Org. Synth. 1952, 32, 61
DOI: 10.15227/orgsyn.032.0061
asym-DIMETHYLUREA
[Urea, 1,1-dimethyl-]
Submitted by Frederick Kurzer
1
Checked by William S. Johnson and William T. Tsatsos.
1. Procedure
In a
1.5-l. beaker (Note 1),
191 ml. (180 g.) of aqueous 25% dimethylamine solution (1.0 mole) is diluted with 64 ml. of water and treated with
116 g. (1.1 moles) of nitrourea.
2 The temperature of the resulting brownish liquid rises spontaneously to 35–42°. The solution is warmed to 56–60°, and a reaction sets in vigorously with evolution of
nitrous oxide. External cooling with water is applied when required; the reaction temperature is maintained below 70° during the first 5–7 minutes and below 85° during the second period of 5–7 minutes. After a total of 10–15 minutes, the effervescence slackens and the reaction mixture is kept at 90–100° until the evolution of gas has completely ceased. This usually requires an additional 15–20 minutes.
The resulting liquid is heated with about 1 g. of activated carbon and is filtered with suction while hot; the clear, faintly colored filtrate is transferred to an evaporating dish and heated on a steam bath to remove most of the water. The residual, somewhat viscous, liquid (about 120 ml.) is then transferred to a beaker; the evaporating dish is rinsed with 10 ml. of water, and this solution is added to the contents of the beaker. To this is added 95% ethanol (50 ml.), and the mixture is warmed to effect solution. On cooling, large crystals separate which, at 0°, almost fill the bulk of the solution. The crystalline mass is broken up with a glass rod, collected on a suction filter, and washed quickly, while on the filter, with two successive portions of ice water (Note 2), drained, and air-dried (Note 3). The yield of large, colorless prismatic crystals of asym-dimethylurea is 35–40 g. (40–45%); m.p. 182–184° (Note 4).
The combined filtrates, on further evaporation and dilution with 95% ethanol as above, yield an additional 15–20 g. of material of approximately the same quality, bringing the total yield up to 57–68%. In a series of preparations, yields can be further increased a few per cent by carrying over mother liquors to subsequent batches.
2. Notes
1.
The reaction mixture froths considerably in the initial stages, and the use of a sufficiently large reaction vessel is important.
2.
Since
asym-dimethylurea is appreciably soluble in water, enough ice water is added to just cover the crystals on the filter, and suction is applied immediately.
3.
A slight odor of
dimethylamine, which persists, disappears when the product is dried at 80° for 1–2 hours.
4.
The use of
nitrourea is generally applicable to the preparation of
urea derivatives and usually affords the required
carbamide in excellent yield.
3,4
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3. Discussion
asym-Dimethylurea has been prepared by the interaction of
dimethylamine sulfate and
potassium cyanate5 or
dimethylamine and
nitrourea.
3 It is also obtained by the hydrolysis of
dimethylcyanamide in acid
6 and alkaline
7 media. Other reactions yielding the product include the action of
dimethylamine on
methyl γ-methylallophanate8 or
diethoxymethyleneimine,
9 and the hydrolysis of
1,1,2-trimethylisourea10 or
methyl dimethylthiocarbamate.
11
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
asym-DIMETHYLUREA
ethanol (64-17-5)
carbon (7782-42-5)
urea,
carbamide (57-13-6)
dimethylamine (124-40-3)
Nitrourea (556-89-8)
potassium cyanate (590-28-3)
dimethylcyanamide (1467-79-4)
Urea, 1,1-dimethyl- (598-94-7)
nitrous oxide (10024-97-2)
dimethylamine sulfate
methyl γ-methylallophanate
diethoxymethyleneimine
1,1,2-trimethylisourea
methyl dimethylthiocarbamate (16703-45-0)
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