Textbook Question
Show how you would synthesize the following aromatic derivatives from benzene.
c. p-chlorotoluene
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19. Reactions of Aromatics: EAS and Beyond
EAS:Retrosynthesis
5:18 minutesProblem 49
Textbook Question
Starting from toluene, propose a synthesis of this trisubstituted benzene.
Verified step by step guidance1
Step 1: Begin with toluene (C6H5CH3) as the starting material. The methyl group on toluene is an activating group that directs electrophilic substitution reactions to the ortho and para positions.
Step 2: Perform a bromination reaction using Br2 and FeBr3 as a catalyst. This will introduce a bromine atom at the ortho position relative to the methyl group due to the activating effect of the methyl group.
Step 3: Oxidize the methyl group to a carboxylic acid group (-COOH) using a strong oxidizing agent such as KMnO4 or Na2Cr2O7 under acidic conditions. This converts toluene into benzoic acid with a bromine substituent at the ortho position.
Step 4: Introduce the amino group (-NH2) at the para position relative to the carboxylic acid group. This can be achieved by performing a nitration reaction using HNO3 and H2SO4 to add a nitro group (-NO2) at the para position, followed by reduction of the nitro group to an amino group using a reducing agent like Sn/HCl or Fe/HCl.
Step 5: If necessary, adjust the halogen substituent (e.g., convert Br to Cl) using a halogen exchange reaction such as Finkelstein reaction or other halogen substitution methods to achieve the desired final product structure.
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5mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Aromatic Substitution (EAS)
Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This reaction is crucial for synthesizing substituted aromatic compounds, such as the trisubstituted benzene in the question. Understanding the mechanism of EAS, including the role of activating and deactivating groups, is essential for predicting the outcomes of reactions starting from toluene.
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Directing Effects of Substituents
Substituents on an aromatic ring influence the position where new substituents will be added during electrophilic aromatic substitution. Activating groups, like -NH2, direct incoming electrophiles to the ortho and para positions, while deactivating groups, like -Cl, direct them to the meta position. Recognizing these directing effects is vital for planning the synthesis of the desired trisubstituted benzene from toluene.
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Functional Group Transformations
Functional group transformations involve converting one functional group into another through various chemical reactions. In the context of synthesizing the target compound, transformations such as nitration, reduction, and halogenation may be employed. Understanding these transformations allows chemists to strategically modify the starting material, toluene, into the desired product with specific functional groups like -COOH and -Cl.
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