Problem 16 - A Complete Resource Book in Chemistry for JEE Main

Question

Acetylene and HCHO react in the presence of copper acetylide catalyst to form (a) 2-butyne-1, 4 -diol (b) but-2-yne-1, 2 -diol (c) but-1-yne-1, 4 -diol (d) none of these

Step-by-Step Solution

Answer

(a) 2-butyne-1, 4-diol

Step 1: Understanding the Reaction

We are given that acetylene and formaldehyde (HCHO) react in the presence of a copper acetylide catalyst. This is a known reaction called the Reppe synthesis, where acetylene adds to aldehydes to form a diol.

Step 2: Identifying the Reactants

The reactants are acetylene ( ext{C}_2 ext{H}_2}) and formaldehyde ( ext{HCHO}). Acetylene will react twice with formaldehyde in this reaction to form a product, due to the presence of multiple reactive sites in acetylene (triple bond).

Step 3: Analyzing the Product

The reaction forms a diol. When acetylene reacts with two equivalents of formaldehyde, the expected product is 2-butyne-1,4-diol. This occurs due to the linear addition of the formaldehyde molecule on either side of acetylene's triple bond, leading to the formation of a four-carbon chain with hydroxyl groups on the terminal carbons.

Step 4: Verifying Against Given Options

Given the reaction product is 2-butyne-1, 4-diol, we compare with the provided options: (a) 2-butyne-1, 4-diol (b) but-2-yne-1, 2-diol (c) but-1-yne-1, 4-diol Clearly, option (a) matches exactly with what we have determined from the chemical reaction.

Key Concepts

Copper Acetylide Catalyst

The copper acetylide catalyst is a key component in reactions involving acetylene, such as the Reppe synthesis. A catalyst is something that speeds up a reaction without being consumed in the process. In this particular case, copper acetylide helps facilitate the reaction between acetylene and formaldehyde, ensuring that the desired product is formed efficiently and quickly.
Copper acetylide specifically assists in the activation of the acetylene molecule. It makes its triple bond more reactive, allowing for easier and more effective addition of the formaldehyde molecules.

• It is formed by the reaction of acetylene with copper(I) compounds.
• Highly effective in reactions involving unsaturated hydrocarbons.
• Ensures a cleaner reaction with fewer by-products.

Diol Formation

Diol formation is a process that results from the reaction between acetylene and formaldehyde, facilitated by the copper acetylide catalyst. A diol is an organic compound with two hydroxyl groups attached to separate carbon atoms.
The mechanism involves the addition of an aldehyde (formaldehyde, in this case) to each end of the acetylene molecule. This stepwise addition results in the formation of products like 2-butyne-1,4-diol, a four-carbon chain that holds hydroxyl groups on its terminal carbons.

• Diols are important in producing polymers and various chemical synthetics.
• They can serve as intermediates in the synthesis of more complex molecules.

By understanding the nature of diol formation in this reaction, we can predict products and harness the related techniques for industrial applications.

Acetylene and Formaldehyde Reaction

The reaction between acetylene and formaldehyde is a fascinating example of how simple organic molecules can come together to form more complex compounds, thanks to the catalytic role of copper acetylide. In our specific case, acetylene (\[\text{C}_2\text{H}_2\]) acts as the primary reactant along with formaldehyde (\[\text{HCHO}\]). The acetylene has a linear structure and a triple bond that provides two reactive pi-bonds.
In the presence of a copper acetylide catalyst, these pi-bonds in acetylene allow for reactions where molecules like formaldehyde add to these reactive sites. This process entails the formation of new carbon-oxygen bonds, which ultimately result in producing a product such as 2-butyne-1,4-diol.

• The acetylene-formaldehyde reaction is a perfect demonstration of synthetic chemistry.
• It applies principles of addition reactions where carbon and other atoms form new arrangements.
• Reppe synthesis assists in deriving chemical products with practical applications from smaller, more basic substances.