Suggest the reagents used to effect the transformations shown.
(a)

Verified step by step guidance

1. Identify the starting material and the product. The starting material is a hydroquinone with an aldehyde group, and the product is a benzoquinone with a carboxylic acid group.
2. Recognize the transformation involved: the conversion of the aldehyde group to a carboxylic acid group, and the oxidation of the hydroquinone to benzoquinone.
3. Consider the reagents typically used for oxidizing hydroquinones to benzoquinones. Common oxidizing agents include potassium dichromate (K2Cr2O7) or silver oxide (Ag2O).
4. For the conversion of an aldehyde to a carboxylic acid, a mild oxidizing agent such as Tollens' reagent (Ag(NH3)2+) or Jones reagent (CrO3, H2SO4) can be used.
5. Combine the knowledge of both transformations to suggest a reagent or a sequence of reagents that can achieve both the oxidation of the hydroquinone and the aldehyde to carboxylic acid. A strong oxidizing agent like potassium permanganate (KMnO4) in acidic conditions can be effective for both transformations.

Key Concepts

Oxidation Reactions

Oxidation reactions involve the increase in oxidation state of a molecule, often by the addition of oxygen or the removal of hydrogen. In organic chemistry, oxidizing agents such as chromic acid or potassium permanganate are commonly used to convert alcohols or aldehydes to carboxylic acids or ketones. Understanding the role of oxidizing agents is crucial for predicting the outcome of such transformations.

Quinone Formation

Quinones are a class of cyclic organic compounds characterized by a fully conjugated cyclic dione structure. They are typically formed through the oxidation of phenols. In the given transformation, the conversion of a hydroquinone to a quinone involves the oxidation of the phenolic hydroxyl groups to carbonyl groups, which is a key step in the synthesis of quinones.

Reagent Selection for Oxidation

Selecting the appropriate reagent for oxidation is critical in organic synthesis. Common reagents include PCC, PDC, and Jones reagent, each with specific applications and selectivity. For the transformation of hydroquinone to benzoquinone, reagents like silver oxide or ferric chloride are often used due to their ability to selectively oxidize phenolic groups without over-oxidizing the molecule.