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.

Verified step by step guidance

1. Identify the starting material as meta-dihydroxybenzene, also known as resorcinol, which has hydroxyl groups at the 1 and 3 positions on the benzene ring.
2. Recognize that the oxidizing agent used is chromic acid (H2CrO4), which is a strong oxidizing agent capable of converting phenols to quinones.
3. Understand that the oxidation of resorcinol does not lead to a single meta-quinone product due to the instability of such a structure. Instead, the reaction proceeds through different pathways leading to multiple products.
4. Propose a mechanism for the formation of the first product: The hydroxyl group at the 1-position is oxidized to a carbonyl group, forming a para-quinone structure with the remaining hydroxyl group at the 3-position.
5. Suggest mechanisms for the formation of the other two products: The hydroxyl group at the 3-position is oxidized to a carbonyl group, forming an ortho-quinone structure with the remaining hydroxyl group at the 1-position. Additionally, a rearrangement or further oxidation could lead to the formation of a third quinone structure with different positioning of the carbonyl groups.

Key Concepts

Dihydroxybenzene Structure

Dihydroxybenzene, also known as catechol, has two hydroxyl (-OH) groups attached to a benzene ring. The position of these groups significantly affects the compound's reactivity. In meta-dihydroxybenzene, the hydroxyl groups are located at the 1,3-positions, which influences the electron distribution and steric hindrance during oxidation reactions.

Oxidation Mechanism

Oxidation in organic chemistry typically involves the loss of electrons or an increase in oxidation state. In the case of meta-dihydroxybenzene, the oxidation process can lead to the formation of quinones, which are cyclic compounds with a conjugated double bond system. Understanding the specific pathways and intermediates formed during oxidation is crucial for predicting the products.

Quinone Formation

Quinones are a class of cyclic organic compounds characterized by a six-membered ring with two carbonyl groups. The formation of different quinone products from meta-dihydroxybenzene can occur through various mechanisms, including rearrangements and the involvement of radical intermediates. Each pathway can yield distinct quinone structures based on the positions of the hydroxyl groups and the reaction conditions.