Question

Which of the following will convert \(\mathrm{HC}=\mathrm{CCH}_{2} \mathrm{CH}_{3}\) to \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3} ?\) (1) \(\mathrm{H}_{2} \mathrm{O} / \mathrm{H}\) (2) \(\mathrm{Hg}^{21} / \mathrm{H}_{2} \mathrm{SO}_{4}\) (3) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (conc) \(/ \mathrm{H}_{3} \mathrm{PO}_{4}\) (4) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} / \mathrm{KMnO}_{4}\)

Short answer

Option 2 (\mathrm{Hg}^{21} / \mathrm{H}_{2} \mathrm{SO}_{4}\) will convert \mathrm{HC} = \mathrm{CCH}_{2}\mathrm{CH}_{3}\ to \mathrm{CH}_{3} \mathrm{COCH}_{2}\mathrm{CH}_{3}.\

Step-by-step solution

- Understanding the Target Product

First, identify the target product: \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\). This is a ketone with four carbon atoms.

- Analyze the Reactant

The given reactant is \(\mathrm{HC} = \mathrm{CCH}_{2} \mathrm{CH}_{3}\), which is propyne. Notice that it has an alkyne functional group.

- Determine the Appropriate Reagent

Identify the reagent that can convert an alkyne into a ketone. The conversion from an alkyne to a ketone typically involves hydration in the presence of mercuric sulfate (HgSO_4) and sulfuric acid (H_2SO_4).

- Match the Reagent

The reagent that matches this description from the options given is \(\mathrm{Hg}^{2+} / \mathrm{H}_{2} \mathrm{SO}_{4}\) (Option 2). This reagent will catalyze the addition of water across the triple bond of the alkyne, forming the ketone product.

- Verify the Correct Option

Verify that no other options fit the criteria better. Options 1, 3, and 4 do not provide the necessary conditions to convert an alkyne to a ketone.

- Conclusion

Conclude that the reagent \(\mathrm{Hg}^{2+} / \mathrm{H}_{2} \mathrm{SO}_{4}\) is the correct one to transform \(\mathrm{HC} = \mathrm{CCH}_{2} \mathrm{CH}_{3}\) to \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\).

Key concepts

organic chemistry

Organic chemistry is the study of carbon-containing compounds and their properties. It encompasses a wide array of substances, including all the materials found in living organisms as well as synthetic compounds like plastics. The foundation of organic chemistry lies in understanding how carbon atoms bond with other elements to form complex molecules.

One important class of compounds in organic chemistry is alkynes, which contain a carbon-carbon triple bond. Alkynes exhibit unique reactivity due to the triple bond, which can be manipulated to create various products. In this exercise, we are focusing on the transformation of a specific alkyne into a ketone.

Understanding how to manipulate alkyne structures is crucial in organic synthesis, which is used to construct complex molecules in pharmaceuticals, materials science, and more. Mastery of these transformations is a key aspect of advanced organic chemistry.

hydration of alkynes

Hydration refers to the addition of water (H₂O) to a molecule. In the context of alkynes, hydration involves adding water across the triple bond. This process typically requires a catalyst because alkynes are not reactive enough to hydrate on their own.

The hydration of alkynes generally follows Markovnikov's rule, which states that the hydrogen atom from the water molecule will attach to the carbon atom with more hydrogen atoms already attached, while the hydroxyl group (OH) will attach to the carbon atom with fewer hydrogen atoms. This ensures the formation of a more stable carbocation intermediate.

However, due to the triple bond structure, the hydration of alkynes often results in the formation of a ketone instead of an alcohol. This happens through a process where the initial enol (a molecule with a double bond and an alcohol group) tautomerizes to form a ketone, which is a more stable structure.

ketone synthesis

Ketone synthesis involves various chemical reactions that create ketones, which are organic compounds characterized by a carbonyl group (C=O) bonded to two carbon atoms. Ketones are significant in both biological processes and industrial applications.

In our specific problem, we are converting an alkyne into a ketone. The general approach involves hydration, where we add water across the alkyne's triple bond. This requires an acidic environment and a catalyst to proceed efficiently. The keto-enol tautomerization that follows is a natural process where the less stable enol form (an alcohol attached to a double-bond) rearranges into the ketone, which is thermodynamically favored.

Ketones have distinctive properties making them useful as solvents and intermediates for further chemical reactions. Understanding ketone synthesis is hence a foundational skill in organic chemistry, underpinning the development of many complex molecules.

mercuric sulfate catalysis

Mercuric sulfate (HgSO₄) catalysis plays a crucial role in the hydration of alkynes. The use of this catalyst facilitates the addition of water across the triple bond, a reaction that is otherwise slow and inefficient.

In the presence of sulfuric acid (H₂SO₄), mercuric sulfate helps form a reactive intermediate that enables the Markovnikov addition of water. This catalysis results in the production of an enol, which rapidly tautomerizes to form a ketone.

Mercuric sulfate catalysis is particularly useful because it allows for a controlled and selective hydration, preventing side reactions and ensuring the desired product formation. Without this catalyst, the reaction may not proceed efficiently or at all.

Understanding the role of this catalyst in organic reactions is essential for designing synthetic pathways and achieving the desired transformations in a laboratory setting.