Question

For the identification of \(\beta\) -naphthol using dye test, it is necessary to use (A) dichloromethane solution of \(\beta\) -naphthol. (B) acidic solution of \(\beta\) -naphthol. (C) neutral solution of \(\beta\) -naphthol. (D) alkaline solution of \(\beta\) -naphthol.

Short answer

(D) alkaline solution of \(\beta\)-naphthol.

Step-by-step solution

Understanding the Dye Test

The dye test for the identification of \(\beta\)-naphthol relies on the reaction of \(\beta\)-naphthol with a diazonium salt to form an azo dye. The chemical environment required for \(\beta\)-naphthol to undergo this reaction should promote the best interaction with the diazonium salt.

Recall the Chemistry of Azo Coupling Reactions

Azo coupling reactions involve the attack of an electron-rich aromatic compound like \(\beta\)-naphthol on a diazonium salt. The attacking species, in this case \(\beta\)-naphthol, should be deprotonated to act as a nucleophile. This is typically achieved under alkaline conditions.

Determine the Correct Option

Given that \(\beta\)-naphthol functions as a nucleophile in an azo coupling reaction, it requires an environment that will increase the nucleophilicity of the \(\beta\)-naphthol molecule. This is usually done by deprotonating the \(\beta\)-naphthol. Deprotonation occurs more readily in an alkaline solution, which provides hydroxide ions (OH-) that remove protons (H+) and increase nucleophilicity.

Key concepts

Dye Test Identification

The dye test is a method used in organic chemistry to identify compounds like \(\beta\)-naphthol through their ability to form bright colored azo dyes.

In this test, \(\beta\)-naphthol reacts with a diazonium salt; the resulting compound is an azo dye, recognizable by its distinct color. This process is known as an azo coupling reaction, and it is highly selective, meaning that only specific conditions will allow \(\beta\)-naphthol to react appropriately with the diazonium salt and form the dye.

For the identification of \(\beta\)-naphthol, the solution must promote a reaction by increasing the nucleophilic characteristics of the compound. These conditions are best met in an alkaline environment, where \(\beta\)-naphthol is deprotonated and can readily attack the diazonium salt, leading to the formation of the colorful azo dye. This shift in the environment is essential for the accurate identification of \(\beta\)-naphthol using the dye test.

β-Naphthol Properties

\(\beta\)-Naphthol is a white, crystalline compound that exhibits several unique properties making it ideal for various chemical reactions, including the formation of azo dyes.

This organic compound is slightly soluble in water, but more readily dissolves in alkaline solutions, which is essential for its reactivity. The chemical structure of \(\beta\)-naphthol includes a hydroxyl group (-OH) attached to the second position of a naphthalene ring; this structural feature is critical in azo coupling reactions.

In an alkaline solution, the hydroxide ions help deprotonate the hydroxyl group, effectively increasing the nucleophilicity of \(\beta\)-naphthol. This makes it more reactive and able to bond with diazonium salts to create azo dyes. Thus, understanding the physical and chemical properties of \(\beta\)-naphthol is key to manipulating its reaction pathways and identifying it through the dye test.

Alkaline Solution Reactions

Alkaline solutions play a crucial role in the realm of chemistry, particularly in reactions involving deprotonation of molecules such as \(\beta\)-naphthol.

An alkaline solution, characterized by a pH higher than 7, contains an excess of hydroxide ions (OH-). These ions are instrumental in increasing the nucleophilicity of certain compounds, which is a necessity in reactions like azo coupling.

In the context of the dye test for \(\beta\)-naphthol identification, the alkaline solution provides the ideal condition by deprotonating \(\beta\)-naphthol. This deprotonation allows the oxygen atom on the hydroxyl group to more effectively donate its pair of electrons to the diazonium salt, resulting in the formation of the azo bond that signifies a successful reaction.

It's also worth noting that alkaline solutions can affect the overall reaction rate and selectivity, making them an integral factor to consider in the synthesis of azo dyes and other similar reactions.