Phenol Overview

  • Phenols are a type of aromatic hydrocarbon containing a hydroxyl (-OH) functional group attached to a carbon of a benzene ring.
  • They have a unique set of properties due to the resonance enhanced bonding between the -OH group and the benzene ring.

Acidity of Phenols

  • Phenols are somewhat acidic due to the polarity of the hydroxyl (OH) group.
  • They lose a hydrogen ion (H+) from the -OH group forming phenoxide ion, which is stabilised by resonance structures.
  • Therefore, phenols can neutralise bases and react with sodium, sodium hydroxide, and sodium bicarbonate to form salts.

Chemical Reactions of Phenols

  • Electrophilic Aromatic Substitution (EAS) Reactions: Phenols can undergo EAS reactions, for example bromination and nitration.
  • Esterification: Phenols react with carboxylic acids and acyl chloride to form esters.
  • Oxidation: Phenols can be oxidised to quinones, a class of compounds that play an important role in biological electron transfer processes.

Phenols in Medicine

  • Phenols have antiseptic properties and were widely used as disinfectants before the arrival of more modern substances.
  • The role of phenols as disinfectants has decreased, but their importance as a precursor in the preparation of medicines such as aspirin and paracetamol is key.
  • Other phenolic drugs include epinephrine (adrenaline), which is used to treat allergic reactions, and L-DOPA, which treats Parkinson’s disease.

Toxicity and Environmental Impact of Phenols

  • Phenols, especially in higher concentrations, can be hazardous and could cause burns or rashes.
  • They are toxic to the environment as well; excessive phenol levels can pose serious health hazards to aquatic ecosystems.
  • Understanding the properties and reactions of phenols is, therefore, important in environmental chemistry, and the development and use of medicinal products.