Appearance Colourless gas Molar mass 42.04 g/mol Melting point -150.5 °C | Formula C2H2O Boiling point -56.1 °C Classification Volatile organic compound | |
Ethenone is the formal name for ketene, an organic compound with formula C2H2O or H2C=C=O. It is the simplest member of the ketene class. It is a tautomer of ethynol.
Contents
Properties
Ethenone is a very poisonous colourless gas at STP and has a sharp irritating odour. It is soluble in acetone, ethanol, ethyl ether, aromatic solvents and halocarbons.
Preparation
Ethenone can be prepared in the laboratory by pyrolysis of acetone vapor. It is also formed by reacting acetyl chloride with a proton acceptor like trimethylamine.
Reactions
Ethenone is very reactive, tending to react with nucleophiles to form an acetyl group. For example, it reacts with water to form acetic acid; with acetic acid to form acetic anhydride; with ammonia and amines to form ethanamides; and with dry hydrogen halides to form acetyl halides.
Ethenone will also react with itself via 2+2 photocycloaddition to form cyclic dimers known as diketenes. For this reason, it should not be stored for long periods.
Hazards
Exposure to concentrated levels causes humans to experience irritation of body parts such as the eye, nose, throat and lungs. Extended toxicity testing on mice, rats, guinea pigs and rabbits showed that ten-minute exposures to concentrations of freshly generated ethenone as low as 0.2 mg/liter (116 ppm) may produce a high percentage of deaths in small animals. These findings put ethenone in the same order of toxicity as phosgene (0.2–20 mg/liter) and hydrogen cyanide (0.2-0.5 mg/liter). Death is from pulmonary edema and is entirely similar to, but much more rapid than is the case with phosgene poisoning.
Occupational exposure limits are set at 0.5 ppm (0.9 mg/m3) over an eight-hour time-weighted average. An IDLH limit is set at 5 ppm, as this is the lowest concentration productive of a clinically relevant physiologic response in humans.