Hexamethylphosphoramide

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

Hexamethylphosphoramide

Chemical structure of HMPA
3D stick model of HMPA
Names
Preferred IUPAC name Hexamethylphosphoric triamide[1]
Other names Hexamethylphosphoramide Hexametapol HMPA Phosphoric tris(dimethylamide)[2] HMPT[3]
Identifiers
CAS Number	680-31-9 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1099903
ChEBI	CHEBI:24565 Y
ChEMBL	ChEMBL3187047
ChemSpider	12158 Y
ECHA InfoCard	100.010.595
EC Number	211-653-8
Gmelin Reference	3259
KEGG	C19250 Y
PubChem CID	12679
RTECS number	TD0875000
UNII	M42TU5843Z Y
UN number	2810 3082
CompTox Dashboard (EPA)	DTXSID6020694
InChI InChI=1S/C6H18N3OP/c1-7(2)11(10,8(3)4)9(5)6/h1-6H3 Y Key: GNOIPBMMFNIUFM-UHFFFAOYSA-N Y InChI=1/C6H18N3OP/c1-7(2)11(10,8(3)4)9(5)6/h1-6H3 Key: GNOIPBMMFNIUFM-UHFFFAOYAP
SMILES O=P(N(C)C)(N(C)C)N(C)C
Properties
Chemical formula	C6H18N3OP
Molar mass	179.20 g/mol
Appearance	colorless liquid[4]
Odor	aromatic, mild, amine-like[4]
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[5]
Solubility in water	miscible[4]
Vapor pressure	0.03 mmHg (4.0 Pa) at 20 °C[4]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Suspected Carcinogen[4]
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H340, H350
Precautionary statements	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)	none[4]
REL (Recommended)	Ca[4]
IDLH (Immediate danger)	Ca [N.D.][4]
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 YN ?) Infobox references

Structure and reactivity

HMPA is the oxide of 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^[6] and alkali metals, forming blue solutions which are stable for a few hours. Solvated electrons are present in these blue solutions.^[7]

Applications

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 S_N2 reactions by generating more bare anions. The basic nitrogen centers in HMPA coordinate strongly to Li⁺.^[8]

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.^[9]

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)^[10][11] or DMI (1,3-dimethyl-2-imidazolidinone).^[12] Tripyrrolidinophosphoric acid triamide (TPPA) has been reported to be a good substitute reagent for HMPA in reductions with samarium diiodide^[13] and as a Lewis base additive to many reactions involving samarium ketyls.^[14]

Toxicity

HMPA is only mildly toxic but has been shown to cause cancer in rats.^[8] HMPA can be degraded by the action of hydrochloric acid.