Phenols

Classification of Phenols Phenols classified according to the number of hydroxyl groups attached directly to the benzene ring 1- Monohydroxy phenol

Classification of Phenols 2- Dihydroxy phenol

Classification of Phenols 1- Trihydroxy phenol

Structure and Nomenclature of Phenols Phenols have hydroxyl groups bonded directly to a benzene ring Naphthols and phenanthrols have a hydroxyl group bonded to a polycyclic benzenoid ring

Nomenclature of Phenols Phenol is the parent name for the family of hydroxybenzenes Methylphenols are called cresols

Synthesis of Phenols Laboratory Synthesis Phenols can be made by hydrolysis of arenediazonium salts

Industrial Syntheses 1. Hydrolysis of Chlorobenzene (Dow Process) Chlorobenzene is heated with sodium hydroxide under high pressure The reaction probably proceeds through a benzyne intermediate 2. Alkali Fusion of Sodium Benzenesulfonate Sodium benzenesulfonate is melted with sodium hydroxide

Reactions of Phenols as Acids Strength of Phenols as Acids Phenols are much stronger acids than alcohols

Phenol is much more acidic than cyclohexanol Experimental results show that the oxygen of a phenol is more positive and this makes the attached hydrogen more acidic The oxygen of phenol is more positive because it is attached to an electronegative sp2 carbon of the benzene ring Resonance contributors to the phenol molecule also make the oxygen more positive

Distinguishing and Separating Phenols from Alcohols and Carboxylic Acids Phenols are soluble in aqueous sodium hydroxide because of their relatively high acidity Most alcohols are not soluble in aqueous sodium hydroxide A water-insoluble alcohol can be separated from a phenol by extracting the phenol into aqueous sodium hydroxide Phenols are not acidic enough to be soluble in aqueous sodium bicarbonate (NaHCO3) Carboxylic acids are soluble in aqueous sodium bicarbonate Carboxylic acids can be separated from phenols by extracting the carboxylic acid into aqueous sodium bicarbonate

Other Reactions of the O-H Group of Phenols Phenols can be acylated with acylation agents (acid chlorides and anhydrides )

Phenols in the Williamson Ether Synthesis Phenoxides (phenol anions) react with primary alkyl halides to form ethers by an SN2 mechanism

Cleavage of Alkyl Aryl Ethers Reaction of alkyl aryl ethers with HI or HBr leads to an alkyl halide and a phenol Recall that when a dialkyl ether is reacted, two alkyl halides are produced

Reaction of the Benzene Ring of Phenols Bromination The hydroxyl group is a powerful ortho, meta director and usually the tribromide is obtained Monobromination can be achieved in the presence of carbon disulfide at low temperature Nitration Nitration produces o- and p-nitrophenol Low yields occur because of competing oxidation of the ring

Sulfonation Sulfonation gives mainly the the ortho (kinetic) product at low temperature and the para (thermodynamic) product at high temperature

The Kolbe Reaction Carbon dioxide is the electrophile for an electrophilic aromatic substitution with phenoxide anion The phenoxide anion reacts as an enolate The initial keto intermediate undergoes tautomerization to the phenol product Kolbe reaction of sodium phenoxide results in salicyclic acid, a synthetic precursor to acetylsalicylic acid (aspirin)