B.
(R)-(+)-α-Phenylethylamine. The residual salts (approximately 35 g.) obtained by concentration of the methanolic mother liquors from the initial crystallization of the (−)-amine (+)-hydrogen tartarate are treated successively with 160 ml. of water and
25 ml. of aqueous 50% sodium hydroxide. After the resulting mixture has been extracted with
ether, the extract is dried, concentrated, and distilled as previously described. The recovered amine amounts to
12.5–14.1 g. of colorless liquid, b.p.
79–80° (18 mm.),
[α]28D +23.8 to +24.7° (neat). From the weight and specific rotation data for this amine sample and the reported
2 specific rotation,
[α]25D +40.6° (neat), for the pure (+)-amine, the amount of excess (+)-amine present in the recovered amine sample is calculated. Typical values range from 0.06 to 0.07 mole of excess (+)-amine. A solution of this partially resolved amine in
90 ml. of 95% ethanol is heated to boiling and then treated with
180 ml. of an ethanolic solution containing a sufficient amount (0.03–0.035 mole) of concentrated sulfuric acid to convert the excess (+)-amine to its neutral sulfate salt (Note
6). The hot solution is allowed to cool to room temperature, and the crude
(+)-amine sulfate which separates as white needles (
7.8–9.3 g.) is collected on a filter and washed with
95% ethanol. The combined ethanolic mother liquors and washings are concentrated and allowed to cool to separate a second crop (
1.2–1.4 g.) of the crude (+)-amine sulfate. The combined crops of (+)-amine sulfate are dissolved in a minimum volume (about 45 ml. of hot water), and the resulting hot solution is diluted with
acetone until it is just saturated at the boiling point. After the solution has been allowed to cool to room temperature, the pure (+)-amine sulfate which separates as white needles, m.p.
240–265° dec. (
5.0–6.1 g.) is collected on a filter and washed with cold
95% ethanol. The combined mother liquors and washings are concentrated to dryness, and the residual solid is recrystallized from aqueous
acetone to separate additional crops (
2.6–2.8 g.) of the pure (+)-amine sulfate. The total yield of the pure amine sulfate is
7.8–8.9 g. (
45–51% on the basis of the starting
α-phenylethylamine).
A mixture of the pure
(+)-amine sulfate (7.8–8.9 g.) and 40 ml. of water is treated with
6.0 ml. of aqueous 50% sodium hydroxide and the resulting mixture is shaken with four
75-ml. portions of ether. The combined
ether extracts are washed with
50 ml. of saturated aqueous sodium chloride, dried over
magnesium sulfate, and concentrated by distillation of the
ether through a
30-cm. Vigreux column. The residual liquid is distilled under reduced pressure to separate
5.1–5.5 g. (
41–44%) of the (+)-amine as a colorless liquid, b.p.
85–86° (21 mm.),
n25D 1.5243–1.5248,
[α]29D +39.7° (neat) (Note
7).