Textbook Question
Predict the products from the reactions of the following amines with sodium nitrite in dilute HCl.
(d) aniline
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19. Reactions of Aromatics: EAS and Beyond
Diazo Replacement Reactions
2:07 minutesProblem 25d,e
Textbook Question
Show how you would convert aniline to the following compounds.
(d) bromobenzene
(e) iodobenzene
Verified step by step guidance1
Step 1: Begin with aniline (C₆H₅NH₂) as the starting material. The amino group (-NH₂) on the benzene ring is highly activating and ortho/para-directing, so it must first be converted into a less reactive group to prevent unwanted side reactions during halogenation.
Step 2: Protect the amino group by converting it into an acetamide group. This can be achieved by reacting aniline with acetic anhydride (CH₃CO)₂O to form acetanilide (C₆H₅NHCOCH₃). The acetamide group is less activating and still ortho/para-directing.
Step 3: Perform the halogenation reaction. For bromobenzene, treat acetanilide with bromine (Br₂) in the presence of a mild Lewis acid catalyst such as FeBr₃. This will result in bromination at the para position relative to the acetamide group, forming para-bromoacetanilide.
Step 4: For iodobenzene, treat acetanilide with iodine (I₂) in the presence of an oxidizing agent such as nitric acid (HNO₃) or potassium iodate (KIO₃). This will result in iodination at the para position relative to the acetamide group, forming para-iodoacetanilide.
Step 5: Finally, hydrolyze the acetamide group back to the amino group by treating the halogenated acetanilide with aqueous acid or base (e.g., HCl or NaOH). This will yield the desired halogenated benzene derivatives: bromobenzene (C₆H₅Br) and iodobenzene (C₆H₅I).
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2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. Aniline, which contains an amino group (-NH2) that is a strong activating group, undergoes EAS readily. Understanding this mechanism is crucial for converting aniline to bromobenzene and iodobenzene, as it involves the introduction of halogens onto the aromatic ring.
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Halogenation of Aromatic Compounds
Halogenation is a specific type of electrophilic aromatic substitution where halogens (like bromine or iodine) are introduced to an aromatic compound. In the case of converting aniline to bromobenzene or iodobenzene, the reaction typically requires a halogen source (Br2 or I2) and a catalyst (like FeBr3 or I2) to facilitate the substitution. The choice of halogen and conditions affects the reaction's selectivity and yield.
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Deactivation of the Amino Group
While the amino group in aniline is a strong activating group for EAS, it can also lead to over-substitution or unwanted side reactions. To convert aniline to bromobenzene or iodobenzene, it may be necessary to temporarily deactivate the amino group, often by converting it to a less reactive form, such as an acetanilide. This step helps control the reaction conditions and ensures that only one halogen is introduced to the aromatic ring.
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