Chapter 17- Reactions of Aromatic Compounds

Question 1

Why does the halogenation of aromatic rings require a catalyst?

Answer 1

Because alkenes are more reactive than benzene. The difference is resonance energy

Question 2

What is the catalyst in Bromination? In chlorination? In Iodination?

Answer 2

FeBr3 in Bromination

AlCl3 in Chlorination

Iodination requires an oxidation catalyst: HNO3, HIO3, SO3, H2O2

Question 3

What are the two methods for sulfonating aromatic rings?

Answer 3

1. SO3/ H2SO4- “fuming sulfuric acid” or “oleum.” Used to sulfonate benzene or aromatic rings deactivated by EWGs
2. H2SO4- Sulfuric Acid (96%). Used to sulfonate benzene rings activated by EDGs

Question 4

The sulfonation reaction in oleum is reversible or irreversible?

Answer 4

Irreversible.

Question 5

Sulfonation is (reversible or irreversible) in hot, dilute aqueous acid?

How is this reaction useful?

Answer 5

Reversible, it is useful b/c it can be used to install ortho/ para directing groups meta to one another, and then the sulfonic acid can be removed.

Question 6

What is the catalyst required in the F-C alkylation? What are the akylating reagents?

Answer 6

Catalyst- AlCl3 (aluminum trichloride)

Alkylating reagents- alkyl halides

Question 7

In the F-C alkylation, the catalyst complexes with the alkyl chloride to form what?

Answer 7

An incipient carbocation, which is not a true carbocation, but it acts like one.

Question 8

What are the limitations of the F-C alkylation?

Answer 8

1. Only works with alkyl halides (not vinyl or aryl halides)
2. Carbocation rearrangements occur (hydride and methyl shifts)
3. Strong EWGs on benzene ring inhibit reaction
4. Multiple substitutions possible

Question 9

What are the similarities and differences b/w F-C Alkylation and F-C Acylation?

Answer 9

Similarities:

1. AlCl3 is catalyst
2. Neither Acylation nor Alkylation of strongly deactivated rings not possible

Differences:

1. Intermediate electrophile does not rearrange in Acylation
2. Multiple substitutions not possible in Acylation
3. Acylation uses acyl halides and anhydrides and alkylation uses alkyl halides

Question 10

What are the two acylating agents in F-C Acylation?

Answer 10

1. Acid Anhydride

2. Acid Halide

Question 11

What is a very powerful tool in organic chemistry?

Answer 11

Synthesis of monosubstituted benzenes

Question 12

Inductive electron withdrawal/ donation occurs through what framework? What about resonance electron withdrawal/ donation?

Answer 12

Inductive- sigma bond framework

Resonance- pi system

Question 13

How do halides deactivate the ring? How do they direct ortho/ para?

Answer 13

Deactivation of ring- inductive withdrawal of electrons

Ortho/ para- directed via resonance donation

Question 14

Which kind of reaction is the nucleophilic aromatic substitution?

Answer 14

Addition- elimination

Question 15

Which substituents activate the ring for nucleophilic substitution?

Answer 15

Electron- withdrawing ortho and/ or para

Question 16

What kind of the reactant is the one for elmination- addition Benzyne rxn? What reagent do you use for this rxn?

Answer 16

A halobenzene with no ewgs on the ring.

Use a strong base like NaNH2 for reagent

Question 17

Why are Benzynes very reactive?

Answer 17

Because of the high strain on the triple bond

Question 18

What method adds alkyl groups to the benzene without the multiple limitations of the F-C reactions?

Answer 18

Aromatic substitutions using organometallic reagents

Question 19

How do you prepar lithium dialkylcuprate reagents (Gilman reagents)?

Answer 19

Reacting two eq of organolithium (2R- Li) with cuprious iodide (CuI).

2 R-Li + CuI —> R2CuI + LiI

Question 20

Why can’t coupling using organocuprate reagents react via Sn2?

Answer 20

B/c vinyl and aryl halides work well in this reaction

Question 21

What does the Heck Reaction entail? What does it produce? What is added to neutralize the HX produced?

Answer 21

Palladium- Catalyzed coupling of an aryl or vinyl halide with and alkene.

Produces C-C bond at the less subst end of alkene

Triethylamine or sodium acetate is added

Question 22

What does the Suzuki Coupling Reaction entail?

Answer 22

Palladium- catalyzed substitution that couples an aryl or vinyl halide with an alkyl, alkenyl, or aryl borinic acid or boronate ester

Question 23

What are the two ways to synthesize boronate esters?

Answer 23

1. Alkene + alkyl, vinyl, or arylboronic acids

2. Hydroborating alkyne or alkene

Question 24

What are required for catalytic hydrogenation? What are the possible catalysts?

Answer 24

Elevated heat and pressure required.

Possible catalysts: Pt, Pd, Ni, Ru, Rh

Reduction cannot be stopped at an intermediate stage

Question 25

What does the Side- Chain Oxidation reaction entail? What reagents are used? The benzylic carbon is oxidized to what?

Answer 25

Alkylbenzenes are oxidized to benzoic acid

Heat and KMNO4 or heat and Na2Cr2O7/ H2SO4 used

Benzylic carbon oxidized to carboxylic acid

Question 26

What are the 4 reactions of aromatic compounds?

Answer 26

1. Halogenation Y+ = Cl, Br
2. Friedel- Crafts Y+ = alkyl or acyl
3. Nitration Y+ = NO2
4. Sulfonation Y+ = SO3H