Organic Syntheses, CV 3, 723
Submitted by Roland N. Icke, Burnett B. Wisegarver, and Gordon A. Alles.
Checked by H. R. Snyder and James H. Saunders.
1. Procedure
To
51.2 g. (1 mole) of 90% formic acid in a
500-ml. round-bottomed flask (Note
1), cooled in running tap water, is added slowly
24.2 g. (0.2 mole) of β-phenylethylamine. To the resulting clear solution are added
45 ml. (0.6 mole) of formaldehyde solution (concentration, 37%) (Note
2) and a small boiling stone. The flask is connected to a
reflux condenser and is placed in an
oil bath which has been heated to 90–100°. A vigorous evolution of
carbon dioxide begins after 2–3 minutes, at which time the flask is removed from the bath until the gas evolution notably subsides (15–20 minutes); then it is returned to the bath and heated at 95–100° for 8 hours.
After the solution has been cooled,
100 ml. of 4 N hydrochloric acid is added and the solution is evaporated to dryness under reduced pressure (
water pump) from a
water bath; the receiver is cooled in an
ice bath. The pale yellow syrupy residue (or crystalline solid) is dissolved in 60–75 ml. of water, and the organic base is liberated by the addition of
50 ml. of 18 N sodium hydroxide solution. The upper (organic) phase is separated, and the lower (aqueous) phase is extracted with two
30-ml. portions of benzene. The combined organic base and
benzene extracts are dried over
10 g. of anhydrous granular potassium carbonate (Note
3). After the
benzene has been distilled slowly under slightly reduced pressure from a
125-ml. Claisen flask, the pressure is lowered further, and the product is distilled. The yield of colorless
β-phenylethyldimethylamine boiling at
97–98°/22 mm. (Note
4) is
22–24.7 g. (
74–83%) (Note
5).
2. Notes
1. A flask of this size is used because of the tendency of the solution to froth during the gas evolution. Frothing usually is not bad with this amine but is quite bothersome when the higher aliphatic amines (
decylamine to
octadecylamine) are methylated.
2.
U.S.P. formaldehyde was used. The commercial aqueous-methanolic solution contains
37% formaldehyde by weight. It is sometimes called
"40% formalin" because 100 ml. of the solution contains 40 g. of formaldehyde.
3. If complete separation of the
benzene extracts from the aqueous solution is difficult, it is advantageous to dry the
benzene solution roughly over
10 g. of the anhydrous potassium carbonate and to decant the resulting clear solution into another flask where it may be dried over 5 g. of fresh drying agent. The spent drying agent is rinsed with
15–20 ml. of benzene, and the rinsings are added to the main solution.
4. Another boiling point is
66–68°/6 mm. If the product is distilled through a
short column (12–15 cm.) packed with glass helices, it boils constantly at
98°/22 mm. The recovery is somewhat lower when a column is used.
The product gives a negative carbylamine test and hence contains no significant amount of unchanged primary amine.
3. Discussion
This preparation is referenced from:
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