What are aldehydes?

Aldehydes are organic compounds that contain a carbonyl group (C=O) in which the carbon atom is bonded to at least one hydrogen atom. They occur both naturally and synthetically and play an important role in the chemical industry, e.g., in the manufacture of resins, dyes, solvents, and plastics. Some aldehydes, such as formaldehyde, are widely used intermediates in plastics and wood processing, while others, such as benzaldehyde, are found as flavorings in food.

Formation

Industrially, aldehydes are often produced by controlled oxidation of alcohols or by hydroformylation of alkenes. Formaldehyde is produced, for example, by catalytic oxidation of methanol, acetaldehyde by oxidation of ethanol or by hydration of acetylene. In nature, aldehydes are produced, among other things, by the oxidation of sugar or by enzymatic processes in plants and microorganisms.

Recognition

Aldehydes are mostly colorless liquids or gases with a characteristic, often pungent or aromatic odor. Formaldehyde has a sharp, pungent odor, while benzaldehyde has a pleasant almond-like smell. Many aldehydes are volatile and can be detected even in very low concentrations. They are reactive and tend to react with oxygen, water, or other compounds, which makes their storage and handling challenging.

Limit values

The occupational exposure limits for aldehydes depend heavily on the specific substance. For formaldehyde, an OEL of 0.37 mg/m³ (0.3 ppm) applies in the EU as a short-term value. Acetaldehyde has an OEL of 45 mg/m³ (25 ppm). Due to their harmful properties, many aldehydes are subject to strict legal limits, which are specified in the Technical Instructions on Air Quality Control (TA-Luft) and the Technical Rules for Hazardous Substances (TRGS).

Hazards

Aldehydes can be irritating to highly toxic. Formaldehyde is carcinogenic and can irritate the eyes, skin, and respiratory tract even in small amounts. Acetaldehyde is also irritating and is suspected of being carcinogenic. Some aldehydes, such as glutaraldehyde, have a strong disinfecting effect, but are also skin sensitizers and can cause breathing difficulties. In the environment, aldehydes can trigger photochemical reactions and contribute to the formation of ground-level ozone.