Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring

Problem 24a

Chapter 23, Problem 24a

Oxidation of a phenol derivative produces the lactone shown. Provide an arrow-pushing mechanism that rationalizes this outcome.

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Identify the phenol derivative structure and the lactone product. Recognize that the phenol derivative has an aromatic ring with a hydroxyl group attached, and the lactone is a cyclic ester.

Consider the oxidation process. Typically, phenol derivatives undergo oxidation to form quinones, which are key intermediates in forming lactones. The oxidizing agent will likely facilitate the conversion of the hydroxyl group to a carbonyl group.

Draw the initial step of the mechanism: the phenol derivative undergoes oxidation. Use arrow-pushing to show the movement of electrons from the hydroxyl group to form a carbonyl group, resulting in a quinone intermediate.

Next, illustrate the formation of the lactone. The quinone intermediate undergoes intramolecular nucleophilic attack, where an adjacent hydroxyl or alkoxy group attacks the carbonyl carbon, forming a cyclic structure. Use arrow-pushing to show this nucleophilic attack and the formation of the lactone ring.

Finally, ensure the mechanism accounts for any rearrangements or additional steps needed to stabilize the lactone product. This may involve proton transfers or tautomerization. Use arrow-pushing to show these final adjustments, resulting in the stable lactone structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phenol Oxidation

Phenol oxidation involves the conversion of phenolic compounds into more oxidized forms, often through the formation of quinones or other oxygen-containing functional groups. This process typically requires an oxidizing agent, such as chromic acid or hydrogen peroxide, which facilitates the removal of hydrogen atoms and the addition of oxygen.

Arrow-Pushing Mechanism

Arrow-pushing is a technique used in organic chemistry to illustrate the movement of electrons during chemical reactions. It involves drawing arrows to show how electron pairs move from nucleophiles to electrophiles, helping to visualize the step-by-step transformation of reactants into products. Understanding this concept is crucial for rationalizing reaction mechanisms.

Lactone Formation

Lactones are cyclic esters formed through the intramolecular esterification of hydroxy acids. In the context of phenol oxidation, lactone formation can occur when an oxidized phenol derivative undergoes a ring closure, typically involving the nucleophilic attack of an alcohol group on a carbonyl carbon, resulting in the release of water and the formation of the lactone ring.

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Related Practice

Textbook Question

Predict the product(s) of each of the following multistep reactions.

(a)

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Suggest reagents and reaction conditions that would result in synthesis of the following bromoalkanes.

(c)

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Textbook Question

Assessment 24.22 asked why meta-dihydroxybenzene could not be oxidized to meta-quinone. The attempted oxidation instead gives rise to three different quinone products. Suggest a mechanism for the formation of each.

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Textbook Question

(a) Based on Figure 24.23, explain why meta-dihydroxybenzene is not oxidized to meta-quinone.

(b) If a meta-quinone is not produced, what would you expect the product of the oxidation of meta-dihydroxybenzene to be?

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Textbook Question

In light of Figure 24.22, provide a mechanism by which para-dihydroxybenzene is oxidized to para-quinone.

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