Org. Synth. 1938, 18, 5
Submitted by M. T. Leffler
Checked by W. W. Hartman and E. J. Rahrs.
In a 5-l. round-bottomed flask, equipped with a reflux condenser connected to a gas trap (Note 1), are placed 2 l. (12.1 moles) of 20 per cent hydrochloric acid and 500 g. (5.05 moles) of allyl isothiocyanate (Note 2). The mixture is refluxed over a free flame until the upper layer of allyl isothiocyanate has completely disappeared, about fifteen hours being required for the hydrolysis. When the reaction is complete, the solution is poured into a 3-l. beaker and concentrated on the steam bath until crystals begin to form in the hot solution. This occurs when the volume is approximately 400 cc. (Note 3).
The warm residue is then diluted with water to a volume of 500–550 cc. and placed in a 2-l. three-necked, round-bottomed flask equipped with a 500-cc. dropping funnel, a mercury-sealed mechanical stirrer, and a condenser arranged for distillation. The lower end of the condenser is fitted to a receiver consisting of a 500-cc. suction flask, whose side arm is connected to a reflux condenser (Note 4). The receiver is placed in an ice-salt bath and the three-necked flask in a water bath. The temperature of the water bath is raised to 95–98°, the stirrer is started, and a solution of 400 g. (7.1 moles) of potassium hydroxide in 250 cc. of water is added dropwise from the funnel. As soon as the free hydrochloric acid is neutralized, the amine begins to distil. The rate of the addition of the alkali is regulated so as to maintain a dropwise distillation of allylamine and, after the addition is complete, heating and stirring are continued until all the amine has distilled.
The distillate is then dried over solid potassium hydroxide for twenty-four hours and finally over metallic sodium (Note 5). The allylamine is distilled from a water bath held at 70–78°, through a 12-in. fractionating column, into a receiver immersed in an ice bath. Two fractions are collected: up to 54°/746 mm., and 54–57°/746 mm. The lower fraction amounts to 14–16 g. and on redistillation yields 6–8 g. of pure material. The total yield of pure allylamine boiling at 54–57°/746 mm. is 200–210 g. (70–73 per cent of the theoretical amount).
It is desirable to use a gas trap in order to prevent vapors of allyl isothiocyanate
from escaping into the room. The gas trap described on p. 4
Eastman's "practical" grade (b.p. 150–152°
) of allyl isothiocyanate
was used in this preparation.
The rate of evaporation is greatly accelerated by allowing a stream of air to blow across the surface of the hot liquid. It is advantageous for the evaporation to proceed as far as possible in order to remove most of the free hydrochloric acid
, and no harm is done if it continues until the solution turns to a semi-solid mass of crystals.
Care must be taken throughout to prevent loss of the product by volatilization. Furthermore, the vapors should not be allowed to come into contact with the nasal passages, as violent sneezing is produced.
The distillate should be kept cold (5–10°) during the drying process and should be separated from the potassium hydroxide
before drying with sodium
has been prepared by the hydrolysis of allyl isothiocyanate
with dilute sulfuric1 or hydrochloric2 acid
Chemical Abstracts Nomenclature (Collective Index Number);
hydrochloric acid (7647-01-0)
potassium hydroxide (1310-58-3)
metallic sodium (13966-32-0)
allyl isothiocyanate (57-06-7)
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