Checked by C. R. Noller and M. E. Synerholm.
1. Procedure
In a
5-l. round-bottomed flask,
500 g. (5.3 moles) of chloroacetic acid (Note
1) is dissolved in 700 cc. of water. The solution is warmed to 50°, neutralized with
290 g. (2.7 moles) of anhydrous sodium carbonate, and again cooled to room temperature. Meanwhile,
294 g. (6 moles) of sodium cyanide (97 per cent) is dissolved in 750 cc. of water warmed to 55°; the solution is cooled to room temperature and then added to the
sodium chloroacetate solution, with rapid mixing of the two solutions and cooling under the water tap. When the solutions are completely mixed, cooling is stopped and the temperature allowed to rise. When it reaches 95°, the solution is cooled by adding 200 cc. of ice water, and this is repeated, if necessary, until the temperature no longer rises (Note
2). The solution is then heated on the
steam bath for one hour to ensure completion of the reaction.
At the end of this time, the solution is cooled to room temperature and
240 g. (6 moles) of solid u.s.p. sodium hydroxide is slowly dissolved in it. When solution is complete, the reaction mixture is again heated on the steam bath under a hood. When the temperature reaches 60–70°, evolution of
ammonia begins and becomes more vigorous with rise in temperature. Most of the
ammonia is evolved in forty-five minutes, but the solution is heated for at least three hours, and the last traces of
ammonia are removed by bubbling steam through the hot solution for forty-five to sixty minutes more.
A solution of
600 g. of anhydrous calcium chloride in 1.8 l. of water warmed to 40° is added slowly with rapid mixing to the hot
sodium malonate solution. A cheese-like precipitate of
calcium malonate is formed immediately and becomes coarsely crystalline on standing for twenty-four hours. After the supernatant solution is decanted, the
calcium malonate is washed by decantation four or five times with 500-cc. portions of cold water. It is then transferred to a filter, sucked as dry as possible, and dried in the air, or at 45–50°, to constant weight. The yield is
800–900 g.
The dry
calcium malonate is placed in a
3-l. round-bottomed flask with sufficient
(750–1000 cc.) alcohol-free ether (Note
3) to make a paste which can be stirred. The flask is surrounded by an
ice bath, and the well-stirred salt is treated with
1 cc. of 12 N hydrochloric acid for each gram of salt. After the acid has been added slowly through a dropping funnel, the solution is transferred to a
continuous extractor (Note
4) and extracted with
ether until no more
malonic acid is obtained. The product, as obtained from the undried
ether solution by concentration, filtration, and drying in the air, melts at
130° or higher and is sufficiently pure for most purposes. The yield is
415–440 g. (
75–80 per cent of the theoretical amount).
2. Notes
1. A freshly distilled product boiling over a 3° range was used.
2. If the reaction between the cyanide and the chloroacetate becomes too vigorous,
hydrogen cyanide is liberated and partly changed to a brown material, and a corresponding quantity of glycolate is formed. If the temperature of the reaction mixture is allowed to go above 95° spontaneously, the liquid may boil so vigorously and suddenly as to escape from the flask despite the large extra volume provided.
3.
Ether is used to avoid unnecessarily increasing the volume of aqueous solution to be extracted. This
ether may be used for further extraction. It is necessary to use alcohol-free
ether to avoid esterifying the
malonic acid during the protracted extraction period.
4. A convenient type of extractor used in this preparation was made as follows by modifying that described by J. Friedrichs:
1 A
20-cm. calcium chloride tower, or other narrow-necked cylinder with a volume of about 1.3 l., was used as an extraction chamber. The mantle-tube, conducting the
ether vapors to an
Allihn condenser, was made of 25-mm. tubing and was about 50 cm. long. The goose-neck to the extraction flask, of 14-mm. tubing, was sealed to the mantle-tube about 8 cm. from the bottom end. The inner tube was of 14-mm. tubing, about 65 cm. long, flanged at the top to a diameter of about 20 mm. A
Witt filter plate of the proper diameter may be sealed into the bottom of the tube to make the
ether pass up through the water in a stream of fine bubbles, or this can also be accomplished by sealing off the bottom of the tube and piercing it with 3–6 pinholes. The mantle-tube was fitted to the chamber by a properly bored rubber stopper, the condenser to the top of the mantle-tube, and the 500-cc. extraction flask to the goose-neck by charred cork stoppers. With this apparatus
395–400 g. of
malonic acid was extracted in seventy-two hours, the
ether being changed every twenty-four hours, and the final traces were extracted after an additional twenty-four hours. The extractor as described by Friedrichs is shown in
.htmFig. 12.
Fig. 12
3. Discussion
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