Phenolat

Phenolat, more commonly called phenolate or phenoxide, is the conjugate base of phenol. It is the negatively charged oxygen-centered anion formed when phenol loses a proton, and it typically exists as a salt with a counterion such as sodium, potassium, or lithium (for example, sodium phenoxide). The negative charge is delocalized by resonance not only on the oxygen but also into the ortho and para positions of the aromatic ring, giving a relatively stable, resonance-stabilized anion.

Preparation and properties

Phenol is moderately acidic for an organic compound, with a pKa around 9–11 depending on substituents. It can be deprotonated by strong bases such as sodium hydroxide or sodium hydride to give phenolate salts. These salts are typically more soluble and reactive in various organic solvents than phenol itself. Phenolates are basic and can be caustic; they require careful handling.

Reactions and uses

Phenolates are versatile nucleophiles in organic synthesis. In Williamson ether synthesis, they react with alkyl halides or sulfonates to form aryl or alkyl aryl ethers. The high electron density of the phenoxide ion also directs electrophilic substitution on the ring to the ortho and para positions in many substituted phenols. Beyond lab-scale chemistry, phenolates are used as intermediates in the production of polymers, dyes, and various specialty chemicals.

Occurrence and terminology

Phenolates do not typically occur as stable free species in nature, but arise as reactive intermediates or salts in industrial processes and biological contexts. The term phenolate/phenoxide is used interchangeably in many contexts, with “phenolate ion” emphasizing the anionic form.