. Büchner funnel. The
selenium is returned to the reaction flask and extracted with
300 ml. of boiling 95% ethanol for 1 hour (Note
4). The solution, obtained by decantation from the compact gray
selenium, is combined with the above filtrate in a
4-l. distilling flask. Distillation under reduced pressure gives two fractions. The lower-boiling fraction (25–60°/16 mm.) consists mainly of
ethanol, water,
dioxane, and
cyclohexanone; the higher-boiling one (60–90°/16 mm.) contains
cyclohexanone and
1,2-cyclohexanedione with traces of water and
dioxane. The yield of crude product is approximately
322 g.
The higher-boiling fraction is redistilled (Note
5), and again two fractions, boiling at 25–75°/16 mm. and
75–79°/16 mm., are collected. The latter fraction is essentially pure
1,2-cyclohexanedione and crystallizes at 34° to ice-like crystals which become light yellow-green when exposed to the air; yield
202.5 g. (
60% based on
selenous acid). A considerable amount of light-brown, clear, resinous residue remains in the distilling flask.