Org. Synth. 1927, 7, 54
DOI: 10.15227/orgsyn.007.0054
[Hydracrylic acid]
Submitted by R. R. Read
Checked by H. T. Clarke and C. R. Nollep.
1. Procedure
To a cold solution of 160 g. (4 moles) of sodium hydroxide in 500 cc. of water in a 2-l. round-bottomed flask provided with a mechanical stirrer is added slowly 250 g. (3.5 moles) of ethylene cyanohydrin (p. 256), the temperature being kept below 30° (Note 1) by means of a cold water bath. The mixture is allowed to stand overnight in the bath, when the flask is fitted with a two-holed rubber stopper bearing a capillary tube reaching almost to the bottom and a delivery tube bent slightly downward for attachment to a suction pump. The flask is then heated slowly to 80° during four hours by raising the temperature of the surrounding water. A rapid current of air is drawn through the mixture during the heating. The mixture is now evaporated to dryness under reduced pressure by heating in an oil bath, the temperature of which is raised as rapidly as the boiling of the material will permit. The oil bath is finally held at 125° until the product becomes pasty. The flask is allowed to cool, and 50 cc. of water is poured down one side of the flask, and the solid material at that point worked carefully into a paste with a stout stirring rod.
A cooled mixture of 200 g. (109 cc.) of concentrated sulfuric acid (2 moles) and 300 cc. of water is now added slowly with careful cooling (Note 2), the pasty mixture being stirred with a thermometer and the temperature not being allowed to rise above 35°. Sodium sulfate crystallizes during this addition. The mass is now shaken vigorously with 400 cc. of ether and allowed to stand for some minutes. The ether is then decanted as completely as possible and the residue filtered with suction. The sodium sulfate is now shaken with six successive 300-cc. portions of ether, the ether solutions being subsequently employed for extraction of the filtrate. This latter requires 10–14 such extractions (each with 300–400 cc. of ether) for the satisfactory extraction of the β-hydroxypropionic acid. The combined ethereal solution is dried over 50 g. of anhydrous sodium sulfate and the ether distilled from a water bath, the temperature of which is not allowed to rise above 50°. The product is then concentrated under reduced pressure from a water bath maintained at 55–60°. The residue should have attained constant weight after four to six hours of this treatment; it consists of a sirupy liquid of pale straw color which contains 75–80 per cent of β-hydroxypropionic acid (by titration) (Note 3). The yield is 120–125 g. (28–31 per cent of the theoretical amount).
2. Notes
1. If the temperature of the mixture of nitrile and sodium hydroxide is allowed to rise too soon or too rapidly, the evolution of ammonia may become almost explosive, as the reaction is strongly exothermic.
2. The temperature during the addition of the sulfuric acid must be carefully controlled, as the heat of neutralization is sufficient to decompose the product. The use of a minimum amount of water is desirable in order to decrease the number of extractions.
3. β-Hydroxypropionic acid is an uncrystallizable and hygroscopic sirup. The 20–25 per cent of impurity remaining in the final product is largely water.
3. Discussion
β-Hydroxypropionic acid can be prepared by the hydrolysis of β-bromopropionic acid;1 by the action of alkali on acrylic acid;2 and by the hydrolysis of ethylene cyanohydrin with acid3 or preferably with alkali.4

References and Notes
  1. Lossen, Ann. 342, 128 (1905).
  2. Linnemann, Ber. 8, 1095 (1875); Erlenmeyer, Ann. 191, 281 (1878).
  3. Erlenmeyer, Ann. 191, 269 (1878).
  4. Wislicenus, Ann. 128, 6 (1863).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sulfuric acid (7664-93-9)

ammonia (7664-41-7)

ether (60-29-7)

sodium hydroxide (1310-73-2)

sodium sulfate (7757-82-6)

β-Bromopropionic acid (590-92-1)

Ethylene cyanohydrin (109-78-4)

Acrylic acid (9003-01-4)

hydracrylic acid,
β-Hydroxypropionic acid (503-66-2)