A.
9,9-Dibromobicyclo[6.1.0]nonane. A dry
3-l. three-necked flask is fitted with a
glass stopper, stirrer, and
condenser. The flask is kept under a positive
nitrogen pressure by means of a
gas-trap arrangement connected to the top of the condenser (Note
1). The flask is quickly charged with
2 l. of anhydrous t-butyl alcohol (Note
2) and
73 g. (1.87 g. atoms) of potassium metal.
(Caution! See earlier volume2 for handling of this metal.) The flow of
nitrogen is stopped and the mixture is stirred and boiled under reflux until the
potassium has reacted,
hydrogen being liberated through the trap. The condenser is arranged for distillation by means of an
adapter. The glass stopper is replaced by a
pressure-equalized dropping funnel with the
nitrogen inlet connected to the top. About
1.5 l. of t-butyl alcohol (Note
3) is then distilled into a predried flask under an atmosphere of
nitrogen. A
water pump is then connected, the nitrogen inlet is closed, and the distillation is continued under reduced pressure while the three-necked flask is gradually heated to 150° in an
oil bath. Finally, the water pump is replaced by an
oil pump and the white remaining solid is heated at 150° under a pressure of 0.1–1 mm. for 2 hours. The connection to the vacuum system is closed, the oil bath removed, and
nitrogen again introduced. The condenser with adapter is replaced by a glass stopper, and the flask is cooled in an
ice-salt bath.
Freshly distilled
cis-cyclooctene, 178 g. (214 ml., 1.62 moles) (Note
4) and
200 ml. of sodium-dried pentane (Note
5) are introduced to the flask, and the dropping funnel is charged with
420 g. (148 ml., 1.66 moles) of bromoform (Note
6). The
bromoform is added dropwise to the stirred slurry over a period of 6–7 hours, the color of the reaction mixture changing gradually from light yellow to brown. When the addition is complete, the reaction mixture is allowed to warm to room temperature and left stirring overnight. Water (400 ml.) is added to the reaction mixture followed by enough
10% aqueous hydrochloric acid to neutralize the slightly basic solution. The reaction mixture is transferred to a
separatory funnel and the organic layer is separated. The aqueous layer is extracted with three
50-ml. portions of pentane, and the combined
pentane solutions are washed with three 50-ml. portions of water. The
pentane solution is dried over anhydrous
magnesium sulfate, filtered, and stripped of solvent on a
rotary evaporator. Distillation of the residue yields
237–299 g. (
52–65%) of
9,9-dibromobicyclo[6.1.0]nonane, b.p.
62° (0.04 mm.),
n23D 1.5493–1.5507 (Note
7).