Reactions of Aromatic Compounds

You may use these summaries and problems but you may NOT download them for use at another site, nor may you charge for access to them. Copyright Linda M. Sweeting 1997

The following example reactions are organized by type, with references to text chapters. Links within these summaries (which may show up as boxes around reagents) will provide further information about the reagents and their other reactions. Return to Graphical Reaction Summary menu for other functional group choices.

The first set of reactions are electrophilic substitutions for benzene only. At the end of this section, substituent effects on this reaction are summarized.

Halogenation


Br2 and FeBr3 will make bromobenzene, and Fe may be used instead of FeX3.
McMurry 16.1 Fessenden 11.8A, Schmid 21.5
Mechanism!

Nitration


McMurry 16.2, Fessenden 11.8C, Schmid 21.6
Mechanism!

Sulfonation


McMurry 16.2, Fessenden 11.8F, Schmid 21.7
Mechanism! Note that sulfonation is the only reversible aromatic substitution. Moreover, fusing arylsulfonic acids with sodium hydroxide (that means melted pure NaOH!) will convert the sulfonic acid to a phenol.

Alkylation - the Friedel-Crafts Reaction

+ +
McMurry 16.2, Fessenden 11.8D, Schmid 21.8
Mechanism!

Acylation - Friedel-Crafts

+
McMurry 16.3, Fessenden 11.8E, Schmid 21.9
Mechanism!
To reactions of ketones (reduction to CH2 is in Schmid 21.10)

If There Is Already a Substituent, You Need to Know the Effect of Substituents on Aromatic Substitution:

The Table Below is in Order of Decreasing Reactivity of Ring Containing the Substituent

Substituent Position of
Reaction		 log(rate
relative to H)
NR2 o, p 1.3
OH, OR o, p 0.9
R o, p 0.3
Ar o, p 0.2
F o, p 0.1
H "o, p" 0
NHCOR o, p -0.1
Cl, Br, I o, p -0.1
CO2H m -0.4
COR, CO2R m -0.5
CX3 m -0.5
SO3H m -0.6
CN m -0.7
NO2 m -0.8
NR3+ m -0.9

McMurry 16.3-16.9 Fessenden 11.9, Schmid 21.11
Mechanisms!
Some notes on multiple substitutions:
No alkylation or acylation is possible with substituents labelled "m" above (meta-directors), i.e. with rings less reactive than the halobenzenes.
Aniline is basic!!! In acids like H2SO4 or AlCl3 it becomes a meta-director. Use acetanilide, then hydrolyze.
Nucleophilic substitution of aromatic rings is possible, but especially if they are electron-deficient or a very strong base is used.

McMurry 16.8, Fessenden 12.4, Schmid 23.1-23.2

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