What are ketones?

Ketones are organic compounds that contain a carbonyl group (C=O) between two carbon atoms. They are among the simpler organic oxygen compounds and occur both naturally and synthetically. Ketones are used in a variety of industrial processes—particularly as solvents, starting materials for plastics and resins, and in the pharmaceutical, paint, and adhesive industries.

Formation

Industrially, ketones are often produced by the oxidation of secondary alcohols. Acetone, for example, is produced as a by-product of phenol production (cumene hydroperoxide process) or by catalytic dehydrogenation of isopropanol. Methyl ethyl ketone (MEK) is produced by dehydrogenation of 2-butanol, while cyclohexanone is obtained by oxidation of cyclohexane or dehydrogenation of cyclohexanol. Some ketones are also produced as by-products of fermentation and biochemical processes.

Detection

Ketones are usually colorless liquids with a characteristic, often sweetish-pungent odor. Many ketones are volatile and highly flammable, requiring special care in storage and handling. They are readily miscible with many organic solvents, and some, such as acetone, are also completely miscible with water. Due to their low viscosity and high volatility, ketones evaporate quickly at room temperature and are often detectable by smell even at low concentrations.

Limit values

Occupational exposure limits vary depending on the ketone. For acetone, the OEL in the EU is 500 ppm (1200 mg/m³), for MEK it is 200 ppm (600 mg/m³), and for cyclohexanone it is 10 ppm (40 mg/m³). These values apply to an average exposure time of eight hours and are intended to prevent health problems.

Hazards

Ketones irritate the eyes and respiratory tract and, in high concentrations, can cause headaches, dizziness, and lightheadedness. Some ketones, such as cyclohexanone, can also cause skin irritation. If handled improperly, there is also a risk of fire and explosion due to their high flammability. Many ketones are readily biodegradable in the environment, but can harm aquatic organisms at high concentrations.