Question

Dimedone (Active methylene compound) an important reagent to characterise aldehyde, can be synthesised as shown below: $$ \mathrm{CH}_{3}-\mathrm{C}-\mathrm{CH}_{3} \stackrel{\mathrm{Ba}(\mathrm{OH})_{2}}{\Delta} \longrightarrow \frac{\mathrm{CH}_{2}\left(\mathrm{COOC}_{2} \mathrm{H}_{5}\right)_{2}}{\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{NNa}} \stackrel{\mathrm{H}_{3} \mathrm{O}^{+}}{\Delta} \text { Dimedone } $$ The structure of dimedone is (A) CC1(C)CCC(=O)CC1=O (B) CC1(C)C(=O)CCCC1=O (C) CC1(C)CC(=O)CC(=O)C1 (D) CC1(C)OC(=O)CC(=O)O1

Short answer

The correct structure of Dimedone is (C) \(CC1(C)CC(=O)CC(=O)C1\), as it contains a five-membered ring with two ketone groups and is consistent with the synthesis reaction steps.

Step-by-step solution

Analyze the reaction with Ba(OH)₂

In the first step of the reaction, the starting material CH₃-C-CH₃ reacts with Ba(OH)₂ under heat \(\Delta\) (delta symbol). This step involves the reaction between the starting material and Ba(OH)₂, where the barium ion is expected to replace one of the hydrogen atoms in the methylene group, forming a complex intermediate.

Analyze the reaction with H₃O⁺

In the second step, the intermediate complex reacts with H₃O⁺ under heat (\(\Delta\)) to synthesize Dimedone. In this step, the acidic medium (H₃O⁺) causes a protonation of one of the carbonyl groups, followed by a cyclization to form a five-membered ring containing the carbonyl group.

Identify the correct structure of Dimedone

With the reaction steps analyzed, let's examine each structure option and compare them with the expected structure formed during the synthesis steps. (A) \(CC1(C)CCC(=O)CC1=O \) - This structure contains a six-membered ring with two carbonyl groups (one ketone and one aldehyde), but it is not consistent with the expected cyclization of the synthesis reaction. (B) \(CC1(C)C(=O)CCCC1=O\) - This structure also contains a six-membered ring with two carbonyl groups (one ketone and one aldehyde), but like option (A), it doesn't match the expected cyclization. (C) \(CC1(C)CC(=O)CC(=O)C1\) - This structure has a five-membered ring with two ketone groups. It is consistent with the synthesis steps involving cyclization to form the five-membered ring with carbonyl groups. (D) \(CC1(C)OC(=O)CC(=O)O1\) - This structure also has a five-membered ring but contains an extra oxygen atom in the ring when compared to the other options. This structure is not consistent with the synthesis reaction provided. Based on the analysis of the synthesis steps and comparison with the provided structures, option (C) is the correct structure for Dimedone.

Key concepts

Active Methylene Compounds

Active methylene compounds are organic molecules characterized by the presence of acidic hydrogen atoms located between two carbonyl groups. These hydrogens are substantially more reactive because the adjacent carbonyl groups stabilize the resulting carbanion upon deprotonation.

This high reactivity is utilized extensively in various organic synthesis reactions.

Some properties of active methylene compounds include:

• Increased acidity compared to ordinary methylene groups
• A tendency to form strong hydrogen bonds
• The ability to engage in keto-enol tautomerism

In reactions such as the one involving dimedone synthesis, the active methylene compound allows for formation of an enolate, which is crucial for subsequent reaction steps. These enolates readily react with electrophiles, enabling the transformation of structures commonly seen in cyclization processes. Understanding active methylene compounds is essential for comprehending their role in synthesis and their reactivity in forming different chemical structures.

Dimedone Synthesis

Dimedone synthesis is a notable example of utilizing active methylene compounds. This process involves converting precursor compounds into a cyclic structure. The key steps in dimedone synthesis are the formation of intermediates through **nucleophilic** attacks and subsequent **cyclization** to achieve the final product.

The process begins with reacting a precursor containing an active methylene group in the presence of a base, such as Ba(OH)₂. This base facilitates the formation of an intermediate complex by attacking and deprotonating the methylene hydrogens. Once this intermediate is formed, it can bond further because of its enhanced reactivity.

In the final steps, the intermediate reacts with an acidic medium, like H₃O⁺, inducing a cyclization that completes the dimedone structure. The reaction conditions must be controlled carefully to obtain the correct product, ensuring that the correct chemical environment is maintained for promoting cyclization as opposed to unwanted side reactions.

Cyclization Reactions

Cyclization reactions are crucial in organic chemistry for creating cyclic compounds from linear precursors. These reactions involve the formation of a ring structure, often resulting in significant changes to the molecule's properties.

In the context of dimedone synthesis, cyclization occurs after forming a reactive intermediate from an active methylene group. The intermediate undergoes a transformation by closing into a ring, typically through a reaction with an electrophile such as H₃O⁺. The cyclization can result in either a five-membered or six-membered ring, although the five-membered furan ring is optimal in many synthesis pathways due to stability and reaction dynamics.

Cyclization reactions are influenced by things like:

• The type of ring that can form
• The presence of necessary functional groups
• Reaction conditions such as temperature and pH

These reactions are integral to forming a variety of chemical structures, making them a key element in organic synthesis, including pharmaceuticals and polymers.