Chapter 12 :  Reactions of Arenes. Electrophilic Aromatic Substitution

Reactions and Reagents

The following table contains a summary of the key reactions to introduce a substituent onto an aromatic system.
More detailed information on each reaction can be accessed by following the link from the reaction column.
Reactions that can be used to convert existing aromatic substituents are listed separately.

Note that the reagent combination and reaction conditions for reactions of benzenes are usually more severe than reactions of alkenes.... this tends to make them more readily recognisable.

The following pointers may aid your understanding of these reactions:

• Recognise the electrophile present in the reagent combination
• The electrophile adds first to the arene
• Substitution is preferred over addition in order to preserve the stable aromatic character

Reaction	Reagents	Electrophile	Product	Comments
Nitration	HNO3 / H2SO4	NO2+		E+ formed by loss of water from nitric acid
Sulfonation	H2SO4 or SO3 / H2SO4	SO3		Reversible
Halogenation	Cl2 / Fe or FeCl3	Cl+		E+ formed by Lewis acid removing Cl-
	Br2 / Fe or FeBr3	Br+		E+ formed by Lewis acid removing Br-
Alkylation	R-Cl / AlCl3	R+		E+ formed by Lewis acid removing Cl-
	R-OH / H+	R+		E+ formed by loss of water from alcohol
	C=C / H+	R+		E+ formed by protonation of alkene
Acylation	RCOCl / AlCl3	RCO+		E+ formed by Lewis acid removing Cl-
	RCO2COR / AlCl3	RCO+		E+ formed by Lewis acid removing RCO2-