Question

On reaction of (phenyl benzoate) with \(\mathrm{Br}_{2}\), the major product obtained is

Short answer

The major product obtained when phenyl benzoate reacts with bromine (Br₂) is meta-brominated phenyl benzoate, with the structure \(PhOC(O)C_6H_4Br\).

Step-by-step solution

Identify the reactants

The given reaction is between phenyl benzoate and bromine (Br₂). The structure of phenyl benzoate is as follows: Phenyl benzoate: \(PhOC(O)C_6H_5\)

Identify the type of reaction

In this case, the reaction is an Electrophilic Aromatic Substitution (EAS). This type of reaction occurs when an electron-rich aromatic ring (like the benzene ring in phenyl benzoate) reacts with an electron-poor species (an electrophile, in this case, bromine).

Formation of the electrophile

Bromine (Br₂) can act as an electrophile when it reacts with aromatic rings. In this reaction, bromine forms a cyclic bromonium ion intermediate which acts as the electrophile.

Regioselectivity of the reaction

In EAS reactions, substituents on the aromatic ring can direct the incoming electrophile to specific positions on the ring. In this case, the ester group present in phenyl benzoate is a deactivating, meta-directing group. Thus, bromine will preferentially react at the meta position relative to the ester group. Since there are two phenyl rings in phenyl benzoate, bromination can occur on either ring at the meta position. However, the electron-withdrawing carbonyl group in the ester makes its attached benzene ring less reactive, so the major product would have the bromine added to the other phenyl ring.

Write the structure of the major product

The major product of the reaction is meta-brominated phenyl benzoate with the bromine added to the phenyl ring that is not directly attached to the ester group. The structure of the major product is as follows: Major product: \(PhOC(O)C_6H_4Br\) In conclusion, the major product obtained when phenyl benzoate reacts with bromine (Br₂) is meta-brominated phenyl benzoate.

Key concepts

Phenyl Benzoate

Phenyl benzoate is an organic compound where a benzene ring is attached to an ester functional group, specifically benzoic acid ester. This ester linkage is denoted by the chemical expression PhOC(O)C_6H_5, where Ph stands for the phenyl group. In phenyl benzoate, the ester group has a significant influence on the chemistry of the compound, especially when it undergoes reactions, such as Electrophilic Aromatic Substitution (EAS).

The ester group is considered an electron-withdrawing group (EWG), meaning it pulls electron density away from the benzene ring to which it's attached. This reduced electron density makes the benzene ring less reactive towards electrophilic attack. Understanding the electron-withdrawing nature of the ester group is crucial as it dictates the course of the reaction, including the regioselectivity, when phenyl benzoate is subjected to EAS processes like bromination.

Regioselectivity

Regioselectivity is a term used to describe the preference of a chemical reaction to form one directional isomer over others. In EAS, the position where new substituents are added to the aromatic ring depends on the existing substituents. These substituents are categorized as either ortho/para directors or meta directors based on their electronic effects.

The ester group in phenyl benzoate is a meta director because it is an electron-withdrawing group. During a reaction, this causes new substituents to favor the meta position rather than the ortho or para positions in relation to the ester group. This concept is fundamental in predicting the major product in EAS reactions, such as the bromination of phenyl benzoate, and is indispensable for students to grasp when analyzing reaction outcomes.

Reaction Mechanisms

A reaction mechanism explains the step-by-step process by which a chemical reaction occurs. In the case of phenyl benzoate reacting with bromine, the Electrophilic Aromatic Substitution mechanism involves several distinct steps:

• Formation of the electrophile - In the presence of a catalyst or under certain conditions, bromine can form a positively charged bromonium ion which is more electrophilic and ready to react with the benzene ring.
• Attack on the aromatic ring - The electrophile reacts with the electron-rich aromatic ring, leading to the formation of a sigma complex.
• Reestablishment of aromaticity - After the electrophile is added to the ring, a proton is lost, and the aromaticity of the benzene ring is restored.

Understanding this mechanism provides insight into how the structure of the major product is determined and why certain positions on the ring are more reactive than others.

Bromination of Aromatics

Bromination of aromatics is a specific type of Electrophilic Aromatic Substitution where bromine (Br_2) is introduced to an aromatic compound. The reaction is typically facilitated by the use of a catalyst such as iron (III) bromide (FeBr_3) or simply by exposure to light or heat which promotes the formation of the electrophilic bromine species.

In the case studied, where phenyl benzoate is the substrate, it’s critical to recognize that the reaction's regioselectivity is influenced by the ester group. The ester directs the bromination to the meta position of the more electron-rich phenyl ring. Through such EAS processes, complex organic compounds can be subtly modified to create a diverse array of products with varying properties and potential applications.