Chapter 18- Reaction of Aromatics (Part II)

Question 1

What are the reactants used in a Friedel-Crafts Alkylation?

Answer 1

-An aromatic group
-A halide group
-AlX3

Question 2

How do you form the strong electrophile in Fieldel-Crafts Alkylation? (Hint: Draw it out)

Answer 2

Make a carbocation:

Question 3

Provide a mechanism and product for the following reaction (Act as if the electrophile has been made):

Answer 3

Question 4

In Frieldels-Craft Alkylation, what carbocation is favored? Secondary or Primary?

Answer 4

Secondary carbocations are favored because they are more stable.

Question 5

Name three possible issues with the Frieldels-Craft Alkylation.

Answer 5

Even though the carbon-carbon bonds are hard to form and Friedels-Craft Alkylation allows us to do that, there are reasons why it is not that efficient and therefore did not win a Nobel Prize (Massive L, clearly this was a bad craft.).

1) Polyalkination often is a result of this reaction, meaning the halide compound will add to multiple parts of the benzene ring.
2) Some substituted rings (for example: nitrobenzene) will not react because the molecule is too deactivated.
3) Halides can ONLY be attached to an sp3 group. This means halides attached to aromatic rings or alkenes will result in there being NO reaction.

Question 6

What is the Benzylic positon?

Answer 6

It is the position next to the benzene ring.

Question 7

What compound can we use to protonate an alkene to form a carbocation?

Answer 7

HF

Question 8

What can an alcohol be treated with to form a carbocation?

Answer 8

BF3

Question 9

True or False: Aromatic rings and alkyl groups are easily oxidized.

Answer 9

False

Question 10

True or False: Benzylic positons are easily oxidized.

Answer 10

True

Question 11

What two compounds are oxidizers for the benzylic positions? Which one is the better choice?

Answer 11

-Na2Cr2O7 (Chromic Acid)
-KMnO4 (Potassium Permaganate)

KMnO4 is the better choice because then you don’t have to deal with Chromium. Potassium Permaganate is more “green”.

Question 12

How many protons does the Benzylic positon need to undergo oxidation?

Answer 12

At least 1 proton is needed.

Question 13

Where does Free Radical Bromination occur?

Answer 13

At the benzylic position.

Question 14

Provide the two routes for Free Radical Bromination

Answer 14

-NBS (N-bromosuccinimide) and heat
-Br2 and hv (light)

Question 15

True or False: Benzylic bromides can NOT be used as synthetic intermediates.

Answer 15

False. They are great for elimination or substitution reactions.

Question 16

What reactants are used Friedel-Crafts Acylation?

Answer 16

-An acyl group
-AlX3

Question 17

How is the strong electrophile (Acylium ion) made? (Hint: Draw it Out)

Answer 17

Question 18

True or False: Polyacylation is NOT observed in Friedel-Crafts acylation.

Answer 18

True.

Question 19

How is benzaldehyde made?

Answer 19

-Gatterman-Koch Synthesis (what a name)

Question 20

What are the reactants in Gatterman-Koch?

Answer 20

-Benzene Ring
-CO
-HCl
-AlCl3 or alternatively CuCl

Question 21

What does Clemmensen reduction do?

Answer 21

Removes the C=O bond.

Question 22

What are the reactants in Clemmensen reduction?

Answer 22

-Zn(Hg)
-HCl, heat

Question 23

What is an alternative to Clemmensen reduction?

Answer 23

H2 and Pd/C (or Pt, if you have money).