Textbook Question
Show how each of the following compounds can be synthesized from benzene:
g. 2-phenylpropene
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19. Reactions of Aromatics: EAS and Beyond
EAS:Retrosynthesis
3:01 minutesProblem 65g
Textbook Question
Show how the following compounds can be synthesized from benzene:
g. p-dideuteriobenzene
Verified step by step guidance1
Step 1: Begin with benzene (C₆H₆) as the starting material. Benzene is a simple aromatic compound with a six-membered ring and alternating double bonds.
Step 2: To introduce deuterium (D) into the benzene ring, perform a deuterium exchange reaction. Treat benzene with deuterium gas (D₂) in the presence of a catalyst such as a platinum or palladium catalyst. This will replace all the hydrogen atoms in benzene with deuterium, forming perdeuterobenzene (C₆D₆).
Step 3: To selectively introduce deuterium at the para positions, first perform a Friedel-Crafts alkylation or acylation to introduce a directing group. For example, react benzene with an alkyl halide (e.g., CH₃Cl) or an acyl halide (e.g., CH₃COCl) in the presence of a Lewis acid catalyst (e.g., AlCl₃). This will introduce a substituent (e.g., CH₃ or COCH₃) at one position on the benzene ring.
Step 4: Use the substituent introduced in Step 3 as a directing group to guide the placement of deuterium. Treat the substituted benzene with D₂O (deuterium oxide) and a strong acid or base to exchange the hydrogen atoms at the ortho and para positions relative to the substituent with deuterium atoms. This will result in selective deuterium incorporation at the para position.
Step 5: Finally, remove the directing group introduced in Step 3 to regenerate the benzene ring with deuterium atoms at the para positions. For example, if a methyl group was used, perform a demethylation reaction. The final product will be p-dideuteriobenzene (C₆H₄D₂).
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Video duration:
3mKey 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, such as benzene. This process is crucial for synthesizing various derivatives of benzene, including substituted benzene compounds. Understanding EAS mechanisms, including the role of catalysts and the stability of intermediates, is essential for predicting the outcomes of reactions involving benzene.
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Deuteration
Deuteration is the process of replacing hydrogen atoms in a molecule with deuterium, a stable isotope of hydrogen. This is significant in organic synthesis, particularly when creating compounds like p-dideuteriobenzene, as it can alter the physical and chemical properties of the compound. Deuteration can be achieved through various methods, including the use of deuterated reagents in EAS reactions.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of synthesizing p-dideuteriobenzene from benzene, understanding regioselectivity is vital to ensure that deuterium is introduced at the correct positions on the aromatic ring. This concept is particularly important in EAS reactions, where the directing effects of substituents influence the outcome of the reaction.
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