Organic Syntheses, Coll. Vol. 5, p.121 (1973); Vol. 43, p.6 (1963).
Caution! Contact with 2-bromoallylamine
can cause severe eye and skin irritation. This preparation should be carried out in a good hood
, and the operator should wear protective goggles and rubber gloves.
A. 2-Bromoallylhexaminium bromide
. A 2-l. three-necked flask
fitted with a Hershberg stirrer
a dropping funnel
, and a condenser is charged with a solution of 154 g. (1.10 moles) of hexamethylenetetramine (Note 1)
in 1250 ml. of chloroform
. The solution is stirred and heated under reflux while 200 g. (1.00 mole) of 2,3-dibromopropene (Note 2)
is added dropwise over a period of 1 hour. Precipitation of the product is noted soon after the first addition of 2,3-dibromopropene
. After the addition is complete, the reaction mixture is stirred under reflux for 3 hours and allowed to stand overnight. The mixture is cooled in an ice bath
, and the salt is collected by suction filtration. After air-drying, the crude yellow 2-bromoallylhexaminium bromide
weighs 292–308 g.
) and melts at 183–186°
. Crude 2-bromoallylhexaminium bromide (204 g., 0.60 mole)
is dissolved in a warm solution prepared from 400 ml. of water, 2 l. of ethanol
, and 480 ml. (5.8 moles) of 12N hydrochloric acid
. A white precipitate of ammonium chloride
forms within an hour. The reaction mixture is allowed to stand for 24 hours, and the precipitate is removed by suction filtration. The mother liquor is concentrated to a volume of 600 ml. (Note 3)
, and the precipitate (Note 4)
is removed by suction filtration. The mother liquor is evaporated to dryness (Note 5)
, and the residue is dissolved in 300 ml. of water. The solution is cooled in an ice bath
and made strongly alkaline (pH 13) with 6N sodium hydroxide
The two-phase mixture is placed in a separatory funnel
, and the heavy red-brown oil is separated. The aqueous phase is extracted with 100 ml. of ether
. The oil and the ether
extract are combined, washed with 50 ml. of saturated sodium chloride
, and dried over potassium carbonate
. The drying agent is removed by filtration, and the filtrate is distilled. Colorless 2-bromoallylamine
is collected at 65–68°/100 mm.; weight 49–59 g.
1.5075–1.5085 (Note 6)
The 2,3-dibromopropene was obtained from Columbia Organic Chemicals Co., Columbia, South Carolina
, and was redistilled before use. The preparation of 2,3-dibromopropene
is described in an earlier volume of this series.3
The submitters divided the mother liquor into 6 equal portions and concentrated each to a volume of 100 ml. at a pressure of 25 mm. in a 1-l. round-bottomed flask
on a rotary film evaporator. The rotary film evaporator used was obtained from Cenco Scientific Co., Santa Clara, California.
The submitters used a rotary film evaporator to evaporate the mother liquor at a pressure of 25 mm. in a water bath
heated to 90°.
discolors slowly even when stored at 0° in a dark container. The refractometer to be used for determination of the refractive index should be placed in a good hood
4. Merits of the Preparation
This method gives better yields than other methods of preparation of 2-bromoallylamine
, and it is the most convenient method for the preparation of large quantities of the compound. The procedure illustrates a reaction, the so-called Delépine reaction, that has been used for the preparation of many primary aliphatic amines.8,9,10,11,12,13
It is especially useful in the preparation of derivatives of phenacylamine
A number of primary aliphatic amines have been prepared by this method without isolation of the intermediate hexaminium salt.11
Several preparations of aliphatic aldehydes via the hexaminium salt have been described in earlier volumes of this series.17
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