Tetramethylurea

Tetramethylurea
Names
Other names
*TMU
Identifiers
632-22-4
ECHA InfoCard 100.010.159
PubChem 12437
Properties
C5H12N2O
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Tetramethylurea is a aprotic-polar solvent for organic compounds, especially for aromatic compounds and is used e. g. for Grignard reagents.[1]

The acute toxicity of tetramethylurea is moderate. However, it turned out to be embryotoxic and teratogenic towards several animal species[2] and should therefore be used under appropriate safety precautions.

Production

The synthesis and properties of tetramethylurea were comprehensively described by Arthur Lüttringhaus 1963.[1] The synthesis variant preferred by the authors is based on diphenyl carbonate (used for the preparation of polycarbonates) which is reacted with gaseous dimethylamine in an autoclave providing a yield of 74 %.

Tetramethylurea is formed in the reaction of dimethylcarbamoyl chloride with anhydrous sodium carbonate in a yield of 96.5%.[3]

Dimethylcarbamoyl chloride also reacts with excess dimethylamine forming tetramethylurea. Even though the product is contaminated and smelly it may be purified by addition of calcium oxide and subsequent fractional distillation.[4]

The reaction of dimethylamine with phosgene in the presence of e. g. 50 % sodium hydroxide solution and subsequent extraction with 1,2-dichloroethane yields tetramethylurea in 95% yield.[5]

The reactions with dimethylcarbamoyl chloride or phosgene are highly exothermic and the removal of the resulting dimethylamine hydrochloride requires some effort.[1]

Tetramethylurea is also formed during the oxidation of tetrakis(dimethylamino)ethylene (TDAE), a very electron-rich alkene[6] and a strong reducing agent, available from tris (dimethylamino) methane by pyrolysis[7] or from chlorotrifluoroethene and dimethylamine.[8]

TDAE reacts with oxygen in a (2+2) cycloaddition reaction to a 1,2-dioxetane which decomposes to electronically excited tetramethylurea. This returns to the ground state while emitting green light with an emission maximum at 515 nm.[9][10]

Properties

Tetramethylurea is a clear, colorless liquid with mild aromatic odor that is miscible with water and many organic solvents.[11] Unusual for an urea is the liquid state of tetramethylurea in a range of > 170 °C.

Applications

Tetramethylurea is miscible with a variety of organic compounds, including acids such as acetic acid or bases such as pyridine and an excellent solvent for organic substances such as ε-caprolactam or benzoic acid and dissolves even some inorganic salts such as silver nitrate or sodium iodide.[12][13] Due to its distinct solvent properties tetramethylurea is often used as a replacement for the carcinogenic hexamethylphosphoramide (HMPT).[14]

Tetramethylurea is suitable as a reaction medium for the polymerization of aromatic diacid chlorides (such as isophthalic acid) and aromatic diamines (such as 1,3-diaminobenzene(m-phenylenediamine)) to aramids such as poly (m-phenylene isophthalamide) (Nomex®)[15][16]

The polymerization of 4-amino benzoic acid chloride hydrochloride in tetramethylurea provides isotropic viscous solutions of poly(p-benzamide) (PPB), which can be directly spun into fibers.[17]

In a tetramethylurea-LiCl mixture stable isotropic solutions can be obtained up to a PPB polymer concentration of 14%.[18]

Tetramethylurea also dissolves cellulose ester and swells other polymers such as polycarbonates, polyvinyl chloride or aliphatic polyamides, usually at elevated temperature.[1]

Strong and hindered non-nucleophilic guanidine bases are accessible from tetramethylurea in a simple manner,[19][20] which are in contrast to the fused amidine bases DBN or DBU not alkylated.

A modification of the Koenigs-Knorr reaction for building glycosides from 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (acetobromoglucose) originates from S. Hanessian who used the silver salt silver trifluoromethanesulfonate (TfOAg) and as a proton acceptor tetramethylurea.[21] This process variant is characterized by a simplified process control, high anomeric purity and high yields of the products. If the reaction is carried out with acetobromoglucose and silver triflate/tetramethylurea at room temperature, then tetramethylurea reacts not only as a base, but also with the glycosyl to form a good isolable uroniumtriflats in 56% yield.[22]

References

  1. 1 2 3 4 A. Lüttringhaus; H.-W. Dirksen (1963), "Tetramethylharnstoff als Lösungsmittel und Reaktionspartner" (in German), Angew. Chem. 75 (22): pp. 1059–1068, doi:10.1002/ange.19630752204
  2. ↑ The MAK Collection for Occupational Health and Safety (2012) (in German), Tetramethylharnstoff [MAK Value Documentation in German language, 1979, Documentations and Methods], Weinheim: Wiley-VCH, doi:10.1002/3527600418.mb63222d0007, http://onlinelibrary.wiley.com/doi/10.1002/3527600418.mb63222d0007/full
  3. ↑ J.K. Lawson Jr.; J.A.T. Croom (1963), "Dimethylamides from alkali carboxylates and dimethylcarbamoyl chloride" (in German), J. Org. Chem. 28 (1): pp. 232–235, doi:10.1021/jo1036a513
  4. ↑ US 3597478, "Preparation of tetramethylurea"
  5. ↑ US 3681457, "Method of making tetramethylurea"
  6. ↑ H. Bock; H. Borrmann; Z. Havlas; H. Oberhammer; K. Ruppert; A. Simon (1991), "Tetrakis(dimethylamino)ethen: Ein extrem elektronenreiches Molekül mit ungewöhnlicher Struktur sowohl im Festkörper als auch in der Gasphase" (in German), Angew. Chem. 103 (12): pp. 1733–1735, doi:10.1002/ange.19911031246
  7. ↑ H. Weingarten; W.A. White (1966), "Synthesis of Tetrakis(dimethylamino)ethylene" (in German), J. Org. Chem. 31 (10): pp. 3427–3428, doi:10.1021/jo01348a520
  8. ↑ US 3293299, "Process for making tetrakis(dimethylamino)ethylene"
  9. ↑ H.E. Winberg; J.R. Downing; D.D. Coffman (1965), "The chemiluminescence of tetrakis(dimethylamino)ethylene" (in German), J. Am. Chem. Soc. 87 (9): pp. 2054–2055, doi:10.1021/ja01087a039
  10. ↑ "Chemilumineszenz von TDAE" (in German). illumina-chemie.de. 2014-08-08. Retrieved 2016-08-22.
  11. ↑ R.M. Giuliano (2004), (in German)e-EROS Encyclopedia of Reagents for Organic Synthesis, doi:10.1002/047084289X.rn00399
  12. ↑ B.J. Barker; J.A. Caruso (1976) (in German), The Chemistry of Nonaqueous Solvents, IV. Solution Phenomena and Aprotic Solvents, New York: Academic Press, pp. 110–127, ISBN 0-12-433804-6
  13. ↑ B.J. Barker; J. Rosenfarb; J.A. Caruso (1979), "Harnstoffe als Lösungsmittel in der chemischen Forschung" (in German), Angew. Chem. 91 (7): pp. 560–564, doi:10.1002/ange.19790910707
  14. ↑ A.J. Chalk (1970), "The use of sodium hydride as a reducing agent in nitrogen-containing solvents I. The reduction of chlorosilanes in Hexaalkylphosphoric triamides and tetraalkylureas" (in German), J. Organomet. Chem. 21 (1): pp. 95–101, doi:10.1016/S0022-328X(00)90598-9
  15. ↑ G. Odian (2004) (in German), Principles of Polymerization, 4th Edition, Hoboken, NJ: Wiley-Interscience, pp. 100, ISBN 0-471-27400-3
  16. ↑ H.G. Rodgers; R.A. Gaudiana; W.C. Hollinsed; P.S. Kalyanaraman; J.S. Manello; C. McGovern; R.A. Minns; R. Sahatjian (1985), "Highly amorphous, birefringent, para-linked aromatic polyamides" (in German), Macromolecules 18 (6): pp. 1058–1068, doi:10.1021/ma00148a003
  17. ↑ J. Preston (1978), A. Blumstein, ed. (in German), Synthesis and Properties of Rodlike Condensation Polymers, in Liquid Crystalline Order in Polymers, New York: Academic Press, pp. 141–166, ISBN 0-12-108650-X
  18. ↑ S.L. Kwolek; P.W. Morgan; J.R. Schaefgen; L.W. Gulrich (1977), "Synthesis, Anisotropic Solutions, and Fibers of Poly(1,4-benzamide)" (in German), Macromolecules 10 (6): pp. 1390–1396, doi:10.1021/ma60060a041
  19. ↑ Org. Synth. doi:10.15227/orgsyn.074.0101. Missing or empty |title= (help)
  20. ↑ D.H.R. Barton; J.D. Elliott; S.D. Géro (1981), "The synthesis and properties of a series of strong but hindered organic bases" (in German), J. Chem. Soc., Chem. Commun.: pp. 1136–1137, doi:10.1039/C39810001136
  21. ↑ S. Hanessian; J. Banoub (1977), "Chemistry of the glycosidic linkage. An efficient synthesis of 1,2-trans-disaccharides" (in German), Carbohydr. Res. 53: pp. C13–C16, doi:10.1016/S0008-6215(00)85468-3
  22. ↑ K. Bock; J. Fernández-Bolanos Guzmán; S. Refn (1992), "Synthesis and properties of 1,1,3,3-tetramethyl-2-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)uronium triflate" (in German), Carbohydr. Res. 232: pp. 353–357, doi:10.1016/0008-6215(92)80067-B
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