Problem 37 - A Complete Resource Book in Chemistry for JEE Main

Question

Ziegler-Natta catalyst is (a) \(\mathrm{K}\left[\mathrm{PtCl}_{3}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\right]\) (b) \(\left(\mathrm{Ph}_{3} \mathrm{P}\right)_{3} \mathrm{RhCl}\) (c) \(\mathrm{Al}_{2}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{6}+\mathrm{TiCl}_{4}\) (d) \(\mathrm{Fe}\left(\mathrm{C}_{5} \mathrm{H}_{5}\right)_{2}\)

Step-by-Step Solution

Answer

The Ziegler-Natta catalyst is (c) \(\mathrm{Al}_{2}(\mathrm{C}_{2} \mathrm{H}_{5})_{6}+\mathrm{TiCl}_{4}\).

Step 1: Understand the Problem

The exercise is asking us to identify which one among the given options is a Ziegler-Natta catalyst. Ziegler-Natta catalysts are used in the polymerization of alkenes, particularly ethylene and propylene. They typically consist of titanium compounds paired with organoaluminum compounds.

Step 2: Evaluate Each Option

Review each chemical formula:(a) \mathrm{K[PtCl_{3}(C_{2}H_{4})]}: This involves a platinum complex, not typical of Ziegler-Natta catalysts.(b) \((\mathrm{Ph}_{3} \mathrm{P})_{3} \mathrm{RhCl}\): This is a rhodium-based complex, not associated with Ziegler-Natta catalysis.(c) \(\mathrm{Al}_{2}(\mathrm{C}_{2} \mathrm{H}_{5})_{6}+\mathrm{TiCl}_{4}\): This is an organoaluminum compound paired with a titanium tetrachloride compound, which is characteristic of Ziegler-Natta catalysts.(d) \(\mathrm{Fe}(\mathrm{C}_{5} \mathrm{H}_{5})_{2}\): This is an iron-based compound known as ferrocene, not used as a Ziegler-Natta catalyst.

Step 3: Identify the Correct Answer

Based on the evaluation, option (c) \(\mathrm{Al}_{2}(\mathrm{C}_{2} \mathrm{H}_{5})_{6}+\mathrm{TiCl}_{4}\) matches the description of a Ziegler-Natta catalyst as it consists of a combination typically used for polymerization processes.

Key Concepts

polymerization of alkenes

Polymerization is a chemical reaction where small molecules, called monomers, join together to form a larger molecule known as a polymer. Alkenes, which are hydrocarbons with carbon-carbon double bonds, are prime candidates for polymerization.

One of the most common reactions using Ziegler-Natta catalysts is the polymerization of alkenes like ethylene (C\(_2\)H\(_4\)) and propylene (C\(_3\)H\(_6\)).

This process transforms these gaseous alkenes into solid, durable plastics such as polyethylene and polypropylene, which are widely used in everyday products.

By using catalysts, the reaction becomes more efficient, allowing for the creation of polymers with specific properties. This is crucial in tailoring materials for specific applications.

Without such catalysts, the polymer chains would be shorter and less uniform, resulting in less desirable material properties.

organoaluminum compounds

Organoaluminum compounds are a key component of Ziegler-Natta catalysts. These compounds have applications not just limited to catalysis but also in other fields like organic synthesis.

In the context of Ziegler-Natta catalysis, organoaluminum compounds such as triethylaluminum (Al(C\(_2\)H\(_5\))\(_3\)) are used.

Here are some of their roles:

• They act as co-catalysts, playing a crucial role in activating the titanium component of the catalyst.
• This activation enables the catalysts to initiate the polymerization reaction efficiently.
• These compounds also assist by stabilizing the catalyst system, which helps achieve higher polymer yield.

Organoaluminum compounds are known for their reactivity with oxygen and water. Hence, they are usually handled under inert atmosphere conditions to prevent unwanted side reactions.

This sensitivity requires careful laboratory techniques but also contributes to their effectiveness in transforming alkene monomers into polymers.

titanium compounds

Titanium compounds form the backbone of the Ziegler-Natta catalyst, with titanium tetrachloride (TiCl\(_4\)) being one of the most commonly used.

These compounds are crucial because:

• They undergo activation by organoaluminum compounds, which allows them to facilitate the polymerization of alkenes.
• Titanium's unique properties help control the stereospecificity of the polymerization reaction.
• This control ensures the production of isotactic polymers, which have molecules aligned in a regular pattern, impacting the strength and durability of the material.

The unique role of titanium compounds in Ziegler-Natta catalysis has revolutionized the production of plastics, making them indispensable in the field of catalysis and materials science.

Despite their importance, titanium compounds must be handled carefully due to their reactivity, particularly in the presence of moisture and air.