From Wikipedia, the free encyclopedia
Jump to: navigation, search
Chemical structure of HMPA
3D stick model of HMPA
IUPAC name
Preferred IUPAC name
Hexamethylphosphoric triamide
Other names
Phosphoric tris(dimethylamide)
3D model (JSmol)
ECHA InfoCard 100.010.595
Molar mass 179.20 g/mol
Appearance clear, colorless liquid[1]
Odor aromatic, mild, amine-like[1]
Density 1.03 g/cm3
Melting point 7.20 °C (44.96 °F; 280.35 K)
Boiling point 232.5 °C (450.5 °F; 505.6 K) CRC[2]
Vapor pressure 0.03 mmHg (20°C)[1]
Main hazards carcinogen[1]
Safety data sheet Oxford MSDS
Toxic T
Flash point 104.4 °C (219.9 °F; 377.5 K)
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
IDLH (Immediate danger)
Ca [N.D.][1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (i.e. an amide of phosphoric acid) with the formula [(CH3)2N]3PO. This colorless liquid is a useful polar aprotic solvent and additive in organic synthesis.

Structure and reactivity[edit]

HMPA is the oxide of the highly basic tertiary phosphine hexamethylphosphorous triamide (HMPT[3]), P(NMe2)3. Like other phosphine oxides (e.g., triphenylphosphine oxide), the molecule has a tetrahedral core and a P-O bond that is highly polarized, with significant negative charge residing on the oxygen atom.

Compounds containing a nitrogen-phosphorus bond typically are degraded by hydrochloric acid to form a protonated amine and phosphate.


HMPA is a specialty solvent for polymers, gases, and organometallic compounds. It improves the selectivity of lithiation reactions by breaking up the oligomers of lithium bases such as butyllithium. Because HMPA selectively solvates cations, it accelerates otherwise slow SN2 reactions by generating more "naked" anions. The basic nitrogen centers in HMPA coordinate strongly to Li+.[4]

HMPA is a ligand in the useful reagents based on molybdenum peroxide complexes, e.g., MoO(O2)2(HMPA)(H2O) is used as an oxidant in organic synthesis.[5]

Alternative reagents[edit]

Dimethyl sulfoxide can often be used in place of HMPA as a solvent. Both are strong hydrogen bond acceptors, and their oxygen atoms bind metal cations. Other alternatives to HMPA include the tetraalkylureas[6] and the cyclic alkylureas like DMPU.[7]


HMPA is only mildly toxic but has been shown to cause nasal cancers in rats.[4] Still, many organic chemists regard HMPA as an exceptionally hazardous molecule due to its known carcinogenicity, and avoid its use when possible. HMPA can be degraded to less toxic compounds by the action of hydrochloric acid. For laboratory uses it can be substituted by the less carcinogenic solvent DMI (1,3-Dimethyl-2-imidazolidinone).[8]


  1. ^ a b c d e f g h "NIOSH Pocket Guide to Chemical Hazards #0321". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Haynes, William M. (2010). Handbook of Chemistry and Physics (91 ed.). Boca Raton, Florida: CRC Press. p. 3-280. ISBN 978-1439820773. 
  3. ^ Confusingly, some sources (e.g., e-EROS) list HMPT as an abbreviation for O=P(NMe2)3 (hexamethylphosphoric triamide), as well as an abbreviation for P(NMe2)3 (hexamethylphosphorous triamide).
  4. ^ a b Dykstra, R. R. (2001). "Hexamethylphosphoric Triamide". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rh020. 
  5. ^ Dickman, Michael H.; Pope, Michael T. (1994). "Peroxo and Superoxo Complexes of Chromium, Molybdenum, and Tungsten". Chemical Reviews. 94: 569–84. doi:10.1021/cr00027a002. 
  6. ^ Beck, A. K.; Seebach, D. (2001). "N,N'-Dimethylpropyleneurea". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rd366. 
  7. ^ Mukhopadhyay, T.; Seebach, D. (1982). "Substitution of HMPT by the Cyclic Urea DMPU as a Cosolvent for highly Reactive Nucleophiles and Bases". Helvetica Chimica Acta. 65 (1): 385–391. doi:10.1002/hlca.19820650141. 
  8. ^ Lo, C. C.; Chao, P. M. (1992). "Replacement of Carcinogenic Solvent HMPA by DMI in Insect Sex Pheromone Synthesis" (pdf). Journal of Chemical Ecology. 18 (2): 3245–3253. doi:10.1007/BF00982095. 

External links[edit]

  • "Hexamethylphosphoramide CAS No. 680-31-9" (pdf). Report on Carcinogens, Twelfth Edition. National Toxicology Program, Department of Health and Human Services. 2011. 
  • "Hexamethyl phosphoramide". NIOSH Pocket Guide to Chemical Hazards. Centers for Disease Control and Prevention, Department of Health and Human Services. 2011. 
  • Merck Index, 12th Edition, 4761.