Ortho Nitro Aniline Para Sulphonic Acid
A sulfonated nitroaniline supplied as a water-soluble diazo component for azo dye and reactive dye manufacture.
What is Ortho Nitro Aniline Para Sulphonic Acid?
Ortho Nitro Aniline Para Sulphonic Acid — ONA-PSA — is a yellow to orange crystalline powder carrying an amine, a nitro group beside it, and a sulfonic acid across the ring.
The sulfonic acid group is what distinguishes it from the ordinary nitroaniline colour bases. It makes the molecule and the resulting dye water-soluble, which is what allows the finished colour to be applied from an aqueous dyebath rather than dispersed.
At Chelora Chemicals, ONA-PSA is supplied to a controlled assay with isomer content and free acid specified, giving dye manufacturers reproducible diazotisation and coupling between batches.
- Appearance
- Yellow to orange crystalline powder
- Odour
- Faint, characteristic
- Solubility
- Soluble in water and dilute alkali
- Function
- Water-soluble diazo component
- Grade
- Technical / dye
Formula diagram
Nitroaniline carrying a para sulfonic acid group
- Molecular formulaC6H6N2O5S
- Molecular weight218.19 g/mol
- IUPAC name2-Nitroaniline-4-sulfonic acid
- Functional groupsPrimary aromatic amine, nitro, sulfonic acid
- CAS number616-84-2
Technical product information
Standard specification for Chelora Chemicals' technical and dye grade Ortho Nitro Aniline Para Sulphonic Acid. Custom-grade and bulk specifications are available on request.
| Chemical name | Ortho Nitro Aniline Para Sulphonic Acid |
|---|---|
| Synonyms | ONA-PSA, 2-Nitroaniline-4-sulfonic acid, 4-Amino-3-nitrobenzenesulfonic acid |
| CAS number | 616-84-2 |
| Molecular formula | C6H6N2O5S |
| Molecular weight | 218.19 g/mol |
| Assay (purity) | ≥ 98.0% on dry basis |
| Appearance | Yellow to orange crystalline powder |
| Isomer content | ≤ 1.0% |
| Free sulfuric acid | To agreed specification |
| Moisture | ≤ 1.0% |
| Packaging | 25 kg bags, 500 kg jumbo bags |
| Shelf life | 24 months from date of manufacture |
Applications of Ortho Nitro Aniline Para Sulphonic Acid
Azo dye manufacture
Diazotised as a water-soluble colour component for acid, direct, and reactive dyes.
Reactive dyes
Feeds reactive dye synthesis where aqueous application to cellulosic fibre is required.
Acid dyes
Used in acid dye manufacture for wool, silk, and polyamide.
Dye intermediates
Applied where a sulfonated nitroaniline base is needed for solubility.
Pigment intermediates
Used in laked pigment manufacture where the sulfonate is precipitated as a metal salt.
Specialty chemicals
Applied in sulfonated aromatic derivative synthesis.
Why choose Chelora Chemicals
Every batch of Ortho Nitro Aniline Para Sulphonic Acid is manufactured, tested, and documented to a standard that formulators and process chemists can build on with confidence — from first sample to full production volume.
Consistent purity
Assay controlled at ≥98% on a dry basis with isomer content and free acid verified before dispatch.
Full documentation
COA, SDS, and regulatory data supplied with every shipment.
Flexible volumes
From 25 kg bags to 500 kg jumbo bags and full container loads.
Technical support
Process, handling, and compliance guidance from our chemistry team.
Storage and guidelines
- 01Store in tightly closed original packaging in a cool, dry, well-ventilated store.
- 02Protect from moisture; the product is hygroscopic and cakes as it takes up water.
- 03Keep away from heat, ignition sources, and direct sunlight.
- 04Segregate from strong oxidising agents, strong bases, and reducing agents.
- 05Use acid-resistant equipment; the product is acidic in solution.
- 06Prevent release to drains, surface water, and soil.
Handling precautions
ONA-PSA is harmful if swallowed and causes skin and serious eye irritation. It is for industrial use by trained personnel only.
Nitroanilines can be absorbed through skin and may affect the blood by forming methaemoglobin, though the sulfonic acid group reduces absorption relative to unsulfonated bases.
Control dust during bag emptying, sieving, and charging, and use local exhaust ventilation at all transfer points.
The product stains skin and surfaces strongly; treat any yellow discolouration as evidence of contact and wash immediately.
Refer to the full Safety Data Sheet for exposure limits, spill response, and first-aid measures before use.
Frequently asked questions
What is ONA-PSA used for?
It is a water-soluble diazo component for azo dye manufacture, particularly acid, direct, and reactive dyes applied from aqueous dyebaths.
Why does the sulfonic acid group matter?
It makes the molecule and the finished dye water-soluble. Without it the colour would have to be applied as a dispersion, which limits which fibres and processes it can be used on.
How does it differ from ortho nitroaniline?
ONA is the unsulfonated base, used for pigments and insoluble colours. ONA-PSA carries a sulfonic acid group that makes it and its dyes soluble, so the two serve quite different dye classes.
How is it manufactured?
By sulfonating ortho nitroaniline, or by amination of a sulfonated nitrochlorobenzene. The route affects isomer profile, which is why it is specified.
Does it need a special diazotising agent?
Usually not to the same extent as the unsulfonated nitroanilines. The sulfonic acid group improves aqueous solubility, so conventional sodium nitrite diazotisation is often workable, though weakly basic behaviour still applies.
Is it soluble in water?
Yes, readily, and more so in dilute alkali as the salt. That is the point of the product.
Why is free acid specified?
Residual sulfuric acid from the sulfonation step affects stoichiometry in diazotisation and the pH of the dyebath. Specifying it lets the customer dose accurately.
What purity do you supply?
Standard grade is supplied at a minimum assay of 98% on a dry basis with isomer content at or below 1.0% and moisture at or below 1.0%. Tighter specifications can be produced to order.
What packaging sizes are available?
25 kg bags and 500 kg jumbo bags, with full container loads for bulk users. Samples are available for shade and coupling trials.
Are there regulatory restrictions on azo colourants?
Several jurisdictions restrict azo dyes that can release certain aromatic amines in consumer textiles and leather. Check whether your finished-article market imposes limits before committing to a route using this component.
Do you provide a Certificate of Analysis?
Yes. Every batch is dispatched with a Certificate of Analysis and Safety Data Sheet covering assay on a dry basis, isomer content, free acid, moisture, and appearance.