a. Show how the following compounds can be prepared, using ethyne as one of the starting materials: 1. 1-pentyn-3-ol

Verified step by step guidance

1. Step 1: Start with ethyne (HC≡CH). The first step is to perform a nucleophilic addition of water to ethyne in the presence of a catalyst such as HgSO4 and H2SO4. This will result in the formation of acetaldehyde (CH3CHO).
2. Step 2: Next, perform a Grignard reaction. To do this, first convert the acetaldehyde into an alkyl halide by treating it with PBr3. This will result in the formation of 1-bromoethane (CH3CH2Br).
3. Step 3: Then, react the 1-bromoethane with magnesium in dry ether to form an ethyl Grignard reagent (CH3CH2MgBr).
4. Step 4: Now, perform a reaction between the ethyl Grignard reagent and propyne (CH3C≡CH) to form 1-pentyn-3-ol. The Grignard reagent will act as a nucleophile and attack the triple bond of propyne, resulting in the formation of the desired product.
5. Step 5: Finally, perform an acid workup by adding water to the reaction mixture. This will protonate the alkoxide intermediate, resulting in the formation of the final product, 1-pentyn-3-ol.

Key Concepts

Ethyne as a Building Block

Ethyne, also known as acetylene, is a simple alkyne that serves as a versatile building block in organic synthesis. Its triple bond allows for various reactions, including addition reactions with electrophiles, which can lead to the formation of more complex molecules. Understanding how to manipulate ethyne in synthetic pathways is crucial for preparing target compounds.

Alkyne Reactions

Alkynes undergo a variety of reactions, including hydration, hydroboration, and oxidation. In the case of preparing 1-pentyn-3-ol, the hydration of an alkyne can be achieved through acid-catalyzed reactions, leading to the formation of alcohols. Familiarity with these reactions and their mechanisms is essential for constructing the desired compound from ethyne.

Functional Group Transformation

Functional group transformations involve converting one functional group into another, which is a key strategy in organic synthesis. In this context, transforming an alkyne into an alcohol requires specific reagents and conditions. Understanding how to effectively perform these transformations is vital for synthesizing compounds like 1-pentyn-3-ol from ethyne.