What Is Phenylenediamine?
Phenylenediamine is an organic compound with two amino groups attached to the benzene ring.
It is represented by the formula C6H4(NH2)2 and has a molecular weight of 108.1. There are three types of positional isomers, depending on the position of the substituent.
The three specific compounds are o-phenylenediamine (1,2-phenylenediamine), m-phenylenediamine (1,3-phenylenediamine), and p-phenylenediamine (1,4-phenylenediamine). Diaminobenzene is also used in some cases.
The CAS registration numbers are 95-54-5 for o-phenylenediamine, 108-45-2 for m-phenylenediamine, and 106-50-3 for p-phenylenediamine.
Uses of Phenylenediamine
1. O-Phenylenediamine
o-phenylenediamine is used as a synthetic precursor for organic compounds, especially heterocyclic compounds. In biochemistry, o-phenylenediamine is used as a coloring reagent in ELISA and other assays in the form of its dihydrochloride salt, taking advantage of its ability to emit fluorescence with an absorption maximum around 492 nm when reacted with peroxidase. In complex chemistry, it is used as an important ligand.
2. M-Phenylenediamine
m-phenylenediamine is used in the preparation of a variety of polymers, such as aramid fibers, epoxy resins, wire enamel coatings, and polyurea elastomers. Other applications include adhesive promoters and dyes for leather and textiles.
3. P-Phenylenediamine
Applications of p-phenylenediamine include polymer materials such as precursors for aramid fibers and plastics, hair dyes, and antioxidants for rubber products. However, since it can cause contact dermatitis as an allergenic substance, other compounds have been used in recent years in many situations regarding hair dyes.
Characteristics of Phenylenediamine
1. O-Phenylenediamine
o-phenylenediamine, as the name “ortho” phenylenediamine implies, is a compound in which the first and second positions of the benzene ring are replaced by amino groups. It has a melting point of 102-104°C, a boiling point of 252°C, a density of 1.031 g/cm3, and is a white or brown powder at room temperature.
2. M-Phenylenediamine
As the name “meta” phenylenediamine suggests, m-phenylenediamine is a compound in which the 1- and 3-positions of the benzene ring are replaced by amino groups. It has a melting point of 64-66°C, a boiling point of 282-284°C, a density of 1.14 g/cm3, and is a light gray flaky solid at room temperature.
Synthetically, it can be obtained by nitration of benzene to obtain 1,3-dinitrobenzene, followed by hydrogenation reduction.
3. P-Phenylenediamine
As the name “para” phenylenediamine suggests, p-phenylenediamine is a compound in which the 1- and 4-positions of the benzene ring are replaced by amino groups. It has a melting point of 145-147°C, a boiling point of 267°C, and a density of 0.72 g/cm3. It is a white solid at room temperature, but turns dark upon air oxidation.
Other methods used industrially are the conversion of aniline to diphenyltriazine to obtain 4-aminoazobenzene by acid catalysis, followed by hydrogenation to obtain p-phenylenediamine.
Types of Phenylenediamine
As noted in the introduction, there are three types of positional isomers of phenylenediamine. All compounds are commonly sold as reagent products for research and development; they are available in different volumes such as 5g, 25g, 100g, and 500g and are reagents that may be handled at room temperature or stored under refrigeration.
Phenylenediamine is also sold as a dye product because of its use as a hair color dye intermediate.