Chapter 11 Phenols

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 Chapter 21

Nomenclature of Phenols Phenol is the parent name for the family of hydroxybenzenes Methylphenols are called cresols Chapter 21

Synthesis of Phenols Laboratory Synthesis Phenols can be made by hydrolysis of arenediazonium salts Chapter 21

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 (Section 21.11B) 2. Alkali Fusion of Sodium Benzenesulfonate Sodium benzenesulfonate is melted with sodium hydroxide Chapter 21

Reactions of Phenols as Acids Strength of Phenols as Acids Phenols are much stronger acids than alcohols Chapter 21

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 Chapter 21

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 Chapter 21

Other Reactions of the O-H Group of Phenols Phenols can be acylated with acid chlorides and anhydrides Chapter 21

Phenols in the Williamson Ether Synthesis Phenoxides (phenol anions) react with primary alkyl halides to form ethers by an SN2 mechanism Chapter 21

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 Chapter 21

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 Chapter 21

Sulfonation Sulfonation gives mainly the the ortho (kinetic) product at low temperature and the para (thermodynamic) product at high temperature Chapter 21

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) Chapter 21