Electrophilic Aromatic Substitution

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Electrophilic Aromatic Substitution
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EAS Mechanism
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Bromination Requires a Catalyst
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Deprotonation gives Aromatic Structure
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Phenyl-H 112 kcal mol-1 Br-Br 46 kcal
mol-1 Phenyl-Br -81 kcal mol-1 H-Br -87.5
kcal mol-1 ---------------------------------------
------------------ Reaction -10.5
kcal mol-1
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Nitration and Sulfonation
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Nitric Acid activated by Sulfuric Acid
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Electrophilic Addition of Nitro Group
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Nitration and Sulfonation
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Sulfonation is Reversible
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Sulfonate Applications
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Sulfonate Applications
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Sulfa Drugs
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Friedel-Crafts Alkylation
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Friedel-Crafts Mechanism
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Intramolecular Friedel-Crafts
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Other Carbocation Precursors Can Be Used
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Friedel-Crafts Alkylation has Limitations
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Rearrangement Can Also Occur
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End Lecture 17
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Friedel-Crafts Acylation
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Reaction Gives Ketone as Product
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Acylium Ion Formation
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Electrophilic Acylation
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Aqueous workup is required
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Ketone Reduction
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Summary

• Electrophilic Aromatic Substitution
• The most important reaction of benzene
• Rate determining step is addition by the
  electrophile
• Exothermic substitution preferred over
  endothermic addition
• Leads to halo- and nitrobenzenes, benzenesulfonic
  acids, alkylated and alkanoylated derivatives

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Summary
Sulfonation of benzene is reversible by heating
with dilute aqueous acid Benzenesulfonic Acids
Precursors of benzenesulfonyl chlorides. These
chlorides React with alcohols to form sulfonic
esters containing useful leaving groups React
with amines to give sulfonamides (some of which
are medically important) Friedel-Crafts
Alkylations Activate the aromatic ring to
further electrophilic substitution which leads to
product mixtures
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