5-Chloro-2-methyl-4-nitroaniline (CAS 13852-51-2) is a multi-substituted aromatic amine: one benzene ring carrying an amino group at position 1, a methyl group at position 2, a nitro group at position 4 and a chlorine atom at position 5. The substitution pattern is deliberate. The amino group is the reactive handle for diazotisation and coupling, the nitro group is strongly electron-withdrawing and shifts light absorption into the visible region, the chlorine improves the shade and fastness of the colourants built from it, and the methyl group fine-tunes steric and electronic effects. Together they make the compound a versatile intermediate for colorants, fine chemicals and crop protection chemistry.
Identity and Structural Profile
| Parameter | Typical value |
|---|---|
| CAS number | 13852-51-2 |
| Molecular formula | C7H7ClN2O2 |
| Molar mass | about 186.6 g/mol |
| Appearance | yellow to orange crystalline powder |
| Melting range | approximately 165-168 C |
| Water solubility | sparingly soluble |
| Organic solubility | soluble in ethanol, acetone and chloroform |
| Reactive sites | amino group for diazotisation and acylation; nitro group for reduction |
Dye and Pigment Synthesis
The primary industrial use is in azo colorants. Treatment of the amino group with nitrous acid generates a diazonium salt, which is then coupled onto naphthol, pyrazolone or similar coupling components to build the coloured molecule. Because the ring already carries a nitro group and a chlorine atom, the resulting dyes and pigments deliver strong yellow, orange and red shades with good colour strength and light fastness.
These colorants are used in textile dyeing and printing, leather finishing, printing inks and the mass colouring of plastics, where the chlorine substituent helps the shade resist fading and improves fastness to washing and light.
Pharmaceutical and Fine Chemical Intermediates
Reduction of the nitro group turns the molecule into an aromatic diamine carrying two differently substituted amine positions, a useful scaffold for building nitrogen heterocycles such as benzimidazoles and quinoxalines. Medicinal chemistry programmes also use substituted nitroanilines as fragments in antibacterial and antiparasitic series, where the nitro group contributes to binding interactions with the biological target and the chlorine atom adjusts the electronic character of the ring.
Agrochemical Intermediates
Herbicide and insecticide manufacture makes use of the same reactivity. The nitro group contributes to biological activity by interacting with enzymes in the target organism, while the chlorine improves chemical stability under field conditions, so derivatives of the compound are used as building blocks for selected herbicide and insecticide families. Intermediates of this type are handled in closed systems because the electron-poor ring makes them reactive towards nucleophiles as well as electrophiles.
Organic Synthesis and Laboratory Applications
With four different substituents on one ring, the molecule is a useful model substrate for studying how electron-withdrawing groups influence diazotisation, coupling and nucleophilic aromatic substitution. Research laboratories use it to compare reaction rates and selectivity against simpler anilines, and to prepare reference compounds for analytical method development in colorant and agrochemical testing.
Purity Control, Packaging and Safe Handling
Quality control of this intermediate normally combines assay by high performance liquid chromatography or gas chromatography with area normalisation, amine content by diazotisation titration, moisture by Karl Fischer titration following ASTM E203, and checks on appearance, melting range and insoluble matter. Commercial grades are typically 99 percent or higher, with additional limits on positional isomers where colour shade consistency matters.
The product is packed in 25 kg fibre drums or larger woven bags with inner polyethylene liners to keep moisture and light out, and stored in a cool, dry, well-ventilated place below 25 C away from strong oxidising agents. As with other nitro-substituted aromatic amines, the material is regarded as harmful if swallowed and as an irritant, so dust should be controlled by closed transfer and local exhaust ventilation, and operators should wear chemical gloves, goggles and dust protection. Strong oxidisers and strong acids must be kept away from storage and handling areas.
Frequently Asked Questions
Q: What is 5-chloro-2-methyl-4-nitroaniline used for?
It is an intermediate for azo dyes and organic pigments, a building block for pharmaceutical and agrochemical synthesis, and a model substrate for studying aromatic amine chemistry.
Q: What is the CAS number of 5-chloro-2-methyl-4-nitroaniline?
The CAS registry number is 13852-51-2, with molecular formula C7H7ClN2O2 and a molar mass of about 186.6 g/mol.
Q: How is the compound converted into azo dyes?
The amino group reacts with nitrous acid to form a diazonium salt. That salt is then coupled with a naphthol, pyrazolone or similar component to form the azo colourant, giving yellow, orange and red shades.
Q: What is the melting point of this intermediate?
The melting range is approximately 165-168 C, and it is normally supplied as a yellow to orange crystalline powder that melts to a clear liquid over that interval.
Q: How should 5-chloro-2-methyl-4-nitroaniline be stored?
Keep it in a cool, dry, well-ventilated store below 25 C in sealed, light-proof packaging, separated from strong oxidisers and strong acids, and away from sources of ignition.
Q: Is the compound soluble in water?
It is only sparingly soluble in water, but it dissolves readily in polar organic solvents such as ethanol, acetone and chloroform, which is how it is normally charged into diazotisation and coupling reactions.