Para Nitrotoluene Ortho Sulphonic Acid
A high-purity sulfonated nitrotoluene, supplied as 4-nitrotoluene-2-sulfonic acid for the stilbene optical brightener route and sulfonated dye chemistry.
What is PNT-OSA?
PNT-OSA, formally 4-nitrotoluene-2-sulfonic acid, is an off-white to pale yellow crystalline solid made by sulfonating para nitrotoluene. It carries a methyl group at C-1, a sulfonic acid group beside it at C-2 and a nitro group at C-4.
It is the first committed step of the optical brightener chain. Treated with alkali under oxidising conditions, two molecules join through their methyl groups to give a dinitrostilbene disulfonic acid; reduce that and you have DASDA, the diaminostilbene core that sits inside most of the fluorescent whitening agents used in detergents, paper and textiles. The sulfonic acid group is what keeps the whole chain water soluble.
At Chelora Dyes, PNT-OSA is supplied as dried powder, as the sodium salt or as an aqueous paste, with assay quoted on a dry basis and insoluble matter held low so the coupling step downstream runs cleanly.
- Appearance
- Off-white / pale yellow
- Odour
- Faint, characteristic
- Solubility
- Water, dilute alkali
- Function
- Sulfonated intermediate
- Grade
- Powder / salt / paste
Nitrotoluene ring with an ortho sulfonic acid group
- Molecular formulaC7H7NO5S
- Molecular weight217.20 g/mol
- IUPAC name4-Nitrotoluene-2-sulfonic acid
- Functional groupsSulfonic acid, nitro, methyl
- CAS number121-03-9
Technical product information
Standard specification for Chelora Dyes' powder grade PNT-OSA. Sodium salt, paste and solution grades are available to alternative specifications on request.
| Chemical name | Para Nitrotoluene Ortho Sulphonic Acid |
|---|---|
| Synonyms | 4-Nitrotoluene-2-sulfonic acid, PNT-OSA, PNTSA |
| CAS number | 121-03-9 |
| Molecular formula | C7H7NO5S |
| Molecular weight | 217.20 g/mol |
| Assay (dry basis) | ≥ 90.0% |
| Appearance | Off-white to pale yellow crystalline powder |
| Thermal behaviour | Decomposes on heating; no sharp melting point |
| Moisture content | ≤ 1.0% (powder grade) |
| Insoluble matter | ≤ 0.5% |
| pH (1% aqueous solution) | 1.0–2.5 |
| Solubility | Freely soluble in water and dilute alkali |
| Available forms | Powder, sodium salt, aqueous paste or solution |
| Packaging | 25 kg / 50 kg lined bags or drums, 500 kg jumbo bags; IBCs for liquid grades |
| Shelf life | 24 months in sealed original packaging |
Applications of PNT-OSA
Optical brightener route
Oxidative coupling and reduction give the diaminostilbene disulfonic acid core of stilbene brighteners.
Detergent whiteners
Feeds the fluorescent whitening agents used across laundry powders and liquid detergents.
Paper and textile brighteners
Supplies brightener intermediates for paper coating, board and textile finishing systems.
Direct and reactive dyes
Used as a water-soluble sulfonated intermediate in dye synthesis and stilbene direct dyes.
Fine chemical intermediates
Reduction and substitution chemistry give access to related sulfonated anilines.
Research and pilot supply
Available in drum quantities for process development and pilot-scale brightener trials.
Why choose Chelora Dyes
Consistent purity
Assay controlled on a dry basis with insoluble matter and colour verified before dispatch.
Full documentation
COA, SDS, and regulatory data supplied with every shipment.
Choice of form
Powder, sodium salt or paste, matched to how your plant charges it.
Technical support
Coupling, reduction, and compliance guidance from our chemistry team.
Storage and guidelines
- Store in tightly sealed original packaging in a cool, dry, well-ventilated store.
- Keep dry — the material is hygroscopic and will cake if exposed to humid air.
- Segregate from alkalis, strong oxidising agents and reactive metals.
- Use acid-resistant lined or plastic containers; avoid bare mild steel.
- Re-seal bags promptly after use to preserve moisture and assay specification.
- Contain spillage and neutralise carefully before disposal; keep out of drains.
Handling precautions
PNT-OSA is a strong organic acid. It causes serious eye damage and can burn skin on contact, and contact with alkalis liberates heat.
As a nitroaromatic it is also harmful if swallowed or inhaled, and dust should be controlled at weighing and charging points.
Use acid-resistant gloves, full face or chemical splash goggles and protective clothing, with local exhaust ventilation wherever dust or mist may be generated. Have eyewash and shower facilities available at the point of use.
Refer to the full Safety Data Sheet for exposure limits, spill neutralisation, disposal and first-aid measures before any handling operation.
Frequently asked questions
What is PNT-OSA used for?
It is the entry point to the stilbene optical brightener chain. Oxidative coupling in alkali joins two molecules through their methyl groups to give the dinitrostilbene disulfonic acid, which is then reduced to the diaminostilbene disulfonic acid that forms the core of most fluorescent whitening agents for detergents, paper and textiles. It is also used as a sulfonated intermediate in dye manufacture.
Why is the sulfonic acid group needed?
It makes the molecule and everything built from it water soluble, which is essential for a brightener that has to be applied from an aqueous detergent or paper coating system. It also directs the chemistry and improves the substantivity of the finished product on fibre.
In what forms is it supplied?
As a dried powder, as the sodium salt, and as an aqueous paste or solution for users who prefer to charge it wet. Assay is quoted on a dry basis in each case, so specify the form you need when ordering.
Is PNT-OSA soluble in water?
Yes, freely. As a sulfonic acid it dissolves readily in water and in dilute alkali as the salt, which is why the coupling step downstream is run directly in an aqueous alkaline medium.
What purity do you supply?
Standard grade is supplied at a minimum assay of 90% on a dry basis, with insoluble matter and moisture held within tight limits. Higher assay grades can be manufactured to order for brightener applications where colour is critical.
What packaging sizes are available?
25 kg and 50 kg HDPE-lined bags or fibre drums for powder, 500 kg jumbo bags for bulk, and lined drums or IBCs for paste and solution grades.
How should it be stored, and for how long?
In sealed original packaging in a cool, dry, ventilated store away from alkalis and strong oxidisers. The material is hygroscopic and strongly acidic, so keep it dry and away from bare metal. Shelf life is 24 months from manufacture when storage conditions are maintained.
Is it hazardous to handle?
Yes. It is a strong organic acid that causes serious eye damage and skin burns, and as a nitroaromatic it is harmful if swallowed or inhaled. Use acid-resistant gloves and full eye protection, control dust, and review the current Safety Data Sheet before any handling operation.
