Chemical structure of HMPA
3D stick model of HMPA
Preferred IUPAC name
Hexamethylphosphoric triamide
Other names
  • Hexamethylphosphoramide
  • Hexametapol
  • HMPA
  • Phosphoric tris(dimethylamide)
  • HMPT
3D model (JSmol)
ECHA InfoCard 100.010.595 Edit this at Wikidata
EC Number
  • 211-653-8
RTECS number
  • TD0875000
UN number 2810 3082
  • InChI=1S/C6H18N3OP/c1-7(2)11(10,8(3)4)9(5)6/h1-6H3 checkY
  • InChI=1/C6H18N3OP/c1-7(2)11(10,8(3)4)9(5)6/h1-6H3
  • O=P(N(C)C)(N(C)C)N(C)C
Molar mass 179.20 g/mol
Appearance clear, colorless liquid
Odor aromatic, mild, amine-like
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
Vapor pressure 0.03 mmHg (4.0 Pa) at 20 °C
Occupational safety and health (OHS/OSH):
Main hazards
Suspected Carcinogen
GHS labelling:
GHS08: Health hazard
H340, H350
P201, P202, P281, P308+P313, P405, P501
Flash point 104.4 °C (219.9 °F; 377.5 K)
NIOSH (US health exposure limits):
PEL (Permissible)
REL (Recommended)
IDLH (Immediate danger)
Ca [N.D.]
Safety data sheet (SDS) Oxford MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

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

Structure and reactivity

HMPA is the oxide tris(dimethylamino)phosphine, P(NMe2)3. Like other phosphine oxides (such as 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.

It dissolves alkali metal salts and alkali metals, forming blue solutions which are stable for a few hours. Solvated electrons are present in these blue solutions.


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 bare anions. The basic nitrogen centers in HMPA coordinate strongly to Li+.

HMPA is a ligand in the useful reagents based on molybdenum peroxide complexes, for example, MoO(O2)2(HMPA)(H2O) is used as an oxidant in organic synthesis.

Alternative reagents

Dimethyl sulfoxide can often be used in place of HMPA as a cosolvent. Both are strong hydrogen bond acceptors, and their oxygen atoms bind metal cations. Other alternatives to HMPA include the N,N′-tetraalkylureas DMPU (dimethylpropyleneurea) or DMI (1,3-dimethyl-2-imidazolidinone). Tripyrrolidinophosphoric acid triamide (TPPA) has been reported to be a good substitute reagent for HMPA in reductions with samarium diiodide and as a Lewis base additive to many reactions involving samarium ketyls.


HMPA is only mildly toxic but has been shown to cause cancer in rats. HMPA can be degraded by the action of hydrochloric acid.

This page was last updated at 2024-04-18 14:41 UTC. Update now. View original page.

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