Hexamethylphosphoramide

chembox
| Verifiedfields = changed
| verifiedrevid = 477494699
| Name = Hexamethylphosphoramide
| ImageFile = HMPA 2D skeletal. png
| ImageName = Chemical structure of HMPA
| ImageFile1 = Hexamethylphosphoramide from xtal 3D balls. png
| ImageName1 = 3D stick model of HMPA
| PIN = Hexamethylphosphoric triamide
| OtherNames = Hexamethylphosphoramide, Hexametapol, HMPA, Phosphoric tris(dimethylamide), HMPT
|Section1=
|Section2=Chembox Properties
| C=6 | H=18 | N=3 | O=1 | P=1
| MolarMass = 179.20 g/mol
| Density = 1.03 g/cm3
| MeltingPtC = 7.20
| BoilingPtC = 232.5
| BoilingPt notes = CRC
| Appearance = clear, colorless liquid
| PEL = none 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.

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.