Hexamethylphosphoramide, often abbreviated HMPA, is a
phosphoramide (an
amide of
phosphoric acid) with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
This colorless liquid is used as a solvent in
organic synthesis.
Structure and reactivity
HMPA is the oxide of
tris(dimethylamino)phosphine, P(NMe
2)
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
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
–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.
Applications
HMPA is a specialty
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
for
polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
s,
gases, and
organometallic compounds. It improves the selectivity of lithiation reactions by breaking up the
oligomers of
lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
bases such as
butyllithium. Because HMPA selectively solvates cations, it accelerates otherwise slow
SN2 reactions by generating more bare anions. The basic
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
centers in HMPA
coordinate strongly to Li
+.
HMPA is a ligand in the useful reagents based on
molybdenum
Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
peroxide complexes, for example, MoO(O
2)
2(HMPA)(H
2O) is used as an
oxidant
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ''electr ...
in organic synthesis.
Alternative reagents
Dimethyl sulfoxide can often be used in place of HMPA as a cosolvent. Both are strong
hydrogen bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...
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.
Toxicity
HMPA is only mildly toxic but has been shown to cause cancer in rats.
[ HMPA can be degraded by the action of hydrochloric acid.
]
References
External links
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{{Authority control
Phosphoramides
Solvents
IARC Group 2B carcinogens