Org. Synth. 1956, 36, 23
DOI: 10.15227/orgsyn.036.0023
N,N-DIMETHYLSELENOUREA
[Urea, 1,1-dimethyl-2-seleno-]
Submitted by Frank Bennett and Ralph Zingaro
1.
Checked by C. F. H. Allen and K. C. Kennard.
1. Procedure
Caution! Hydrogen selenide is very toxic. This preparation should be carried out in a well-ventilated hood. The operator should wear rubber gloves. The apparatus should be screened from bright light.
A mixture of 37 g. (0.5 mole) of dimethylcyanamide (Note 1), 75 ml. of concentrated ammonium hydroxide, and 25 ml. of water is placed in a 250-ml. round-bottomed three-necked flask fitted with a stirrer, thermometer, and glass delivery tube (Note 2). The solution is stirred slowly, while hydrogen selenide (Note 3) is slowly bubbled in, maintaining the temperature at 20–30° by occasional external cooling. At the end of the reaction (4–5 hours) when there is no more gas evolution from the generator (4–5 hours), the flask and contents are cooled to 5–10° and stirred vigorously for one-half hour. The solid is then collected on a 9-cm. Büchner funnel and washed with 250 ml. of ice-cold 95% ethanol. The crude, gray product weighs 65–73 g. (81–91%).
For purification, it is dissolved in 9–9.5 l. of boiling benzene (Note 4). The solution is filtered rapidly, using a 32-cm. folded filter in an 8-in. short-stem glass funnel. The recovery is 59–70 g. The fine, white crystals, which melt at 169–170° (Note 5), are stored in a brown glass bottle under nitrogen (Note 6), (Note 7), (Note 8).
2. Notes
1.
The
practical grade, b.p. 162–164°, obtained from the Eastman Kodak Company, was used.
2.
A tube 8 mm. in diameter is used. A sintered-glass gas addition tube is quickly clogged by
selenium.
3.
Hydrogen selenide is generated from
iron or
aluminum selenide and a mineral acid. In a
2-l. three-necked, flask, fitted with sealed stirrer,
reflux condenser, and
dropping funnel are placed
135 g. (1 mole) of powdered iron selenide (Note 9) and 350 ml. of water. The generator is heated on a steam cone, while
350 ml. of concentrated hydrochloric acid is admitted slowly with stirring, so that the
hydrogen selenide is evolved at a steady rate. (The generation of gas is regulated both by the rate of heating and the rate of addition of acid, so that the gas is absorbed almost entirely; it is led from the top of the condenser to the delivery tube.) The amount of selenide used is sufficient. The residual liquid in the generator is left open to the air overnight in a hood. Then sufficient
50% sodium hydroxide solution is added to make it basic, and the whole is flushed down the sink, using a large amount of water.
4.
Recrystallization from
benzene affords a product that has superior storage qualities. A liter dissolves 5–6 g. at the boiling point.
5.
The melting point is unchanged by further recrystallization.
6.
The product turns pink, and eventually gray, if exposed to air for an extended period. It should be stored under
nitrogen.
27.
The submitters indicate that
N,N-diethylselenourea may be prepared similarly, using
diethylcyanamide. In this case, a solution of
50 ml. each of concentrated aqueous ammonium hydroxide and
ethanol is used as a solvent. The reaction is carried out at 60°, the solvent being replenished as needed by a solution containing
80 ml. of ethanol and
20 ml. of concentrated ammonium hydroxide. The yield of crude material is
65–80%. Recrystallization from
benzene gives a white product, m.p.
117–118°.8.
The procedure gives a commensurate yield when carried out on twice the scale.
9.
Iron selenide can be obtained from the Canadian Copper Refiners Ltd., Montreal, Quebec.
3. Discussion
The procedure used is that of Zingaro, Bennett, and Hammar.
2
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethanol (64-17-5)
hydrochloric acid (7647-01-0)
Benzene (71-43-2)
sodium hydroxide (1310-73-2)
iron (7439-89-6)
nitrogen (7727-37-9)
ammonium hydroxide (1336-21-6)
selenium
hydrogen selenide (7782-49-2)
N,N-Dimethylselenourea,
Urea, 1,1-dimethyl-2-seleno- (5117-16-8)
dimethylcyanamide (1467-79-4)
aluminum selenide (1302-82-5)
iron selenide
N,N-diethylselenourea (15909-81-6)
diethylcyanamide (617-83-4)
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