What are phenols?

Phenols are aromatic compounds that have a hydroxyl group (–OH) directly attached to an aromatic ring. This particular structure gives them both the properties of alcohols and the reactivity of aromatic systems. Phenols are widely used in the chemical industry, including as intermediates in the manufacture of plastics, resins, plasticizers, antioxidants, and pharmaceutical active ingredients.

Formation

Industrially, phenol is mainly produced using the cumene hydroperoxide process, in which cumene (isopropylbenzene) is oxidized to cumene hydroperoxide and then split into phenol and acetone. Other phenols are formed by hydrolysis of halogenated aromatic compounds under alkaline conditions or by extraction from coal tar. In nature, phenols occur in plants, where they serve as defensive substances and colorants, among other things.

Recognition

Phenols are usually colorless to pale pink, crystalline solids or oily liquids with a characteristic pungent to sweet odor. Many phenols are only moderately soluble in water, but highly soluble in organic solvents. They are weak acids and can form salts (phenolates) with bases. Phenols tend to oxidize when exposed to air, which can lead to a change in color.

Limit values

In the EU, the occupational exposure limit for phenol is 2 ppm (8 mg/m³). Cresols have limit values between 5 and 20 ppm, depending on the isomer. Due to the possibility of skin absorption, additional occupational safety measures apply to phenols, such as closed systems or protective gloves with high chemical resistance.

Hazards

Phenols are highly corrosive and can cause severe skin and eye damage even in small quantities. Upon skin contact, phenol is rapidly absorbed and can cause systemic poisoning, affecting the central nervous system, heart, and kidneys. Phenol vapors irritate the respiratory tract, and some substituted phenols are suspected of being carcinogenic. In the environment, phenols are toxic to aquatic organisms and can pollute ecosystems due to their persistence.