Organic Syntheses, CV 3, 16
[I. BORON TRIFLUORIDE METHOD]
Submitted by C. E. Denoon, Jr.
Checked by Homer Adkins and Ivan A. Wolff.
1. Procedure
One hundred and sixteen grams (2 moles) of acetone (Note
1) and
510 g. (5 moles) of reagent grade acetic anhydride are placed in a
2-l. three-necked flask and cooled in an
ice-salt bath. One neck of the flask is stoppered; the second neck contains a tube for admitting
boron trifluoride; and the third neck contains an
outlet tube leading to an alkali trap to catch any unabsorbed
boron trifluoride. Commercial grade
boron trifluoride (Note
2) is passed through a
Kjeldahl bulb, to prevent the reaction mixture from sucking back into the cylinder, and is then bubbled into the reaction mixture at such a rate that 500 g. is absorbed in about 5 hours (2 bubbles per second). The reaction mixture is poured into a solution of
800 g. of hydrated sodium acetate in 1.6 l. of water contained in a
5-l. flask. The mixture is then steam-distilled and the distillate collected in the following portions: 1 l., 500 ml., 500 ml., 400 ml.
A solution of reagent grade hydrated
copper acetate is made by dissolving 240 g. of the salt in 3 l. of water at about 85° and filtering from any basic acetate. The
copper salt of acetylacetone is then precipitated by adding
1.4 l. of the hot copper acetate solution to the first fraction of the
acetylacetone, 700 ml. to the second, 500 ml. to the third, and 400 ml. to the fourth fraction. After standing for 3 hours, or better overnight, in a refrigerator the salt is filtered, washed once with water, and sucked dry. The salt is shaken in a
separatory funnel with
800 ml. of 20% sulfuric acid and
800 ml. of ether, and the
ether layer is removed. The aqueous layer is extracted with
400 ml. and then 200 ml. of ether. The combined extracts are dried with
250 g. of anhydrous sodium sulfate, and the
ether is removed by distillation. The residue is distilled through a
Widmer column (Note
3) and yields
160–170 g. of
acetylacetone boiling at
134–136° (
80–85% based on
acetone).
2. Notes
2.
Boron trifluoride may be purchased in cylinders from Harshaw Chemical Company, Cleveland, Ohio.
3. The
Widmer column used contained a spiral 15 cm. in length, 13 mm. in diameter, with 15 turns of the helix.
[II. SODIUM ETHOXIDE METHOD]
Submitted by Homer Adkins and James L. Rainey.
Checked by R. L. Shriner and Neil S. Moon.
1. Procedure
Sixty-nine grams (3 gram atoms) of sodium, from which all the oxide coating has been cut away, and
400 ml. of dry xylene (Note
1) are placed in a
1-l. round-bottomed flask and heated until the
sodium is melted. The flask is closed with a
rubber stopper (Note
2), and the
sodium is finely powdered by vigorous shaking. The contents of the flask are transferred to a
3-l. three-necked flask, and the
xylene decanted. The
sodium is washed with two
100-ml. portions of anhydrous ether (Note
3) by decantation. One liter of anhydrous
ether is added, and the flask is placed on a
steam bath and fitted with a
condenser,
Hershberg stirrer (Org. Syntheses, 17, 31), and a
250-ml. dropping funnel. The condenser and dropping funnel are protected by
drying tubes containing absorbent cotton (Note
4).
One hundred and thirty-eight grams (175 ml., 3 moles) of anhydrous ethanol is placed in the dropping funnel, and the stirrer is started. The alcohol is dropped in over a period of 2–3 hours with gentle refluxing. The reaction mixture is refluxed with stirring for 6 hours (Note
5) after the addition of the alcohol. The stirrer is stopped, the condenser turned downward, and the
ether distilled as completely as possible from the steam bath (Note
6).
The condenser is again arranged for refluxing, and
1.2 l. of ethyl acetate(Note
7) is added to the warm
sodium ethoxide through the separatory funnel as rapidly as possible. The stirrer is started immediately, and
174 g. (220 ml., 3 moles) of acetone (Note 1, p. 17) is dropped in over a period of 15–20 minutes, refluxing being maintained by heating if necessary. Addition of the
acetone must be started as soon as the
ethyl acetate has been added. During the addition the solution becomes quite red, and then the mixture turns brown (Note
8). The mixture is refluxed for 1 hour; the stirrer is then stopped and the contents of the flask are allowed to stand at room temperature for 12 hours, during which time crystals of the
sodium salt separate.
The liquid layer is decanted into a 5-l. flask, and the
sodium salt of the diketone is dissolved and washed into the flask with 2.5 l. of ice water. After the salt is dissolved, the ester layer is separated as soon as possible (Note
9). The water layer is extracted twice with
300-ml. portions of ether, and the
ether extract is discarded. To the water solution is added ice-cold dilute
sulfuric acid (150 g. of concentrated
sulfuric acid and 400 g. of cracked ice) until the solution is just acid to litmus. The diketone is extracted from the solution with four
300-ml. portions of ether. The combined
ether extracts are dried for 24 hours over
60 g. of anhydrous sodium sulfate in the
icebox. The
ether solution is decanted into a
2-l. round-bottomed flask, and the
sodium sulfate is extracted with
100 ml. of anhydrous ether. This extract is added to the
ether solution, and the
ether is distilled by means of a steam bath. The residue is transferred to a
500-ml. flask, rinsing with a little
ether, and distilled through a Widmer column, the portion boiling between 130° and 139° being collected. This fraction is dried over
5 g. of anhydrous potassium carbonate for 1 hour and, after the
carbonate has been removed, is redistilled through the Widmer column. The portion boiling at 134–136° is collected; it amounts to
115–136 g. (
38–45% based on
acetone).
2. Notes
2.
Rubber stoppers should be used throughout, including the drying of reagents, as corks contain some moisture. The stoppers should be boiled in
10% sodium hydroxide solution for 2 hours, thoroughly washed with dilute
acetic acid, and dried.
4. Absorbent cotton is an excellent drying agent and more convenient for drying tubes than anhydrous
calcium chloride.
2 It is possible to keep
maleic anhydride in a flask, closed only by a plug of absorbent cotton, for 3 weeks without appreciable change in the titration value (F. P. Pingert, private communication).
5. The period of heating varies somewhat with the size of the powdered
sodium. Almost all the
sodium should be used up before removal of the
ether. However, a few small pieces do no harm.
6. The success of the reaction depends upon the quality of the
sodium ethoxide used. The product at this point should be white and very finely divided. All moisture must be excluded during its preparation in order to avoid the formation of
sodium hydroxide, which markedly lowers the yield.
8. After about half of the
acetone has been added, the mixture usually sets to a solid mass. The stirrer is turned by hand and the addition of
acetone continued. In a few minutes the mass can again be stirred.
9. The
ethyl acetate layer is washed with water,
sodium bisulfite solution, saturated
calcium chloride solution, and again with water. It is further purified as in (Note
6), giving
316–400 g. of recovered ester. The amount of recovered ester depends somewhat upon the length of time the two layers are allowed to remain in contact before separating.
3. Discussion
This preparation is referenced from:
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved