Hexamethylphosphoramide: Properties, Uses and Hazard

Properties of Hexamethylphosphoramide

Hexamethylphosphoramide (HMPA) is a clear colourless liquid with an aromatic odour. The chemical formula for HMPA is C6H18N3OP, and the molecular weight is 179.24 g/mol. The vapor pressure for HMPA is 0.07 mm Hg at 25 °C, and it has a log octanol/water partition coefficient (log K ow ) of 0.28.

When heated to decomposition, HMPA releases highly toxic fumes of phosphine, phosphorus oxides and nitrogen oxides. Compounds containing nitrogen-phosphorus bonds usually degrade in the presence of hydrochloric acid to form protonated amines and phosphates.HMPA dissolves alkali metals to form a blue solution of dissolved electrons, which is stable for several hours. Dimethyl sulfoxide can often be used as a cosolvent in place of HMPA. Both are strong hydrogen-bonded acceptors whose oxygen atoms are bound to metal cations.

Uses of Hexamethylphosphoramide

Hexamethylphosphoramide acts as a mutagen and insecticide. HMPA is used as a stabiliser against thermal degradation in polystyrene, as a selective solvent for gases, as a catalyst for polymerisation, as an additive to polyethylene and polyolefin resins to protect against ultraviolet degradation and as a solvent for organo- and organo-metallic reactions in research laboratories. HMPA is also used as a gas sensor for the detection of carcinogens.

Hazard of Hexamethylphosphoramide

Hexamethylphosphoramide is considered as one of the harmful of all carcinogens. Exposure to HMPA can irritate the eyes, skin and respiratory tract. Acute animal studies have reported effects on the kidneys and lungs from oral administration of HMPA, while chronic animal oral administration studies have reported an increased incidence of lung disease. Inhalation of HMPA has been reported to increase the incidence of nasal tumours in rats. HMPA has not been classified as a carcinogen by the U.S. EPA, but the International Agency for Research on Cancer (IARC) has classified HMPA as a probable human carcinogen in category 2B. NIOSH also considers HMPA a potential occupational carcinogen.

References:

[1] Hexamethylphosphoramide.[J]. Report on carcinogens : carcinogen profiles, 2020. DOI:10.32388/7r71kl. 

[2] DIPAK GORAKH BABAR. High sensitivity sensor development for Hexamethylphosphoramide by polyaniline coated polyurethane membrane using resistivity assessment technique[J]. Measurement, 2016. DOI:10.1016/j.measurement.2016.03.078.