C.
Diamantane. A
500-ml., three-necked flask, equipped with a
reflux condenser, a drying tube, a
magnetic stirring bar, and a dropping funnel is charged with
28 g. (0.11 mole) of fresh aluminum bromide and
100 ml. of cyclohexane (Note
7). The apparatus is flushed with
hydrogen bromide gas (Note
8). When the
aluminum bromide has dissolved,
100 g. (0.532 mole) of hydrogenated Binor-S is added dropwise to the rapidly stirred solution, and the reaction mixture refluxes for a short time without external heat. The course of the reaction is monitored by GC until no starting material remains (Note
9). Occasionally, an additional
5 g. portion of aluminum bromide, and application of external heat are needed to complete the reaction. The total reaction time is about 2–3 hours (Note
10). The hot
cyclohexane layer is carefully decanted, and the
aluminum bromide layer is extracted with five
200-ml. portions of hot cyclohexane.
Diethyl ether (400 ml.) is added to the cooled
cyclohexane extracts (Note
11), and the combined solvent fractions are washed with two 100-ml. portions of water and dried over anhydrous
magnesium sulfate. Evaporation of the solvent leaves a semi-solid residue, which is partially dissolved in about
100 ml. of pentane. The undissolved white solid,
diamantane, is collected by suction filtration. Additional
diamantane is obtained by concentrating the
pentane solution to a small volume and collecting the solid that precipitates. The total amount of
diamantane obtained, after drying, is
60–62 g. (
60–62%), m.p.
240–241° (closed tube) (Note
12). This product is sufficiently pure for most purposes, but it may be purified further by recrystallization from
pentane, giving white crystals, m.p.
244.0–245.4°.