(THF, oxacyclopentane, tetramethylene oxide)

CAS 109-99-9





Physical Properties

Colorless liquid

bp 66 °C, mp -108 °C

Miscible with water



Ethereal, detectable at 2 to 50 ppm


Vapor Density

2.5 (air = 1.0)


Vapor Pressure

160 mmHg at 25 °C


Flash Point

-14 °C


Autoignition Temperature

321 °C


Toxicity Data

LD50 oral (rat)

2880 mg/kg


LC50 inhal (rat)

21,000 ppm (3 h)



200 ppm (590 mg/m3)



200 ppm (590 mg/m3)



250 ppm (737 mg/m3)

Major Hazards

Highly flammable; forms sensitive peroxides on exposure to air, which may explode on concentration by distillation or drying.


The acute toxicity of THF by inhalation and ingestion is low. Liquid THF is a severe eye irritant and a mild skin irritant, but is not a skin sensitizer. At vapor levels of 100 to 200 ppm, THF irritates the eyes and upper respiratory tract. At high concentrations (25,000 ppm), THF vapor can produce anesthetic effects. Since the odor threshold for THF is well below the permissible exposure limit, this substance is regarded as having good warning properties.

Limited animal testing indicates that THF is not carcinogenic and shows developmental effects only at exposure levels producing other toxic effects in adult animals. Bacterial and mammalian cell culture studies demonstrate no mutagenic activity with THF.

Flammability and Explosibility

THF is extremely flammable (NFPA rating = 3), and its vapor can travel a considerable distance to an ignition source and "flash back." A 5% solution of THF in water is flammable. THF vapor forms explosive mixtures with air at concentrations of 2 to 12% (by volume). Carbon dioxide or dry chemical extinguishers should be used for THF fires.

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