Question

Iodobenzene when heated with Cu powder gives (a) toluene (b) benzene (c) diphenyl (d) phenyl copper iodide

Short answer

Answer: Diphenyl

Step-by-step solution

Identify the Reactants

In this case, the reactants are iodobenzene and copper powder. Iodobenzene is an aromatic compound containing an iodine atom bonded to a benzene ring. Copper, in its powdered form, is a metal that can take part in chemical reactions.

Recall the Reaction Mechanism

This reaction is an example of the Ullmann reaction. In the Ullmann reaction, copper powder is used as a catalyst to facilitate the coupling and dehalogenation of aromatic halides.

Identify the Possible Products

We are given four possible products for the reaction: (a) Toluene (b) Benzene (c) Diphenyl (d) Phenyl copper iodide

Apply the Reaction Mechanism to the Reactants

According to the Ullmann reaction mechanism, the iodobenzene molecule undergoes coupling with another iodobenzene molecule in the presence of copper powder. This leads to the formation of the covalently bonded product, diphenyl, with the elimination of two molecules of iodide ion.

Determine the Correct Product

Based on the Ullmann reaction mechanism, the correct product formed in this reaction is diphenyl. So the correct option is: (c) Diphenyl Thus, when iodobenzene is heated with Cu powder, diphenyl is formed as the product.

Key concepts

Iodobenzene

Iodobenzene is a fascinating organic compound that plays a crucial role in chemical reactions. It consists of a benzene ring, which is a hexagonal ring of carbon atoms with alternating double bonds. The iodine atom is attached directly to one of the carbon atoms, making it an aromatic halide.

Iodobenzene is not just a simple aromatic molecule but a starting material in many reactions, particularly those involving coupling mechanisms. Its structure enables it to participate in various chemical transformations, such as the Ullmann reaction. In this reaction, it acts as a halide donor, facilitating the linking of aromatic rings.

Understanding Iodobenzene's structure and reactivity is essential when studying organic synthesis and transformations between different organic molecules.

Copper Powder

Copper powder is a finely divided form of copper metal. It is well-known for its enhanced surface area, which makes it particularly useful in chemical reactions.

In the context of the Ullmann reaction, copper powder is employed due to its catalyst-like properties. Although it is not consumed in the reaction, it facilitates the reaction between two molecules of iodobenzene.

This powdered form of copper supports the coupling of organic halides by providing a medium for electron transfer. Essentially, copper aids in breaking the carbon-halide bond and forming a new carbon-carbon bond. Such properties make copper powder an indispensable agent in several organic transformations.

Its role in reactions like the Ullmann reaction highlights its significance beyond common uses, showcasing its utility in complex organic chemical processes.

Aromatic Halides

Aromatic halides are compounds characterized by an aromatic ring bonded to a halogen atom, such as iodine in the case of iodobenzene. These compounds are pivotal in synthetic organic chemistry.

The presence of the halogen imparts unique properties to the aromatic ring, making it more reactive toward certain chemical transformations. In reactions like the Ullmann reaction, aromatic halides serve as precursors, allowing for the construction of more complex molecules.

They play a central role in various coupling reactions, where the halogen atom is replaced with another functional group or carbon moiety. This is achieved by breaking the carbon-halogen bond, often facilitated by catalysts like copper powder.

Understanding aromatic halides and their behavior is key to mastering organic synthesis, given their prevalence in pharmaceutical, agrochemical, and material science industries.

Coupling Reaction

Coupling reactions are a set of chemical reactions where two fragments, often containing carbon atoms, are joined together with the aid of a metal catalyst or reagent.

The Ullmann reaction is a classic example, where two molecules of an aromatic halide, such as iodobenzene, are linked to form a biaryl compound like diphenyl. This is accomplished in the presence of copper powder that facilitates the removal of halogen atoms and formation of new carbon-carbon bonds.

Key aspects of these reactions include:

• The use of a catalyst or reagent to drive the reaction.
• The formation of a new bond, often carbon-carbon, leading to larger and more intricate molecules.
• Their importance in synthesizing compounds in chemical industries.

Through coupling reactions, chemists can build complex organic structures efficiently. They are indispensable in developing pharmaceutical compounds, polymers, and other advanced materials.