Source: http://www.orgsyn.org/demo.aspx?print=1&showprint=1&prep=CV6P0378
Timestamp: 2019-04-21 23:17:50+00:00

Document:
Submitted by Tamara M. Gund, Wilfried Thielecke, and Paul v. R. Schleyer1.
Checked by H. Gurien, R. Regenye, and A. Brossi.
A. Binor-S.2 A 2-l., three-necked flask equipped with Teflon sleeves (Note 1), a thermometer, a condenser, a dropping funnel, and a mechanical stirrer is flushed with nitrogen and charged with 200 g. (2.18 moles) of freshly distilled norbornadiene (Note 2), 400 ml. of dry toluene, and 7.8 g. of cobalt bromide–triphenylphosphine catalyst (Note 3). While stirring at room temperature, 2.1 ml. of boron trifluoride diethyl etherate co-catalyst (Note 4) is added dropwise. The mixture is heated slowly to 105°, and the heating mantle is lowered. The ensuing exothermic reaction maintains the temperature at 105–110° for 15 minutes. When the temperature begins to fall, the mantle is raised, the mixture is brought to the reflux temperature, and stirring and refluxing are continued for 12 hours. The cooled mixture is diluted with 650 ml. of dichloromethane, transferred to a separatory funnel, and washed with three 650-ml. portions of water. The organic phase is dried over anhydrous magnesium sulfate, and the solvents are evaporated at reduced pressure. The residual crude material, 185–203 g., is distilled at 106–107° (1.5 mm.), giving 165–170 g. (82–85%) of Binor-S, which solidifies on cooling to a white solid, m.p. 59–63°.
B. Tetrahydro-Binor-S. Binor-S (135.0 g., 0.734 mole) is dissolved in 670 ml. of glacial acetic acid containing 5.7 ml. of concentrated hydrochloric acid. To this solution is added 1.0 g. of platinum oxide catalyst. The reaction mixture is hydrogenated at 200 p.s.i. hydrogen pressure and 70° for 3 hours, using a 1200-ml., glass-lined autoclave (Note 5). After cooling to room temperature, the catalyst is removed with suction filtration, and water (ca. 1.5 l.) is added to the filtrate until two layers form. The bottom layer, containing only tetrahydro-Binor-S, is removed, and the top layer, consisting of a mixture of acetic acid and water, is extracted with one 400 ml. and two 100-ml. portions of dichloromethane. The combined dichloromethane–tetrahydro-Binor-S layers are washed twice with 100 ml. of water, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residual tetrahydro-Binor-S is purified by distillation under reduced pressure, b.p. 105–110° (1.5 mm.), giving 125–130 g. (90–94%) of colorless liquid (Note 6).
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°.
1. Teflon sleeves were used to keep the joints from freezing.
2. Once distilled, norbornadiene may be stored below 0°. Samples as old as 2 weeks were used successfully.
3. This catalyst3 is prepared in quantitative yield by refluxing by 200 ml. benzene solution containing 10 g. (0.046 mole) of anhydrous cobalt dibromide and 24.4 g. (0.0931 mole) of triphenylphosphine. A color change is observed, and the blue-green solid that precipitates on cooling to room temperature is filtered and dried. This catalyst, stored in a dry atmosphere, appears to be active indefinitely.
4. Boron trifluoride etherate may be used without prior distillation only if fresh material is available. Care must be taken with this reagent because of fuming. The dimerization does not proceed without this co-catalyst.
5. At 70° Binor-S remains in solution, and the uptake of hydrogen is rapid. The checkers have observed that occasionally hydrogen uptake is incomplete, and an additional 1 g. of catalyst must be added to complete the absorption of hydrogen. The submitters carried out the hydrogenation in a large-scale Parr apparatus under three atmospheres of pressure with similar results.
6. After a small solvent-containing forefraction, which is discarded, essentially all of the material should distill in the indicated range, but occasionally material boiling as high as 130° (1.5 mm.) is obtained. This is included in the product.
7. Either carbon disulfide or cyclohexane may be used with comparable yields. The advantage of carbon disulfide is the greater solubility of diamantane. When extracting with cyclohexane, a boiling solution must be used to increase solubility. However, cyclohexane is less poisonous, does not have a foul odor, and gives a whiter product. Therefore, the use of carbon disulfide was not examined by the checkers. Use of dichloromethane has been reported2 to lead to an 82% yield.
8. Flushing the apparatus with hydrogen bromide may not be necessary, especially for small-scale runs.
9. A Carbowax 20M or 1500 GC column at a temperature of 180° may be used. Diamantane has a shorter retention time than tetrahydro-Binor-S. The checkers used a 10% OV101 GCQ column, 100/120, at 200°; retention times are Binor-S, 11.5 minutes; tetrahydro-Binor-S, 7.6 minutes; diamantane, 6.2 minutes.
10. About 30 minutes after the addition of tetrahydro-Binor-S is complete, the reaction mixture begins to cool and external heat must be supplied to continue the refluxing and complete the reaction. If GC monitoring reveals that the rearrangement is proceeding slowly, an additional 0.5 g. of aluminum bromide is added and refluxing is continued until all the starting material is converted to product.
11. Addition of ether prevents crystallization of the diamantane from cooled cyclohexane.
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