B.
3-Pinanamine (3). A
1000-ml., three-necked, round-bottomed flask is fitted with a
gas-inlet tube, a
reflux condenser connected to a
mineral oil bubbler, and a
sealed mechanical stirrer. The system is flamed with a
Bunsen burner while being flushed with dry
nitrogen. The reaction vessel is then cooled under a
nitrogen stream in an ice bath while a slight positive pressure of
nitrogen is maintained. A solution of
3.12 g. (0.0824 mole) of sodium borohydride (Note
5) in
100 ml. of diglyme (Note
6) is added to the flask, followed by
27.25 g. (0.2004 mole) of (±)-α-pinene (Note
7). Hydroboration is achieved by dropwise addition of
15.6 g. (0.110 mole) of boron trifluoride diethyl etherate (Note
8) over a 15-minute period.
Di-3-pinanylborane (2) precipitates as a white solid. The ice bath is removed, and the reaction mixture is stirred at room temperature for 1 hour.
Hydroxylamine-O-sulfonic acid (1) (24.9 g., 0.220 mole) in 100 ml. of diglyme is added dropwise to the mixture over a 5-minute period (Note
9). The mixture is then heated in a 100°
oil bath for 3 hours. The mixture is cooled to room temperature, and
80 ml. of concentrated hydrochloric acid is added over a 5-minute period. The mixture is poured into 800 ml. of water and extracted with two
100-ml. portions of ether. The
ether layers are discarded, and the aqueous layer is made alkaline with
sodium hydroxide pellets (60–65 g. is needed). The aqueous layer is extracted with two
100-ml. portions of ether, the combined
ether extracts are dried over anhydrous
sodium sulfate, and the drying agent is removed by filtration. The filtrate is transferred to a 500-ml. ice-cooled flask fitted with a
magnetic stirring bar. A solution of 8
5–88% phosphoric acid (12 g., 0.10 mole) in 100 ml. of ethanol is added to the flask over 10 minutes with stirring. The precipitated colorless crystals are collected with suction on a Büchner funnel, and the salt is suspended in 300 ml. of hot water contained in a 1-l. flask. The mixture is heated and magnetically stirred in a 120–130° oil bath until all the salt has dissolved (
ca. 20–30 minutes) then quickly filtered with suction. Pure phosphate salt immediately precipitates as colorless plates, which are collected on a Büchner funnel and dried in a
desiccator. The yield is
16.6 g. (
33.1%). A second crop of
4.4 g. can be obtained by concentrating the mother liquor to about half its original volume. The total yield of pure phosphate salt is
21.0 g. (
41.8%), m.p.
275–280° (dec.) (Note
10). The salt is easily converted to free amine
3 by the following procedure: 10 g. (0.040 mole) of the salt is dissolved in
40 ml. of aqueous 3 M sodium hydroxide and extracted with two
50-ml. portions of ether. The combined extracts are dried over anhydrous
sodium sulfate, the drying agent is removed by filtration, and the solvent is removed under reduced pressure with a rotary evaporator. The residual oil is distilled, giving
5.9 g. (
93% from phosphate salt) of amine
3 as a colorless liquid, b.p.
83° (13 mm.) (Note
11).