Para Nitro Toluene Ortho Sulphonic Acid
A sulfonated nitroaromatic supplied as the entry point to stilbene chemistry and the optical brightener chain.
What is Para Nitro Toluene Ortho Sulphonic Acid?
Para Nitro Toluene Ortho Sulphonic Acid — PNT-OSA — is a light yellow to buff solid, commonly supplied as a paste or solution. It is made by sulfonating para nitrotoluene, which places the sulfonic acid group ortho to the methyl.
It sits at the head of one of the most important chains in the colour industry. Oxidative coupling of two molecules gives the dinitrostilbene disulfonic acid known as DNS acid, and reducing that gives DAS acid — the backbone of virtually every stilbene optical brightener used in detergents, paper, and textiles.
At Chelora Chemicals, PNT-OSA is supplied to a controlled assay with isomer content and free acid specified, since both carry directly into the efficiency of the oxidative coupling step downstream.
- Appearance
- Light yellow to buff solid, paste, or solution
- Odour
- Faint, characteristic
- Solubility
- Soluble in water and dilute alkali
- Function
- Chemical intermediate
- Grade
- Technical
Formula diagram
Nitrotoluene carrying a sulfonic acid group
- Molecular formulaC7H7NO5S
- Molecular weight217.20 g/mol
- IUPAC name4-Nitrotoluene-2-sulfonic acid
- Functional groupsSulfonic acid, nitro, alkyl
- CAS number121-03-9
Technical product information
Standard specification for Chelora Chemicals' technical grade Para Nitro Toluene Ortho Sulphonic Acid. Custom-grade and bulk specifications are available on request.
| Chemical name | Para Nitro Toluene Ortho Sulphonic Acid |
|---|---|
| Synonyms | PNT-OSA, PNTOSA, 4-Nitrotoluene-2-sulfonic acid, NTS acid |
| CAS number | 121-03-9 |
| Molecular formula | C7H7NO5S |
| Molecular weight | 217.20 g/mol |
| Assay (purity) | ≥ 98.0% on dry basis |
| Appearance | Light yellow to buff solid, paste, or solution |
| Form supplied | Solid, paste, or solution — specify on enquiry |
| Isomer content | ≤ 1.0% |
| Free sulfuric acid | To agreed specification |
| Packaging | 25 kg bags, 200 kg drums, IBC for solution |
| Shelf life | 12 months in sealed original packaging |
Applications of Para Nitro Toluene Ortho Sulphonic Acid
Optical brightener chain
Oxidatively coupled to DNS acid and reduced to DAS acid, the core of stilbene fluorescent whitening agents.
Stilbene dye intermediates
Feeds the manufacture of direct and reactive stilbene dyes.
Detergent brighteners
Supports the fluorescent whitening agents used across laundry detergent formulation.
Paper & textile brighteners
Underpins whitening agents for paper coating and textile finishing.
Dye intermediates
Used where a water-soluble sulfonated nitroaromatic is required.
Specialty chemicals
Applied in the synthesis of sulfonated aromatic derivatives.
Why choose Chelora Chemicals
Every batch of Para Nitro Toluene Ortho 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 drums and IBC solution supply.
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; solid grades are hygroscopic and cake as they take up water.
- 03Keep solution and paste grades from freezing, and homogenise before use if separation occurs.
- 04Segregate from strong oxidising agents, strong bases, and reducing agents.
- 05Use acid-resistant containers and equipment; the product is acidic in solution.
- 06Prevent release to drains, surface water, and soil.
Handling precautions
PNT-OSA is harmful if swallowed and causes skin and serious eye irritation. It is for industrial use by trained personnel only.
The material is acidic in solution and can cause burns on prolonged contact. Chemical-resistant gloves, coveralls, and eye protection are required.
Control dust with solid grades during bag emptying and charging, and use local exhaust ventilation at transfer points.
Nitroaromatics can decompose exothermically if overheated. Drying and any heated processing require temperature control and a documented thermal assessment.
The oxidative coupling step downstream is exothermic and requires its own process risk assessment.
Refer to the full Safety Data Sheet for exposure limits, spill response, and first-aid measures before use.
Frequently asked questions
What is PNT-OSA used for?
Almost entirely as the starting material for optical brighteners. It is oxidatively coupled to DNS acid and then reduced to DAS acid, which is the core of stilbene fluorescent whitening agents used in detergents, paper, and textiles.
How is it manufactured?
By sulfonating para nitrotoluene with oleum or sulfuric acid. The methyl group directs the sulfonic acid to the position ortho to it, giving the 2-sulfonic acid on a 4-nitrotoluene skeleton.
What are DNS acid and DAS acid?
DNS acid is the dinitrostilbene disulfonic acid formed by oxidatively coupling two PNT-OSA molecules. Reducing its nitro groups gives DAS acid, the diaminostilbene disulfonic acid that virtually all stilbene brighteners are built from.
What form is it supplied in?
Solid, paste, or solution depending on your process. Specify the form and concentration on enquiry, since handling, packaging, and the way assay is reported all differ.
Why does the sulfonic acid group matter?
It makes the molecule and everything built from it water-soluble. Optical brighteners have to work in aqueous detergent and paper systems, so solubility is a functional requirement rather than a convenience.
Why is isomer content specified?
Isomeric sulfonic acids carry through the coupling step and produce brighteners with different fluorescence and substantivity. Controlling them at this stage protects the performance of the finished whitening agent.
Is it soluble in water?
Yes, readily, and more so in dilute alkali as the salt. That solubility is what makes the whole downstream chain work.
What purity do you supply?
Standard technical grade is supplied at a minimum assay of 98% on a dry basis with isomer content at or below 1.0%. Free acid content is set against your process requirement.
What packaging is available?
25 kg bags and 200 kg drums for solid grades, and IBCs for solution grades. Samples are available for coupling trials.
How should it be stored?
Cool, dry, and sealed. Solid grades are hygroscopic and cake if they take up moisture; solution grades should be protected from freezing and homogenised if they separate.
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.