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16 -- Part 10: AROMATIC COMPOUNDS
CH( CH ) 3 2 phenols are more reactive than CH( CH ) 3 2 phenols toward aromatic substitution.
sigma neutral complexes with structures that look like quinones are created when phenoxide ion react with positively charged electrophiles.
The phenoxide ion is so strongly activated that it undergoes an aromatic substitution with carbon dioxide.
The carboxylation of phenoxide ion is an industrial synthesis of salicylic acid, which is converted to aspirin.
A good Diels-Alder dienophile is 1,4-Benzoquinone.
Synthetic tools have been important for over a century.
Each new substitution affects where the next one will go.
The earlier substituents direct later reactions toward the correct reaction sites must be planned in any multistep sequence.
The product is determined by the order of substitution.
Attach the o,p-director first to produce the ortho or para product.
Attach the m-director first to produce the meta product.
Friedel-Crafts do not work well on strongly deactivated rings.
A strongly activated group wins when there is a conflict between substituents.
Friedel-Crafts reactions add acyl and alkyl groups to aromatic compounds, but they have limitations.
Straight-chain alkylbenzenes cannot be produced by simple Friedel-Crafts alkylation.
The Friedel-Crafts acylation can be used to convert the acyl group to an alkyl group.
If another group is to be added, it can be added to the acylbenzene to give meta orientation or it can be added to the alkylbenzene to give ortho,para orientation.
A student tried the Friedel-Crafts alkylation of benzenesulfonic acid with bromoethane.
An alternative synthesis can be proposed if not.
In alkylation, substitution can happen more than once.
A large excess of the starting aromatic compound is usually recycled through the process.
Friedel-Crafts reactions do not work on strongly deactivated benzenes.
The N: complexes with the AlCl3 catalyst become positively charged and become a deactivating group.
The amine can be protected from strongly acidic reagents by converting it to an amide.
The amide is compatible with Friedel-Crafts and many other reactions.
The amide can be removed at the end of the synthesis.
It works in Friedel-Crafts reactions.
Other reactions may be useful.
An aromatic ring can be attached to a carboxylic acid group by adding an alkyl group.
At the alkylbenzene stage, ortho and para can be added, or they can be added meta after the oxidation.
OH and NH2 substituents do not survive the oxidation.
SO3H and NO2 survive the oxidation.
This trisubstituted benzene starts from toluene.
A blocking group is the SO3H group.
The SO3H group can be used to block a position.
When the para position is more reactive, this is a common procedure to make ortho isomers.
The SO3H group can be used to block the para position, substitute the ortho position, and then remove the blocking group.
Sulfuration can be reversed.
If you start from toluene, you can propose synthetics for ortho-, meta-, and para-chlorobenzoic acid.
This trisubstituted benzene can be synthesised starting from toluene.
H2O reduction gives anilines.
There is a mixture of cis and trans.
The position of the benzylic is activated.
A catalyst is a protic acid or a Lewis acid.
There are no substitution of Aryl Halides for aryl halides in this section.
Special conditions are required for 2 carbon, usually involving a metal.
Chapter 17 has reactions shown in red.
Reactions are shown in blue.
A substituent makes the aromatic ring more reactive than benzene.
Acyl group bonds to a chlorine atom.
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