Hexamethylphosphoramide

Chembox new
Name = Hexamethylphosphoramide
ImageFile = HMPA-2D-skeletal.png ImageName = Chemical structure of HMPA
ImageFile1 = HMPA-3D-sticks.png ImageName1 = 3D stick model of HMPA
IUPACName = Hexamethylphosphoramide
OtherNames = Hexametapol
HMPA

Section1 = Chembox Identifiers
CASNo = 680-31-9
SMILES = CN(C)P(=O)(N(C)C)N(C)C
Section2 = Chembox Properties
Formula = C₆H₁₈N₃OP
MolarMass = 179.20 g/mol
Density = 1.03 g/cm³
MeltingPt = 7.20 °C
BoilingPt = 235 °C

Hexamethylphosphoramide (abbreviated HMPA) is a colorless organic liquid with the formula [(CH₃)₂N] ₃PO.

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

Applications

HMPA is used as a polymer solvent, as a selective solvent for gases, stabilizer in polystyrene against thermal degradation, as a laboratory solvent for organometallic and in organic reactions. It has been tested as a fire retardant and as an insect chemosterilant, but there is no known current use of HMPA for these applications.

It is useful for improving the selectivity of certain organic reactions. For instance in some deprotonation reactions HMPA breaks up the oligomers of lithium bases such as butyllithium. Also because HMPA solvates cations so well, while not solvating anions, it has been used as a solvent for some difficult S_N2 reactions. The basic oxygen atom in HMPA coordinates strongly to lithium cation.Dykstra, R. R. "Hexamethylphosphoric Triamide" Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons, Ltd. DOI: 10.1002/047084289X.rh020] A molybdenum peroxide complex of HMPA is used in synthetic chemistry as an oxidant.

Alternative reagents

Dimethyl sulfoxide can often be used in place of HMPA as a solvent. Both are strong hydrogen bond acceptors, and their oxygen atoms are able to bind to metal cations. Other alternatives to HMPA include the tetraalkylureas [Beck, A. K.; Seebach, D. "N,N'-Dimethylpropyleneurea" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons, New York. DOI: 10.1002/047084289X.rd366.] and the cyclic alkylureas like DMPU. [cite journal
title = Substitution of HMPT by the cyclic urea DMPU as a cosolvent for highly reactive nucleophiles and bases
author = Triptikumar Mukhopadhyay, Dieter Seebach
journal = Helvetica Chimica Acta
volume = 65
issue = 1
pages = 385–391
year = 1982
url =
doi = 10.1002/hlca.19820650141]

Toxicity

HMPA is only mildly toxic but has been shown to cause nasal cancers in rats. HMPA can be degraded to less toxic compounds by the action of hydrochloric acid. In phosphorus chemistry it is the case in general that the treatment of a compound containing a nitrogen phosphorus single bond with hydrogen chloride will form a protonated amine and a "P"-chloro compound. For example if "P"-dimethylamino-"P, P"-diphenyl phosphine is treated with hydrogen chloride then "P"-chloro-"P, P"-diphenyl phosphine and dimethylamine HCl salt will be obtained.

References

*"Merck Index", 12th Edition, 4761.

External links

* [http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s095hexa.pdf The substance profile of HMPA in the report on carcinogens]