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Org. Synth. 1952, 32, 61
DOI: 10.15227/orgsyn.032.0061
asym-DIMETHYLUREA
[Urea, 1,1-dimethyl-]
Submitted by Frederick Kurzer1
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
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 acid6 and alkaline7 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

References and Notes
  1. School of Medicine, University of London, London, England.
  2. Org. Syntheses Coll. Vol. 1, 417 (1941).
  3. Davis and Blanchard, J. Am. Chem. Soc., 51, 1798 (1929).
  4. Buck and Ferry, J. Am. Chem. Soc., 58, 854 (1936).
  5. Franchimont, Rec. trav. chim., 2, 122 (1883); 3, 222 (1884).
  6. Diels and Gollmann, Ber., 44, 3165 (1911).
  7. von Braun and Röver, Ber., 36, 1197 (1903).
  8. Biltz and Jeltsch, Ber., 56, 1920 (1923).
  9. Schenck, Arch. Pharm., 249, 467 (1911); Z. physiol. Chem., 77, 368 (1912).
  10. McKee, Am. Chem. J., 42, 25 (1909).
  11. Delepine and Schving, Bull. soc. chim. France, [4] 7, 900 (1910).

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)