Tetramethylurea

Tetramethylurea is the organic compound with the formula (Me2N)2CO. It is a substituted urea. This colorless liquid is used as an aprotic-polar solvent, especially for aromatic compounds and is used e. g. for Grignard reagents.[1]

Tetramethylurea
Names
Preferred IUPAC name
Tetramethylurea
Other names
1,1,3,3-Tetramethylurea
*TMU
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.010.159
EC Number
  • 211-173-9
UNII
  • InChI=1S/C5H12N2O/c1-6(2)5(8)7(3)4/h1-4H3
    Key: AVQQQNCBBIEMEU-UHFFFAOYSA-N
  • CN(C)C(=O)N(C)C
Properties
C5H12N2O
Molar mass 116.164 g·mol−1
Appearance Colorless liquid
Density 0.968 g/mL
Melting point −1.2 °C (29.8 °F; 271.9 K)
Boiling point 176.5 °C (349.7 °F; 449.6 K)
Hazards
GHS labelling:
GHS07: Exclamation markGHS08: Health hazard
Danger
H302, H360, H361
P201, P202, P264, P270, P281, P301+P312, P308+P313, P330, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Production

The synthesis and properties of tetramethylurea were comprehensively described.[1]

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.[2]

Synthesis of tetramethylurea from phosgene
Synthesis of tetramethylurea from phosgene

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

The reaction of diphenylcarbonate with dimethylamine in an autoclave is also effective.

Synthesis of tetramethylurea from diphenylcarbonate
Synthesis of tetramethylurea from diphenylcarbonate

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]

Synthesis of tetramethylurea from dimethylcarbamoyl chloride
Synthesis of tetramethylurea from dimethylcarbamoyl chloride

Tetramethylurea is also formed during the oxidation of tetrakis(dimethylamino)ethylene (TDAE), a very electron-rich alkene[5] and a strong reducing agent, available from tris(dimethylamino)methane by pyrolysis[6] or from chlorotrifluoroethene and dimethylamine.[7]

Synthesis of TDAE from chlorotrifluoroethene
Synthesis of TDAE from chlorotrifluoroethene

Tetrakis(dimethylamino)ethylene (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.[8][9]

Oxidation of TDAE (Chemiluminescence)
Oxidation of TDAE (Chemiluminescence)

Properties

Tetramethylurea is a clear, colorless liquid with mild aromatic odor that is miscible with water and many organic solvents.[10] 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.[11][12] Due to its distinct solvent properties tetramethylurea is often used as a replacement for the carcinogenic hexamethylphosphoramide (HMPT).[13]

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®)[14][15]

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.[16]

Polymerisation of p-Aminobenzoylchloride to PPB
Polymerisation of p-Aminobenzoylchloride to PPB

In a tetramethylurea-LiCl mixture stable isotropic solutions can be obtained up to a PPB polymer concentration of 14%.[17]

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,[18][19] which are in contrast to the fused amidine bases DBN or DBU not alkylated.

Synthesis of 2-tert.-Butyl-1,1,3,3-tetramethylguanidin aus TMU
Synthesis of 2-tert.-Butyl-1,1,3,3-tetramethylguanidin aus TMU

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.[20] 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 uroniumtriflates in 56% yield.[21]

Formation of Uronium salts with Acetobromoglucose and TMU
Formation of Uronium salts with Acetobromoglucose and TMU

Safety

The acute toxicity of tetramethylurea is moderate. However, it is embryotoxic and teratogenic towards several animal species.[22]


References
  1. A. Lüttringhaus; H.-W. Dirksen (1963), "Tetramethylharnstoff als Lösungsmittel und Reaktionspartner", Angew. Chem. (in German), vol. 75, no. 22, pp. 1059–1068, Bibcode:1963AngCh..75.1059L, doi:10.1002/ange.19630752204
  2. US 3681457, H. Babad, "Method of making tetramethylurea", published 1972-8-1, assigned to The Ott Chemical Co.
  3. J.K. Lawson Jr.; J.A.T. Croom (1963), "Dimethylamides from alkali carboxylates and dimethylcarbamoyl chloride", J. Org. Chem. (in German), vol. 28, no. 1, pp. 232–235, doi:10.1021/jo01036a513
  4. US 3597478, M.L. Weakly, "Preparation of tetramethylurea", published 1971-8-3, assigned to Nipak, Inc.
  5. 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", Angew. Chem. (in German), vol. 103, no. 12, pp. 1733–1735, Bibcode:1991AngCh.103.1733B, doi:10.1002/ange.19911031246
  6. H. Weingarten; W.A. White (1966), "Synthesis of Tetrakis(dimethylamino)ethylene", J. Org. Chem. (in German), vol. 31, no. 10, pp. 3427–3428, doi:10.1021/jo01348a520
  7. US 3293299, H. Boden, "Process for making tetrakis(dimethylamino)ethylene", published 1966-12-20, assigned to E.I. du Pont de Nemours and Co.
  8. H.E. Winberg; J.R. Downing; D.D. Coffman (1965), "The chemiluminescence of tetrakis(dimethylamino)ethylene", J. Am. Chem. Soc. (in German), vol. 87, no. 9, pp. 2054–2055, doi:10.1021/ja01087a039
  9. "Chemilumineszenz von TDAE" (in German). illumina-chemie.de. 2014-08-08. Retrieved 2016-08-22.
  10. R.M. Giuliano (2004). "Tetramethylurea". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00399. ISBN 978-0-471-93623-7.
  11. B.J. Barker; J.A. Caruso (1976), The Chemistry of Nonaqueous Solvents, IV. Solution Phenomena and Aprotic Solvents (in German), New York: Academic Press, pp. 110–127, ISBN 978-0-12-433804-3
  12. B.J. Barker; J. Rosenfarb; J.A. Caruso (1979), "Harnstoffe als Lösungsmittel in der chemischen Forschung", Angew. Chem. (in German), vol. 91, no. 7, pp. 560–564, Bibcode:1979AngCh..91..560B, doi:10.1002/ange.19790910707
  13. 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", J. Organomet. Chem. (in German), vol. 21, no. 1, pp. 95–101, doi:10.1016/S0022-328X(00)90598-9
  14. G. Odian (2004), Principles of Polymerization, 4th Edition (in German), Hoboken, NJ: Wiley-Interscience, p. 100, ISBN 978-0-471-27400-1
  15. 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", Macromolecules (in German), vol. 18, no. 6, pp. 1058–1068, Bibcode:1985MaMol..18.1058R, doi:10.1021/ma00148a003
  16. J. Preston (1978), A. Blumstein (ed.), Synthesis and Properties of Rodlike Condensation Polymers, in Liquid Crystalline Order in Polymers (in German), New York: Academic Press, pp. 141–166, ISBN 978-0-12-108650-3
  17. S.L. Kwolek; P.W. Morgan; J.R. Schaefgen; L.W. Gulrich (1977), "Synthesis, Anisotropic Solutions, and Fibers of Poly(1,4-benzamide)", Macromolecules (in German), vol. 10, no. 6, pp. 1390–1396, Bibcode:1977MaMol..10.1390K, doi:10.1021/ma60060a041
  18. D.H.R. Barton; M. Chen; J.C. Jászbérenyi; D.K. Taylor (1997). "Preparation and Reactions of 2-tert-butyl-1,1,3,3-tetramethylguanidine: 2,2,6-trimethylcyclohexen-1-yl iodide". Organic Syntheses. 74: 101. doi:10.15227/orgsyn.074.0101.
  19. D.H.R. Barton; J.D. Elliott; S.D. Géro (1981), "The synthesis and properties of a series of strong but hindered organic bases", J. Chem. Soc., Chem. Commun. (in German), no. 21, pp. 1136–1137, doi:10.1039/C39810001136
  20. S. Hanessian; J. Banoub (1977), "Chemistry of the glycosidic linkage. An efficient synthesis of 1,2-trans-disaccharides", Carbohydr. Res. (in German), vol. 53, pp. C13–C16, doi:10.1016/S0008-6215(00)85468-3
  21. 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", Carbohydr. Res. (in German), vol. 232, no. 2, pp. 353–357, doi:10.1016/0008-6215(92)80067-B
  22. The MAK Collection for Occupational Health and Safety (2012), "Tetramethylharnstoff [MAK Value Documentation in German language, 1979]", Tetramethylharnstoff [MAK Value Documentation in German language, 1979], Documentations and Methods (in German), Weinheim: Wiley-VCH, pp. 1–6, doi:10.1002/3527600418.mb63222d0007, ISBN 978-3-527-60041-0
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