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Ch. 18 - Ketones and Aldehydes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 18 - Ketones and AldehydesProblem 60c
Chapter 18, Problem 60c

Show how you would accomplish the following syntheses.
(c) benzene → p-methoxybenzaldehyde

Verified step by step guidance
1
Step 1: Begin with benzene as the starting material. Perform a Friedel-Crafts acylation reaction using paraformaldehyde (CH2O) and an acid catalyst such as AlCl3 to introduce a formyl group (-CHO) at the para position relative to the benzene ring.
Step 2: Protect the aldehyde group by converting it into an acetal. React the aldehyde with methanol (CH3OH) in the presence of an acid catalyst (e.g., HCl) to form the dimethyl acetal derivative.
Step 3: Introduce the methoxy group (-OCH3) at the para position. Perform an electrophilic aromatic substitution reaction using methanol and a Lewis acid catalyst (e.g., AlCl3) to replace the hydrogen atom at the para position with the methoxy group.
Step 4: Deprotect the acetal group to regenerate the aldehyde. Use an acidic hydrolysis reaction (e.g., HCl in water) to convert the acetal back into the aldehyde group.
Step 5: Verify the structure of the final product, p-methoxybenzaldehyde, ensuring the methoxy group is at the para position relative to the aldehyde group on the benzene ring.

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Key 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 process is crucial for modifying aromatic compounds, such as benzene, to introduce various functional groups. Understanding the mechanism of EAS, including the role of the electrophile and the stability of the carbocation intermediate, is essential for synthesizing compounds like p-methoxybenzaldehyde.
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Ortho/Para Directing Groups

In EAS reactions, substituents on the aromatic ring can influence the position where new groups are added. Electron-donating groups, such as methoxy (-OCH3), are ortho/para directing, meaning they favor substitution at the ortho or para positions relative to themselves. Recognizing how these directing effects operate is vital for predicting the outcome of the synthesis from benzene to p-methoxybenzaldehyde.
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Formylation of Aromatic Compounds

Formylation is the introduction of a formyl group (-CHO) into an aromatic compound, typically achieved through the Vilsmeier-Haack reaction or the Gattermann-Koch reaction. This step is essential in the synthesis of p-methoxybenzaldehyde, as it allows for the conversion of the methoxy-substituted aromatic compound into the desired aldehyde. Understanding the conditions and reagents required for effective formylation is crucial for successful synthesis.
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Related Practice
Textbook Question

There are three dioxane isomers: 1,2-dioxane, 1,3-dioxane, and 1,4-dioxane. One of these acts like an ether and is an excellent solvent for Grignard reactions. Another one is potentially explosive when heated. The third one quickly hydrolyzes in dilute acid. Show which isomer acts like a simple ether, and then explain why one of them is potentially explosive.

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Textbook Question

There are three dioxane isomers: 1,2-dioxane, 1,3-dioxane, and 1,4-dioxane. One of these acts like an ether and is an excellent solvent for Grignard reactions. Another one is potentially explosive when heated. The third one quickly hydrolyzes in dilute acid. Propose a mechanism for the acid hydrolysis of the third isomer.

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Textbook Question

Show how you would accomplish the following syntheses.

(a) benzene → n-butylbenzene

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Textbook Question

Show how you would accomplish the following syntheses.

(b) benzonitrile → propiophenone

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Textbook Question

The Wittig reaction is useful for placing double bonds in less stable positions. For example, the following transformation is easily accomplished using a Wittig reaction.

(a) Show how you would use a Wittig reaction to do this.

(b) Show how you might do this without using a Wittig reaction, and then explain why the Wittig reaction is a much better synthesis.

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Textbook Question

Show how you would accomplish the following syntheses.

(d)

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