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When Phenol is Treated with Excess Bromine Water, It Gives: A Detailed Analysis

Phenol is an important aromatic compound with diverse applications in the chemical industry. When phenol is treated with excess bromine water, it gives a unique and specific reaction product that has significant implications in organic chemistry. This article will explore the chemical reaction, the mechanism behind it, and its practical significance. By understanding the details of this reaction, students and professionals alike can gain valuable insights into aromatic substitution reactions.

The Chemical Reaction of Phenol with Excess Bromine Water

When phenol is treated with excess bromine water, it gives 2,4,6-tribromophenol. This reaction is an example of electrophilic aromatic substitution, where bromine atoms are introduced into the aromatic ring of phenol. The reaction is highly specific due to the activating nature of the hydroxyl (-OH) group in phenol, which directs the bromination to the ortho and para positions relative to itself.

The overall chemical equation for the reaction is:

[ C6H5OH + 3Br2 (aq) \rightarrow C6H2Br3OH + 3HBr ]

This equation shows that three bromine molecules react with one phenol molecule to form 2,4,6-tribromophenol and hydrobromic acid as a byproduct.

The Mechanism Behind the Reaction

The hydroxyl group (-OH) in phenol is an electron-donating group, which makes the benzene ring highly activated towards electrophilic substitution. When phenol is treated with excess bromine water, it gives a reaction where the bromine acts as an electrophile. Here is a step-by-step breakdown of the reaction mechanism:

1. Activation of the Benzene Ring: The -OH group on phenol increases the electron density on the benzene ring, especially at the ortho and para positions. This makes these positions highly reactive towards electrophiles like bromine.

2. Formation of the Bromonium Ion: Bromine in water (Br2) dissociates to form Br+ (bromonium ion) and Br- ions. The Br+ ion is the active electrophile that will attack the benzene ring.

3. Substitution Reaction at Ortho and Para Positions: Due to the electron-donating effect of the -OH group, the Br+ ions preferentially attack the ortho and para positions. Since the reaction is conducted with excess bromine water, all three reactive positions (two ortho and one para) get substituted by bromine, forming 2,4,6-tribromophenol.

Practical Significance of the Reaction

Understanding what happens when phenol is treated with excess bromine water is important for several reasons:

1. Synthesis of Tribromophenol: 2,4,6-tribromophenol is a valuable compound in organic chemistry, often used as an intermediate in the synthesis of various pharmaceuticals, dyes, and agrochemicals. This reaction provides a simple and efficient method to produce tribromophenol in the laboratory or industrial settings.

2. Demonstration of Electrophilic Aromatic Substitution: This reaction is a classic example of electrophilic aromatic substitution, a fundamental concept in organic chemistry. It helps students understand how substituents on a benzene ring influence the reactivity and orientation of further substitutions.

3. Environmental and Safety Considerations: When phenol is treated with excess bromine water, it gives a product that requires careful handling. Both phenol and bromine are hazardous chemicals; hence, understanding this reaction is crucial for safe laboratory practices.

Conclusion

In conclusion, when phenol is treated with excess bromine water, it gives 2,4,6-tribromophenol, a compound that is widely used in various chemical applications. This reaction is not only a vital example of electrophilic aromatic substitution but also serves as an important synthesis route in the chemical industry. Understanding the detailed mechanism and implications of this reaction provides valuable insights into aromatic chemistry and helps build a solid foundation for further studies and applications.