Question

Which of the following is the correct statement? (a) Acetylene is less reactive than ethylene in electrophilic addition reaction. (b) The hydrolysis of \(\mathrm{Mg}_{2} \mathrm{C}_{3}\) (Magnesium carbide) produces acetylene. (c) Ozonolysis of acetylene produces \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\). (d) Reduction of dialkyl acetylene using Lindlar's catalyst gives a trans olefin.

Short answer

(a) Acetylene is more reactive than ethylene in electrophilic addition reactions. (b) The hydrolysis of Mg2C3 (Magnesium carbide) produces acetylene. (c) The ozonolysis of acetylene produces carbon dioxide and water. (d) The reduction of dialkyl acetylene with Lindlar's catalyst produces a trans olefin. Answer: (b) The hydrolysis of Mg2C3 (Magnesium carbide) produces acetylene.

Step-by-step solution

Statement (a) analysis

We need to compare the reactivity of acetylene and ethylene in electrophilic addition reactions. Acetylene is an alkyne, while ethylene is an alkene. Alkynes are generally found to be less reactive than alkenes in electrophilic addition reactions due to the release of less energy when they are bonded. Therefore, statement (a) is correct.

Statement (b) analysis

The hydrolysis of magnesium carbide (\(\mathrm{Mg}_{2} \mathrm{C}_{3}\)) involves the reaction of magnesium carbide with water. The reaction is represented by the equation: \(\mathrm{Mg}_{2} \mathrm{C}_{3} + 4 \mathrm{H}_{2}\mathrm{O} \rightarrow 2 \mathrm{Mg}(\mathrm{OH})_{2} + 3 \mathrm{C}_{2}\mathrm{H}_{2}\). Here, we can see that acetylene (\(\mathrm{C}_{2}\mathrm{H}_{2}\)) is produced. Hence, statement (b) is correct.

Statement (c) analysis

Ozonolysis is the reaction of ozone (O3) with unsaturated compounds, like alkenes and alkynes. The reaction of acetylene with ozone produces carbon dioxide and water as products, and can be represented by the equation: \(\mathrm{C}_{2}\mathrm{H}_{2} + 6 \mathrm{O}_{3} \rightarrow 2 \mathrm{CO}_{2} + 2 \mathrm{H}_{2}\mathrm{O}\). So, statement (c) is also true.

Statement (d) analysis

Reduction of dialkyl acetylene using Lindlar's catalyst (palladium on calcium carbonate) involves selective hydrogenation. The reaction typically results in a cis olefin (also known as a Z-alkene), not a trans olefin (or E-alkene), which contradicts the given statement. Therefore, statement (d) is incorrect. Finally, after analyzing each statement, we can conclude that the correct statement among the given options is: (b) The hydrolysis of \(\mathrm{Mg}_{2} \mathrm{C}_{3}\) (Magnesium carbide) produces acetylene.

Key concepts

Electrophilic Addition

Electrophilic addition is a reaction where an electrophile forms a bond with the electrons found in a double or triple bond, usually of alkenes or alkynes. This kind of reaction is critical in organic chemistry because it helps convert unsaturated hydrocarbons into saturated ones. Ul>

Alkenes, like ethylene, have a double bond, which allows them to undergo electrophilic addition reactions easily.

Alkynes such as acetylene, contain a triple bond, making them less reactive than alkenes in these reactions.

The reason for this reduced reactivity lies in the stability of the molecule after the addition. When an electrophilic addition occurs, alkynes do not release as much energy as alkenes upon bond formation because the transition from triple to double bonds is less energetically favorable than double to single bonds. Thus, acetylene is less reactive towards electrophilic addition than ethylene, confirming our understanding of these reactions.

Hydrolysis of Carbides

In the world of organic chemistry, the term hydrolysis represents the chemical breakdown of a compound due to the addition of water. When it comes to carbides, hydrolysis can deliver fascinating results.Magnesium carbide (\(\mathrm{Mg}_{2}\mathrm{C}_{3}\)) is a clear example. When this compound undergoes hydrolysis, it reacts with water to produce acetylene (\(\mathrm{C}_{2}\mathrm{H}_{2} \) ), which is a key starting material in organic synthesis. Let’s examine this neatly:

• Magnesium carbide reacts with water.
• Products include magnesium hydroxide (\(\mathrm{Mg(OH)}_{2}\) ) and acetylene (\(\mathrm{C}_{2}\mathrm{H}_{2}\) ).

The formation of acetylene is crucial because of its applications in industrial operations, particularly in the production of plastics and the synthesis of other important organic compounds.

Ozonolysis

Ozonolysis is a reaction involving ozone (\(\mathrm{O}_{3}\)), used to cleave double or triple bonds in organic compounds, producing smaller fragments. This reaction is especially useful in revealing the structure of complex organic molecules by breaking them into simpler, recognizable components.Specifically, when acetylene undergoes ozonolysis, the molecules split, leading to products like carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). This is captured in the equation:\(\mathrm{C}_{2}\mathrm{H}_{2} + 6 \mathrm{O}_{3} \rightarrow 2 \mathrm{CO}_{2} + 2 \mathrm{H}_{2}\mathrm{O} \)This process allows chemists to determine the positions of double or triple bonds within an unsaturated organic molecule, making it a valuable analytical tool in organic chemistry.

Lindlar's Catalyst

Lindlar's catalyst provides a unique approach in the delicate arena of hydrogenation reactions. Composed of palladium deposited on calcium carbonate and usually poisoned with lead or quinoline, Lindlar's catalyst performs selective hydrogenation of triple bonds to double bonds without progressing to single bonds. This selectivity is key for generating cis alkenes from alkynes.

• So in a typical reaction, Lindlar's catalyst reduces a dialkyl acetylene to a cis alkene (or Z-alkene).
• This stops the reaction at the double bond stage, effectively preventing the full reduction to a single bond.

Contrary to the mistake often made, it produces a cis, not a trans alkene, demonstrating the precision required in these reactions. This ability to selectively form certain products makes Lindlar's catalyst important in producing fine chemicals and pharmaceuticals efficiently.