Chapter 11 Phenols t Structure and Nomenclature of

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Chapter 11 Phenols

Chapter 11 Phenols

t Structure and Nomenclature of Phenols èPhenols have hydroxyl groups bonded directly to a

t Structure and Nomenclature of Phenols èPhenols have hydroxyl groups bonded directly to a benzene ring H Naphthols and phenanthrols have a hydroxyl group bonded to a polycyclic benzenoid ring Chapter 21 2

l Nomenclature of Phenols èPhenol is the parent name for the family of hydroxybenzenes

l Nomenclature of Phenols èPhenol is the parent name for the family of hydroxybenzenes H Methylphenols are called cresols Chapter 21 3

t Synthesis of Phenols l Laboratory Synthesis èPhenols can be made by hydrolysis of

t Synthesis of Phenols l Laboratory Synthesis èPhenols can be made by hydrolysis of arenediazonium salts Chapter 21 4

l Industrial Syntheses è 1. Hydrolysis of Chlorobenzene (Dow Process) Chlorobenzene is heated with

l Industrial Syntheses è 1. Hydrolysis of Chlorobenzene (Dow Process) Chlorobenzene is heated with sodium hydroxide under high pressure H The reaction probably proceeds through a benzyne intermediate (Section 21. 11 B) H è 2. Alkali Fusion of Sodium Benzenesulfonate H Sodium benzenesulfonate is melted with sodium hydroxide Chapter 21 5

t Reactions of Phenols as Acids l Strength of Phenols as Acids èPhenols are

t Reactions of Phenols as Acids l Strength of Phenols as Acids èPhenols are much stronger acids than alcohols Chapter 21 6

èPhenol is much more acidic than cyclohexanol èExperimental results show that the oxygen of

èPhenol is much more acidic than cyclohexanol èExperimental 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 sp 2 carbon of the benzene ring H Resonance contributors to the phenol molecule also make the oxygen more positive H Chapter 21 7

l Distinguishing and Separating Phenols from Alcohols and Carboxylic Acids èPhenols are soluble in

l Distinguishing and Separating Phenols from Alcohols and Carboxylic Acids èPhenols are soluble in aqueous sodium hydroxide because of their relatively high acidity Most alcohols are not soluble in aqueous sodium hydroxide H A water-insoluble alcohol can be separated from a phenol by extracting the phenol into aqueous sodium hydroxide H èPhenols are not acidic enough to be soluble in aqueous sodium bicarbonate (Na. HCO 3) Carboxylic acids are soluble in aqueous sodium bicarbonate H Carboxylic acids can be separated from phenols by extracting the carboxylic acid into aqueous sodium bicarbonate H Chapter 21 8

t Other Reactions of the O-H Group of Phenols èPhenols can be acylated with

t Other Reactions of the O-H Group of Phenols èPhenols can be acylated with acid chlorides and anhydrides Chapter 21 9

l Phenols in the Williamson Ether Synthesis èPhenoxides (phenol anions) react with primary alkyl

l Phenols in the Williamson Ether Synthesis èPhenoxides (phenol anions) react with primary alkyl halides to form ethers by an SN 2 mechanism Chapter 21 10

t Cleavage of Alkyl Aryl Ethers èReaction of alkyl aryl ethers with HI or

t Cleavage of Alkyl Aryl Ethers èReaction of alkyl aryl ethers with HI or HBr leads to an alkyl halide and a phenol H Recall that when a dialkyl ether is reacted, two alkyl halides are produced Chapter 21 11

t Reaction of the Benzene Ring of Phenols l Bromination èThe hydroxyl group is

t Reaction of the Benzene Ring of Phenols l Bromination èThe hydroxyl group is a powerful ortho, meta director and usually the tribromide is obtained H Monobromination can be achieved in the presence of carbon disulfide at low temperature l Nitration èNitration produces o- and p-nitrophenol H Low yields occur because of competing oxidation of the ring Chapter 21 12

l Sulfonation èSulfonation gives mainly the ortho (kinetic) product at low temperature and the

l Sulfonation èSulfonation gives mainly the ortho (kinetic) product at low temperature and the para (thermodynamic) product at high temperature Chapter 21 13

l The Kolbe Reaction è Carbon dioxide is the electrophile for an electrophilic aromatic

l The Kolbe Reaction è Carbon dioxide is the electrophile for an electrophilic aromatic substitution with phenoxide anion The phenoxide anion reacts as an enolate H The initial keto intermediate undergoes tautomerization to the phenol product H Kolbe reaction of sodium phenoxide results in salicyclic acid, a synthetic precursor to acetylsalicylic acid (aspirin) H Chapter 21 14