A
dry, 1-l., three-necked flask equipped with a
reflux condenser protected with a
calcium sulfate drying tube, a
250-ml., pressure-equalizing dropping funnel, and a
magnetic stirring bar is charged with
32 g. (0.10 mole) of camphor tosylhydrazone (Note
1) and
400 ml. of dry diethyl ether (Note
2). The flask is immersed in a
cold-water bath (20–25°), and the contents are stirred magnetically. About
50 ml. of dry ether is placed in the dropping funnel, and the addition rate is set at 2–3 ml./minute (Note
3). After this addition
150 ml. of 1.6 N (0.24 mole) methyllithium (Note
4) in
ether is added to the dropping funnel and dropped into the reaction flask over 1 hour (Note
5), while the cooling bath temperature is maintained at 20–25°. The yellow-orange solution is stirred for 8–9 hours, during which time
lithium p-toluenesulfinate precipitates and the solution develops a deep red-orange color. A small amount of water is carefully added to destroy excess
methyllithium before an additional 200 ml. is added. The layers are separated, the organic phase is washed with four 250-ml. portions of water, and the combined aqueous phases are shaken twice with
100-ml. portions of ether. After drying the combined ethereal extracts over anhydrous
sodium sulfate, the volume of the solution is reduced to 50–60 ml. by distillation of the
ether through a
25-cm. Vigreux column with gentle boiling on a
steam bath. After
100 ml. of distilled pentane (Note
6) is added to the orange solution, the solvent is again gently boiled away, reducing the volume to 30–50 ml. The addition and removal of
pentane is repeated two additional times to assure the complete removal of
ether, and the final volume of the solution of
2-bornene is reduced to 30–40 ml. The solution is added to an
80 × 5 cm. chromatography column packed with
500 g. of alumina (Note
7), and the product is eluted with
750 ml. of pentane. After concentration of the eluate by distillation of the solvent through a Vigreux column, the residue is transferred to a
50-ml. flask and distilled through a U-tube with the aid of an
oil bath and a heating lamp (Note
8). After collecting a forerun (
pentane and
2-bornene),
8.5–8.8 g. (
63–65%) of
2-bornene, m.p.
110–111° (lit.
2,3,4, 109–110°), is collected as colorless crystals in a cooled flask (Note
9). GC analysis
5 shows this product to be 98–99% pure, containing no
camphene or
tricyclene (Note
10).