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How Will You Convert Aniline into Benzoic Acid?

The conversion of aniline into benzoic acid is a multi-step chemical process that involves transforming an amine group into a carboxylic acid group. This transformation is essential in organic synthesis and has several applications in chemical industries. In this article, we will explore the steps involved in converting aniline into benzoic acid and discuss the underlying principles that make this conversion possible.

Step 1: Nitration of Aniline

The first step in converting aniline into benzoic acid involves the nitration of aniline to form nitrobenzene. Aniline is highly reactive towards electrophilic substitution reactions due to the presence of the electron-donating amino group (-NH2). However, direct nitration of aniline leads to multiple substitutions on the benzene ring, which is undesirable. Therefore, to prevent over-nitration, aniline is first acetylated to form acetanilide. The acetyl group acts as a protective group, reducing the electron density on the ring and allowing for controlled nitration.

The acetylation of aniline can be achieved by reacting aniline with acetic anhydride, producing acetanilide. The acetanilide is then subjected to nitration using a mixture of concentrated nitric acid and sulfuric acid, leading to the formation of p-nitroacetanilide.

Step 2: Hydrolysis of Nitroacetanilide

After nitration, the nitroacetanilide undergoes hydrolysis to remove the acetyl protecting group, yielding p-nitroaniline. The hydrolysis can be performed by heating the nitroacetanilide in an aqueous acidic or basic solution. This step is crucial because it regenerates the amino group while retaining the nitro group on the benzene ring.

The hydrolysis reaction can be summarized as follows:

[ \text{C8H8N2O3 (p-nitroacetanilide)} + \text{H2O} \rightarrow \text{C6H6N2O2 (p-nitroaniline)} + \text{CH3COOH} ]

Step 3: Oxidation of p-Nitroaniline

The next critical step in converting aniline into benzoic acid is the oxidation of p-nitroaniline. The nitro group in p-nitroaniline is a strong electron-withdrawing group, making the amino group susceptible to oxidation. Oxidizing agents such as potassium permanganate (KMnO4) or chromium trioxide (CrO3) in acidic medium can be used for this oxidation process. The oxidation of p-nitroaniline results in the formation of p-nitrobenzoic acid.

The oxidation reaction can be represented as follows:

[ \text{C6H6N2O2 (p-nitroaniline)} + [O] \rightarrow \text{C7H5NO_4 (p-nitrobenzoic acid)} ]

Step 4: Reduction of p-Nitrobenzoic Acid

The final step involves reducing the nitro group in p-nitrobenzoic acid to form benzoic acid. This reduction can be carried out using catalytic hydrogenation or by employing reducing agents like tin (Sn) in hydrochloric acid (HCl). The nitro group is reduced to an amino group, followed by a spontaneous deamination to form benzoic acid.

The reduction reaction can be expressed as:

[ \text{C7H5NO4 (p-nitrobenzoic acid)} + 6[H] \rightarrow \text{C7H6O2 (benzoic acid)} + NH3 + H2O ]

Conclusion

In summary, the process of converting aniline into benzoic acid involves a series of carefully controlled reactions, including nitration, hydrolysis, oxidation, and reduction. Each step is crucial for ensuring the successful transformation of the amino group in aniline into a carboxylic acid group, resulting in the formation of benzoic acid. Understanding this sequence of reactions provides valuable insight into organic synthesis and the broader field of chemical engineering. For those searching for the most effective method to answer the question "how will you convert aniline into benzoic acid," the above steps offer a comprehensive guide to achieve this transformation.