What Is Nitroaniline?
Nitroaniline is an organic compound belonging to the aromatic amine family, in which one hydrogen atom on the aromatic ring of aniline is replaced by a nitro group.
The chemical formula is C6H6N2O2, with a molecular weight of 138.126. There are three isomers, depending on the position of the nitro group: 2-Nitroaniline (o-Nitroaniline), 4-Nitroaniline (p-Nitroaniline), and 3-Nitroaniline (m-Nitroaniline).
Generally, 4-nitroaniline is the most widely used, with CAS registration numbers 88-74-4 (2-nitroaniline), 99-09-2 (3-nitroaniline), and 100-01-6 (4-nitroaniline).
Uses of Nitroaniline
Nitroaniline is primarily used as an intermediate in the synthesis of dyes, pharmaceuticals, antioxidants, gasoline gum inhibitors, poultry medications, and corrosion inhibitors. 4-nitroaniline serves as a raw material for the synthesis of the red azo dye, Para Red.
Para Red, developed in 1880, was the world’s first azo dye and remains significant for its easy coloring, deep coloration, and excellent light and heat resistance.
3-Nitroaniline is used as a synthetic intermediate, especially for azo dyes, from which yellow and blue dyes are synthesized.
Properties of Nitroaniline
1. Basic Information on 2-Nitroaniline
2-nitroaniline, an orange crystal at room temperature, has a melting point of 71-72°C and a boiling point of 284°C. It is slightly soluble in ethanol and diethyl ether, and very insoluble in water.
2. Basic Information on 3-Nitroaniline
3-nitroaniline, a yellow crystal at room temperature, has a melting point of 114°C and a boiling point of 306°C. It is slightly soluble in ethanol and diethyl ether, and very insoluble in water.
3. Basic Information on 4-Nitroaniline
4-nitroaniline, the most versatile of the three isomers, appears as a yellow or yellowish-red powder or crystal at room temperature. It has a melting point of 148°C, a boiling point of 332°C, and a density of 1.437 g/mL. It is slightly soluble in ethanol and diethyl ether, and very insoluble in water.
Types of Nitroaniline
Nitroaniline is commonly sold as a reagent for research and development purposes, with 4-nitroaniline being the most common, followed by 2-nitroaniline and 3-nitroaniline. Available volumes include 25 g, 500 g, and other manageable sizes for laboratory use, typically stored at room temperature.
Other Information on Nitroaniline
1. Synthesis of Nitroaniline
4-nitroaniline and 2-nitroaniline can be synthesized from aniline through the following steps:
- Protection of the amino group of aniline with an acetyl group (to produce acetanilide).
- Nitration of the resulting acetanilide with mixed acid (aromatic nucleophilic substitution reaction).
- Purification and separation of 2-nitroacetanilide and 4-nitroacetanilide.
- Deprotection of the acetyl group through hydrolysis.
Due to the ortho-para directing nature of these reactions, 3-nitroaniline cannot be synthesized by this method but can be produced through the nitration of benzamides followed by a Hofmann rearrangement.
2. Chemistry of 4-Nitroaniline
A notable chemical reaction involving 4-nitroaniline is the synthesis of the azo dye Para Red, which is achieved by diazotization of 4-nitroaniline followed by coupling with β-naphthol. For dyeing, the fiber is immersed in an aqueous alkaline solution of β-naphthol before the coupling reaction is conducted on the fiber.