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Does Phenol Decolourise Bromine Water?

The question "does phenol decolourise bromine water" is a key consideration in understanding the chemical reactions between phenol and bromine. Phenol, a benzene ring with a hydroxyl group attached, exhibits unique reactivity due to the presence of the hydroxyl group. This article will delve into the interaction between phenol and bromine water, explaining why and how this reaction occurs, and its implications in chemical analysis.

The Chemistry Behind Phenol and Bromine Water

To answer the question, "does phenol decolourise bromine water," we need to first understand the chemical nature of phenol and bromine. Phenol is an aromatic compound, and its hydroxyl group significantly activates the benzene ring toward electrophilic substitution reactions. Bromine water, an aqueous solution of bromine, is typically orange-brown in color. When phenol is introduced into bromine water, a chemical reaction occurs, resulting in the decolourisation of the bromine water.

The Electrophilic Substitution Reaction

Phenol reacts with bromine water through an electrophilic substitution mechanism. The hydroxyl group in phenol is electron-donating and increases the electron density on the benzene ring, especially at the ortho and para positions relative to the hydroxyl group. When bromine water is added, bromine molecules are attracted to these positions, substituting hydrogen atoms in the ring and forming a white precipitate of 2,4,6-tribromophenol. As bromine is consumed in this reaction, the orange-brown color of the bromine water disappears, answering the question "does phenol decolourise bromine water" affirmatively.

Observation and Implications in Analysis

The decolourisation of bromine water in the presence of phenol is not only a confirmation of phenol's reactivity but also a useful qualitative test in organic chemistry. The ability of phenol to decolourise bromine water can be used as a diagnostic tool to distinguish phenol from other compounds that do not react with bromine in the same way. For example, alkenes also decolourise bromine water, but they do not produce the same white precipitate, making phenol's reaction unique.

Conclusion: Understanding the Reaction

In conclusion, the answer to "does phenol decolourise bromine water" is a clear yes. The reaction occurs due to the electrophilic substitution that takes place on the activated benzene ring of phenol, resulting in the formation of a white precipitate and the decolourisation of the bromine water. This reaction is a significant indicator of the presence of phenol and highlights the compound's unique chemical properties.