Organic Syntheses, CV 3, 71
Submitted by Anthony R. Ronzio and William B. Cook.
Checked by C. G. Stuckwisch and Henry Gilman.
1. Procedure
Seventy grams
(1 mole) of freshly prepared potassium methoxide (Note
1) and
41 g. (1 mole) of freshly purified acetonitrile (Note
2) are placed in a
500-ml. distilling flask. A
cold-finger condenser which extends into the bulb of the flask is inserted through a
rubber stopper in the neck of the flask, and a short piece of rubber tubing carrying a Hofmann clamp is connected to the side arm of the flask. The tubing is connected to an aspirator, and suction is applied until the
acetonitrile begins to boil, whereupon the tubing is closed by means of the clamp and the flask is heated for 5 hours in an
oil bath maintained at 140°.
At the end of the heating period the contents of the flask will have solidified. To the cold mixture 40 ml. of water is added to hydrolyze the
potassium methoxide and precipitate the
pyrimidine; the fine crystals are filtered and dried. The crude product is placed in a 500-ml. distilling flask with
250 ml. of purified kerosene (Note
3). On distilling the
kerosene, the
pyrimidine codistils and solidifies in the receiving flask to a snow-white mass of crystals. These are filtered, washed well with
petroleum ether, and dried in an
oven at 100°. The yield of pure material, melting at
182–183°, is
27.5–28.7 g. (
67–70%) (Note
4).
2. Notes
1. To prepare the
potassium methoxide 39 g. (1 gram atom) of metallic potassium, cut
under toluene (
Caution!) in 1-cm. cubes, is placed in a
1-l. three-necked flask which has been swept with
nitrogen. The flask, fitted with a
reflux condenser,
mechanical stirrer, and
dropping funnel, is immersed in a cooling bath at −30°, and absolute
methanol is added through the funnel until all the
potassium has dissolved. The excess
methanol is removed by heating on the steam bath, finally under reduced pressure, and the
potassium methoxide is dried overnight in a
vacuum desiccator over
sulfuric acid.
3.
Kerosene is purified by shaking for 24 hours with concentrated
sulfuric acid. The
kerosene is separated from the acid, washed several times with dilute
sodium hydroxide then with water, and finally dried over
calcium chloride and distilled using an air condenser. Purified
kerosene is a water-white, sweet-smelling liquid.
4. The percentage yield decreases when larger or smaller quantities of material are used.
3. Discussion
It has been reported that this trimerization may be carried out with equally good results through the use of a small amount of
sodium methoxide in place of a large amount of
potassium methoxide.
6
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved