Phenols

Salicylic-acid-skeletal.svg

Phenols are a class of chemical compounds consisting of a hydroxyl group (-OH) directly bonded to an aromatic hydrocarbon group. The simplest of the class is phenol (C6H5OH), also known as carbolic acid. Phenols are distinct from alcohols in that the hydroxyl group is directly connected to an aromatic ring, which significantly alters the properties of the compound.

Structure and Properties

Phenols are characterized by the presence of a hydroxyl group attached to an aromatic ring. This structure imparts unique properties to phenols, such as increased acidity compared to alcohols. The aromatic ring allows for resonance stabilization of the negative charge on the oxygen atom when the hydrogen ion is lost, making phenols more acidic.

Synthesis

Phenols can be synthesized through several methods, including:

• The cumene process, which involves the oxidation of cumene to cumene hydroperoxide, followed by acid-catalyzed cleavage to yield phenol and acetone.
• The Raschig-Hooker process, which involves the hydrolysis of chlorobenzene.
• The Kolbe-Schmitt reaction, which involves the carboxylation of sodium phenoxide followed by acidification to yield salicylic acid, a precursor to phenol.

Reactions

Phenols undergo a variety of chemical reactions, including:

• Electrophilic aromatic substitution, where the hydroxyl group activates the aromatic ring towards substitution reactions.
• Oxidation, where phenols can be oxidized to quinones.
• Esterification, where phenols react with carboxylic acids or acid anhydrides to form esters.

Applications

Phenols have a wide range of applications in various industries:

• In the production of plastics and resins, such as Bakelite.
• As intermediates in the synthesis of pharmaceuticals, including aspirin.
• In the manufacture of dyes and explosives.

Health and Safety

Phenols are known to be toxic and can cause severe burns upon contact with skin. They are also harmful if ingested or inhaled. Proper safety measures, including the use of personal protective equipment, are essential when handling phenols.

Environmental Impact

Phenols can be pollutants and are often found in industrial waste. They are subject to environmental regulations due to their toxicity and potential to cause harm to aquatic life.

See Also

• Aromatic compounds
• Hydroxyl group
• Alcohols
• Quinones
• Bakelite
• Aspirin