Para Nitrotoluene Ortho Sulphonic Acid
Sulphonating para nitrotoluene does two things at once. It makes the molecule water soluble, and it activates the methyl group so that two molecules will couple to each other head to head in hot alkali. That coupling is the stilbene bond — and every optical brightener in the paper, detergent and textile industries is built on it.
Chelora Chemicals supplies PNTOSA as an aqueous solution, a wet paste or the sodium salt to optical brightener and dye producers worldwide, in acid-resistant packing, with a batch COA and GHS safety data sheet on every consignment.
Product identity
- CAS Number
- 121-03-9
- IUPAC name
- 4-Nitrotoluene-2-sulphonic acid
- Molecular formula
- C7H7NO5S
- Molecular weight
- 217.20 g/mol
- EC / EINECS
- 204-442-3
- UN Number
- 3265 · Class 8*
- SMILES
- Cc1ccc(cc1S(=O)(=O)O)[N+](=O)[O-]
- HS Code
- 2904 10**
* The transport entry depends on the form you buy — solution grades normally travel as a corrosive liquid, solid and salt grades under the corresponding solid entry. ** Confirm the exact HS heading with your customs broker; sulphonated nitro derivatives can sit under a different subheading depending on the destination tariff schedule.
What PNTOSA is used for
Para Nitrotoluene Ortho Sulphonic Acid is a pale yellow to light brown aqueous solution or crystalline solid, made by sulphonating para nitrotoluene with oleum and isolating the 2-sulphonic acid. Almost the entire commercial demand runs through one reaction, and that reaction is the reason the molecule is sulphonated at all.
In hot sodium hydroxide with air or hypochlorite as the oxidant, two PNTOSA molecules couple through their methyl groups to give DNS acid — 4,4'-dinitrostilbene-2,2'-disulphonic acid. Reduce the two nitro groups and you have DAS, 4,4'-diaminostilbene-2,2'-disulphonic acid. Condense DAS with cyanuric chloride and a pair of amines and you have a triazinyl stilbene optical brightener — the whitening agent in printing paper, laundry detergent and textile finishing. A smaller stream goes into direct dyes where the stilbene backbone itself provides the chromophore.
Why it has to be sulphonated first
- Solubility. The coupling runs in strong aqueous alkali. Unsulphonated para nitrotoluene would simply sit as a separate phase and never react usefully.
- Activation. The sulphonic acid group ortho to the methyl, working with the para nitro group, makes the methyl hydrogens acidic enough to be pulled off and coupled.
- It stays in the product. The two sulphonate groups survive into DNS, into DAS and into the finished brightener, where they are what makes the brightener water soluble and substantive to cellulose fibre.
- Position matters. Sulphonation at the 2-position is what the chemistry needs. Isomeric sulphonic acids are dead weight that consume alkali and oxidant without producing stilbene. See the para nitrotoluene page.
On this product the number that matters is not gross weight but kilograms of active. Always state the strength basis on your purchase order — see the full intermediate range.
Appearance and handling character
Solution grades ship as a mobile, strongly acidic liquid that can deposit crystals below roughly 10 °C; paste grades are a thick, pumpable slurry; the sodium salt is a free-flowing powder. All three are corrosive — the hazard here is a chemical burn and attack on unlined steel, not the systemic toxicity that dominates the nitroaromatics it is made from. The safety section below should be read before any handling is planned.
| Parameter | Typical value |
|---|---|
| Appearance | Pale yellow to light brown solution |
| Strength as free acid | 65% ± 2% |
| Purity, dry basis | 98.0% min |
| Free sulphuric acid | Reported per batch |
| Isomeric sulphonic acids | Reported per batch |
| Unsulphonated PNT | Reported per batch |
| Iron (as Fe) | Low — reported per batch |
Important: the figures above are indicative of commercial grade material and are offered for planning only. The batch certificate of analysis is the governing document. On this product the strength figure decides what you actually pay per kilogram of active — tell us the basis you buy on and we will quote against it rather than against gross weight.
| Property | Value |
|---|---|
| Physical state | Solution, paste or crystalline solid |
| Melting point, free acid | ≈ 103 – 104 °C |
| Water solubility | Freely soluble |
| pH of solution | Strongly acidic, < 1 |
| Relative density, 65% solution | ≈ 1.3 – 1.4 |
| Crystallisation on cooling | Possible below ≈ 10 °C |
| Action on metals | Corrosive to unlined mild steel |
| Key reaction | Oxidative coupling in NaOH → DNS acid |
Physical constants compiled from public reference data for CAS 121-03-9 and rounded for readability. Treat them as orientation, not as a specification.
Where our customers put this molecule to work
One chain dominates. The interest lies in how far down it a given buyer operates — some stop at DNS acid, some run through to the finished brightener.
DNS acid manufacture
Oxidative coupling in sodium hydroxide joins two molecules at the methyl carbon to give 4,4'-dinitrostilbene-2,2'-disulphonic acid — the step that creates the stilbene double bond and the reason this intermediate exists commercially.
- Alkaline oxidative coupling route
- Isomer content lowers yield directly
- See our intermediate range
DAS and stilbene brighteners
Reduction of DNS acid gives DAS, which is condensed with cyanuric chloride and amines into the triazinyl stilbene brighteners that whiten paper, detergent powders and textile goods — the largest single outlet for this chain.
- Paper, detergent and textile grades
- Shade sensitive to iron and isomers
- Technical desk review of your route
Paper mill whitening chains
Paper-grade brighteners are bought by tonnage and judged on whiteness at the reel. Mills that integrate backwards into brightener manufacture buy this intermediate directly rather than the finished product.
- Bulk solution and IBC supply
- Contracted call-off against campaigns
- Price held across the contract period
Direct dye synthesis
The stilbene backbone is itself a chromophore. A smaller but steady stream of demand goes into direct yellow and orange dyes for cellulosic fibre and for paper dyeing.
- Direct dye intermediate routes
- Shade sensitive to feed purity
- See our dye intermediate range
Laboratory & reference use
Small quantities serve as reference standards and in method development for sulphonic acid assay and isomer determination — a genuine analytical problem where strength and isomer profile both have to be measured.
- Reference-grade material on request
- Small corrosive-compliant packs
- Full analytical documentation available
Contract & scheduled supply
Sulphonation plants run this product to campaign, not continuously. Most buyers want tonnage released against a production plan rather than in one shipment. We hold inventory and release it to your schedule.
- Annual contracts with scheduled call-off
- Quoted per kilogram of active
- Second source held in reserve
How we supply PNTOSA
Chelora Chemicals is a supplier and sourcing partner, not a manufacturer. On a product sold in three different physical forms at three different strengths, owning no plant means we can route your order to the producer whose form and strength actually suit your charging arrangement instead of persuading you to take what a captive unit makes.
We place your order with whichever qualified producer best matches your strength, your iron ceiling, your price point and your delivery window.
We keep a second qualified source on this line. When a sulphonation campaign slips, your brightener run switches source rather than stalling.
- Quoted per kilogram of active. Solution, paste and salt are not comparable on gross weight, and comparing them that way is where buyers on this product lose money.
- Iron reported, not assumed. It appears as its own figure on the COA, because it carries straight through to the whiteness of your finished brightener.
- Batch COA shared before dispatch. You approve strength, purity, free acid and iron against your own spec while the material is still in our warehouse.
- Corrosivity stated up front. Containment and pump materials have to be right before the first drum lands, so we raise it at enquiry stage rather than on the delivery note.
- Pre-shipment samples for qualification. New account or new source, your laboratory runs a coupling trial before the full quantity ever moves.
- Export machinery handled in-house. Class 8 classification, approved packing, labelling, freight booking and customs paperwork are ours to manage.
Packed the way your plant receives it
Form and pack format drive your landed cost per kilogram of active. Tell us how the material will be charged at your end and we will quote the format that suits your operation.
HDPE & lined drums
Acid-resistant drums for solution and paste grades — the standard commercial format and the easiest to handle without dedicated bulk receipt facilities.
IBC
Composite IBC for solution grade where you pump directly into the coupling vessel — fewer handling operations and less chance of a drum-decanting spill.
Bags — sodium salt
Lined bags or fibre drums for the dry sodium salt, where you would rather not pay freight on water or where winter crystallisation rules out liquid supply.
Samples & trial packs
Laboratory and pilot quantities dispatched so your R&D team can run a coupling trial first — subject to corrosive-cargo rules for your destination and courier.
Incoterms to suit you
Quoted on the Incoterm your purchasing team works to, with Class 8 documentation filed before the booking is made rather than chased afterwards.
Crystallisation management
Solution grade can drop crystals in a cold container or an unheated yard. For winter destinations we will advise on sheltered storage, heated discharge or switching to the salt.
This one burns — corrosivity is the controlling hazard
Unlike the nitroaromatics it is made from, PNTOSA's defining hazard is not systemic toxicity but chemical burns and attack on materials. It causes severe skin burns and serious eye damage, and it corrodes unlined mild steel. The summary below is orientation only — the safety data sheet supplied with your consignment is the authoritative document.
Classified hazards
H314Causes severe skin burns and eye damage.H318Causes serious eye damage.H290May be corrosive to metals.H335May cause respiratory irritation.H302Harmful if swallowed.H412Harmful to aquatic life with long lasting effects.
Hazard statements reflect classifications commonly published for CAS 121-03-9 and may vary with the form and strength supplied. Residual free sulphuric acid in solution grades contributes to the corrosive classification. Always read the SDS issued with your specific batch.
Spill & emergency orientation
Plan your response before the drum arrives. Sections 4, 5 and 6 of the SDS are the authoritative instructions and should be posted at the point of use.
- Eyes are the emergency. H318 applies — immediate, prolonged irrigation with an eyewash that actually reaches the point of use, and medical attention regardless of how the casualty feels.
- Neutralise carefully, not quickly. Absorb the spill with inert material first, then neutralise with soda ash or lime. Neutralising a pooled acid directly generates heat and spatter.
- Never add water to concentrated acid. Dilution is exothermic — add acid to water, never the reverse, and never inside the spill area.
- Segregate from alkalis, cyanides, sulphides and metals. Contact with alkali is violently exothermic; contact with mild steel generates hydrogen.
- Contain, do not flush to drain. H412 applies and the pH alone will breach most discharge consents. Collect and dispose of as regulated chemical waste.
Storage
- Acid-resistant containment only. Lined steel, HDPE or glass-reinforced plastic. Unlined mild steel will corrode, and the iron it releases ends up in your brightener.
- Bunded, well-ventilated store with the bund sized for the largest container and built of materials the acid will not attack.
- Plan for cold. Solution grades can deposit crystals below roughly 10 °C. Sheltered or heated storage avoids a drum that has to be re-dissolved before use.
- Segregate from alkalis, oxidisers and reactive metals in storage as well as in process.
- Shelf life is typically 12 months or more in sealed original packing. Re-assay strength before use after long storage — the number you charge against must be current.
Handling & PPE
- Design splash contact out. Closed transfer, dedicated acid-rated pumps and hoses, and a charging arrangement that does not require anyone to lean over an open vessel.
- Face shield over goggles, acid-resistant gloves, apron and boots for any decanting or sampling operation. Chemical goggles alone are not enough against a pressurised line.
- Eyewash and safety shower within unobstructed reach of every transfer point, tested on a schedule rather than on paper.
- Respiratory protection where mist or vapour can be generated during hot transfer or during the coupling charge, per your own exposure assessment.
- Never discharge to drain or watercourse. Contain and dispose of as regulated chemical waste.
Transport
PNTOSA moves as regulated corrosive cargo — solution grades normally under UN 3265, Class 8, solid and salt grades under the corresponding solid entry. We classify each consignment against the form and strength actually shipped, apply approved packaging and labelling, and file the dangerous-goods declaration before the booking is made. The applicable packing group is stated on your shipping documents and SDS — ask us for the current DG paperwork when you plan the shipment.
What travels with every consignment
A chemical shipment is only as good as the file that travels with it. Verifying what the source plant sends is precisely the work you are buying from a supplier.
Certificate of Analysis
Batch-specific strength, purity on dry basis, free sulphuric acid, isomeric sulphonic acids, unsulphonated PNT and iron — checked against your purchase specification before release.
GHS Safety Data Sheet
Full 16-section SDS in GHS format covering hazards, exposure controls, handling, storage, spill response, materials compatibility and disposal — issued in the language your destination requires.
Dangerous Goods Declaration
Correct UN entry for the form shipped, hazard class, packing group and IMDG or IATA declaration prepared and filed before the container is booked, with correctly marked packaging.
Certificate of Origin
Chamber-attested where required, plus preferential-origin forms where a trade agreement gives your import duty relief at the destination.
Third-party inspection
SGS, Intertek or Bureau Veritas sampling and inspection arranged on request before loading, giving you independent verification of strength and quantity actually shipped.
Retained & pre-shipment samples
Pre-shipment samples carry the same COA as the commercial lot, so what your laboratory couples is exactly what arrives. Retention samples held against the batch.
Two molecules in, one stilbene out
This is one of the few intermediates whose entire commercial purpose is a coupling with itself. The routes below are the general industrial pattern, not a process disclosure.
Sulphonate the PNT
Para nitrotoluene is sulphonated with oleum at the 2-position. Strength, free acid and isomer content on your COA all trace to how tightly this step was run.
Isolate as acid or salt
The product is taken off as an aqueous solution, a paste, or salted out and dried as the sodium salt — three forms of the same active molecule.
Couple in alkali to DNS
Hot sodium hydroxide with air or hypochlorite joins two molecules through the methyl carbons, forming the stilbene double bond and giving DNS acid.
Reduce to DAS, then brighten
Reduction gives DAS; condensation with cyanuric chloride and amines gives the triazinyl stilbene brightener that whitens paper, detergent and textile goods.
Why feed quality carries through the whole route
In brightener chemistry an impurity does not simply dilute the product — it consumes reagent and shows up in the whiteness:
- Isomeric sulphonic acids cannot couple productively. They absorb alkali and oxidant, lower your DNS yield and leave coloured by-products behind. This is the single most consequential impurity on the product.
- Unsulphonated para nitrotoluene is insoluble in the coupling medium — it phases out, fouls the vessel and reports as loss. See the PNT page.
- Free sulphuric acid consumes caustic before any coupling begins, so a high figure quietly raises your alkali bill on every batch.
- Iron carries forward into DNS and DAS and dulls the finished white — which is why containment material is a quality question on this product, not just a safety one.
That is why we quote against your written strength and iron limit rather than a generic "technical" grade, and why the batch COA is shared for approval before dispatch rather than sent with the invoice.
| Stage | What it becomes |
|---|---|
| Para Nitrotoluene CAS 99-99-0 | Sulphonated to PNTOSA |
| PNTOSA CAS 121-03-9 — this product | DNS acid Oxidative coupling |
| DNS acid | DAS Reduction |
| DAS | Triazinyl stilbene brighteners Paper, detergent, textile |
We supply across the nitrotoluene and sulphonation chain — see the full intermediate range, including Oleum 23% for the sulphonation step itself.
What actually moves the price of this intermediate
Knowing what drives the quote helps you time a purchase and read whether an offer is realistic.
You are buying water as well
A 65% solution is 35% freight you do not want. Whether solution or salt is cheaper depends almost entirely on how far the material has to travel — which is why the two forms swap places on landed cost at different distances.
- Always compare per kilogram of active
- Long haul favours the salt
- We will run both numbers for you
Upstream feedstock
The route runs back through toluene, nitration to the nitrotoluene isomers, separation of the para isomer and sulphonation with oleum. Toluene, nitric acid and sulphur economics all feed through within a quarter or so.
- PNT availability sets the floor
- Oleum cost moves with sulphur
- We flag feedstock-driven moves in the quote
Campaign scheduling
Sulphonation units run this product in campaigns between other sulphonations. Buying outside a campaign window means paying for a dedicated run or waiting for the next one.
- Campaign dates drive lead time
- Ask us when the next run is scheduled
- Contracted call-off smooths the exposure
Effluent & spent acid
Sulphonation generates spent acid and a salt-laden effluent stream, and the cost of handling both sits inside the price. Tightening discharge rules have closed smaller units and concentrated capacity.
- Effluent rules shape plant economics
- Fewer units means thinner supply
- We check destination rules before quoting
Freight & corrosive surcharges
Class 8 liquid cargo carries a hazardous surcharge and some lanes restrict IBC movement. Destination and Incoterm move landed cost as much as the ex-works price does.
- Compare on landed cost, not ex-works
- IBC is not accepted on every lane
- We quote FOB, CIF, CFR or DDP as you prefer
Brightener demand cycle
Demand tracks paper production and detergent output. A strong season at the mills tightens this intermediate several months before it shows in the brightener price.
- Paper and detergent cycles lead the price
- We hold a second qualified source
- Ask us about dual-source contracts
| If your end use is… | Specify |
|---|---|
| Paper-grade brightener chain | Low iron; tight isomer ceiling; bulk solution or IBC |
| Detergent-grade brightener | Consistent strength; low free sulphuric acid |
| Textile brightener | Low iron for shade control; full impurity profile |
| Direct dye synthesis | Isomer limit; low unsulphonated PNT |
| Long-haul or cold destination | Sodium salt grade rather than solution |
| Laboratory / reference | Highest available purity, small corrosive-compliant pack |
Not sure which row you are in? Describe what you make from it and our technical desk will recommend the form and grade — including telling you when a cheaper specification would do the job just as well.
Support that goes beyond shipping the drum
What our technical desk will do
- Settle the form and the basis first. Solution, paste or salt, and at what strength — on this product that is where quotes stop being comparable, and we fix it in the first reply.
- Set the iron ceiling with you. It is the number that decides whether your finished brightener looks white or grey, and the one most often left off a purchase order.
- Be straight about the corrosivity. Containment, pump and gasket materials have to be right before the first delivery, so we state it at enquiry stage.
- Review your specification before it goes into a contract, so you are not locked into a limit that no sulphonation plant can consistently hit.
Regulatory & compliance notes
- Corrosive storage obligations are jurisdiction-specific. Bunding, material compatibility and emergency equipment requirements differ. Confirm what applies at your site before the first delivery.
- Import controls vary by destination. We check the destination rules before quoting, not after you have raised the PO.
- Chemical inventory listings differ between regions — we will supply the identity data you need for that filing.
- Effluent and pH consents matter on this product. Check your discharge consent against both the acidity and the organic load before introducing it.
None of the above is legal advice — your own regulatory affairs team owns the final compliance position for your import and your workplace. What we commit to is accurate product identity data, an honest statement of the hazard classification and complete documentation to work from.
From enquiry to delivered pallet
Send the specification
Product name or CAS 121-03-9, the form you need, your strength basis, iron and isomer limits, quantity, pack preference and destination port.
Receive a firm quote
Pricing per kilogram of active, lead time, packing and Incoterm confirmed in writing within 24 hours — our sourcing desk is staffed around the clock.
Qualify and approve
Sample dispatched if you are qualifying a new source. Batch COA shared for your approval before the material is released.
Ship and track
Class 8 classification filed, corrosive freight booked, export documents issued, and the consignment tracked through transit and clearance to your plant.
Others in the Chelora range
What buyers ask us about PNTOSA
What form is PNTOSA normally supplied in?
What strength and purity do you normally supply?
Why does PNTOSA matter to a brightener producer?
What does the iron figure actually affect?
What is the minimum order quantity?
How long does delivery take?
How should we store it, and what is the shelf life?
Is this a dangerous good? What paperwork comes with it?
- Batch certificate of analysis
- GHS-format safety data sheet
- Dangerous-goods declaration with UN number, class and packing group
- Commercial invoice, packing list and bill of lading or airway bill
- Certificate of origin and any destination-specific forms
Do you supply to my country?
Do you manufacture this yourself?
Request pricing on Para Nitrotoluene Ortho Sulphonic Acid
Send the form you need, your strength basis, iron and isomer limits, quantity, pack format and destination port. Our sourcing desk is available 24 hours a day, 7 days a week, and comes back with pricing per kilogram of active, lead time and packing options — whether that is a single trial drum or a contracted programme for the year.