aromatic substitution l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Aromatic Substitution PowerPoint Presentation
Download Presentation
Aromatic Substitution

Loading in 2 Seconds...

play fullscreen
1 / 36

Aromatic Substitution - PowerPoint PPT Presentation


  • 287 Views
  • Uploaded on

Aromatic Substitution. Chapter 22. Reading Assignment. Sections 22.0 through 22.2 Sections 22.4 through 22.9 Sections 22.10 through 22.12 Section 22.17 Section 22.18 (chapter summary) Problems. Assigned Problems. In-text problems 22-1 through 22-2 22-4 through 22-13

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Aromatic Substitution' - Pat_Xavi


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
aromatic substitution

Aromatic Substitution

Chapter 22

WWU - Chemistry

reading assignment
Reading Assignment
  • Sections 22.0 through 22.2
  • Sections 22.4 through 22.9
  • Sections 22.10 through 22.12
  • Section 22.17
  • Section 22.18 (chapter summary)
  • Problems

WWU -- Chemistry

assigned problems
Assigned Problems
  • In-text problems
    • 22-1 through 22-2
    • 22-4 through 22-13
    • 22-23 through 22-29
  • End-of-chapter problems
    • 1 through 19

WWU -- Chemistry

substitution versus addition
Substitution versus Addition
  • Benzene does not undergo addition reactions.
  • To illustrate, consider the addition reaction of benzene and Br2:

WWU -- Chemistry

bromine addition to benzene
Bromine Addition to Benzene

As a result of the bromine addition, the benzene ring has lost its aromatic character -- it has lost its 150 kJ/mole of resonance energy. The reaction, as shown, is energetically unfavorable.

WWU -- Chemistry

bromine substitution on benzene
Bromine Substitution on Benzene
  • If, on the other hand, we allow a bromine atom to replace a hydrogen atom of benzene (i.e., a substitution reaction), the aromatic character of the benzene ring is retained.
  • This type of process remains energetically favorable.

WWU -- Chemistry

bromine substitution on benzene7
Bromine Substitution on Benzene

This is electrophilic aromatic substitution.

WWU -- Chemistry

electrophilic aromatic substitution
Electrophilic Aromatic Substitution
  • In general, the reactions of benzene follow the same pattern, as seen in the following image.
  • A+, in this reaction, is used to represent any electrophile (Lewis acid).

WWU -- Chemistry

common nomenclature in substituted benzenes14
Common Nomenclature in Substituted Benzenes
  • The ortho, meta, and para names can only be used when there are two substituents.
  • If there are three or more substituents, you must use the IUPAC name (with numbers).

WWU -- Chemistry

mechanism of electrophilic aromatic substitution
Mechanism of Electrophilic Aromatic Substitution
  • Nearly all the substitution reactions of benzene follow the same mechanism.
  • In the scheme that follows, A+ represents the electrophile (Lewis acid).

WWU -- Chemistry

slide20

All that is required is for us to figure out how to generate the appropriate A+ for any substitution reaction.

WWU -- Chemistry

reaction with acids
Reaction with Acids
  • Use H2SO4
  • What does this prove?
  • The hydrogens of benzene are exchangeable.
  • We can make “practical” use of this reaction in the following scenario:

WWU -- Chemistry

reaction with acids22
Reaction with Acids
  • Use D2SO4
  • Can use this method to prepare benzene-d6

WWU -- Chemistry

nitration of benzene
Nitration of Benzene
  • What does the H2SO4 do?
  • It reacts with nitric acid to generate the electrophile (see next image)

WWU -- Chemistry

formation of nitronium ion
Formation of Nitronium Ion

Nitronium ion (NO2+) is the electrophile that attacks the benzene ring.

WWU -- Chemistry

halogenation of benzene
Halogenation of Benzene
  • X can be either bromine or chlorine
  • Other catalysts might include elemental iron (Fe0) or aluminum chloride (AlCl3)
  • The ferric halide serves to generate the electrophile in this reaction.

WWU -- Chemistry

formation of the halonium ion
Formation of the Halonium Ion
  • X+ is a halonium ion:
    • Cl+ = chloronium ion
    • Br+ = bromonium ion
  • The halonium ion is the electrophile in this reaction.

WWU -- Chemistry

the friedel crafts alkylation reaction
The Friedel-Crafts Alkylation Reaction
  • The product is an alkylbenzene
  • The role of the anhydrous aluminum chloride is to generate a stable carbocation complex.
  • The carbocation is the electrophile in this process.

WWU -- Chemistry

explain this
Explain this:

WWU -- Chemistry

the friedel crafts acylation reaction
The Friedel-Crafts Acylation Reaction

The product is an acylbenzene (aromatic ketone)

WWU -- Chemistry

the friedel crafts acylation reaction31
The Friedel-Crafts Acylation Reaction
  • The role of the anhydrous aluminum chloride is to generate a stable carbocation complex.
  • The carbocation is the electrophile in this process.
  • In this case, the carbocation is an acylium ion.

WWU -- Chemistry

formation of a stable acylium ion complex
Formation of a Stable Acylium Ion Complex
  • The acylium ion is the electrophile in this reaction
  • Acylium ions do not rearrange
  • The same result is obtained if one uses an acid anhydride instead of an acid chloride.

WWU -- Chemistry

sulfonation of benzene
Sulfonation of Benzene
  • The actual electrophile in this reaction is sulfur trioxide.

WWU -- Chemistry

why is sulfur trioxide electrophilic
Why is Sulfur Trioxide Electrophilic?

sulfur

trioxide

The resulting ion reacts with benzene

WWU -- Chemistry

sulfonation of benzene36
Sulfonation of Benzene
  • The protonated SO3 is the electrophile in this reaction.
  • The reaction requires fuming sulfuric acid (i.e., sulfuric acid saturated with sulfur trioxide)
  • This reaction is reversible (unlike the other examples).

WWU -- Chemistry