Nitrosylsulfuric Acid
Nitrosylsulfuric acid delivers a nitrosonium cation (NO⁺) in a strongly acidic medium — a diazotization reagent that comes pre-mixed with its own acid, replacing the sodium nitrite + sulfuric acid combination many dye plants use on smaller scale.
Chelora Chemicals supplies nitrosylsulfuric acid to dye, pigment and fine-chemical producers worldwide, in acid-duty drums and ISO tanks, with a batch COA and GHS safety data sheet on every consignment.
Product identity
- CAS Number
- 7782-78-7
- IUPAC name
- Nitrosylsulfuric acid
- Molecular formula
- NOHSO₄
- Molecular weight
- 127.08 g/mol
- EC / EINECS
- 231-964-2
- UN Number
- 2308 · Class 8
- SMILES
- O=NOS(=O)(=O)O
- HS Code
- 2808 00*
* Confirm the exact HS heading with your customs broker — mixed nitrogen/sulfur oxoacids can sit under different subheadings from plain nitric or sulfuric acid depending on the destination tariff schedule.
What Nitrosylsulfuric Acid is used for
Nitrosylsulfuric acid is the mixed anhydride of sulfuric acid and nitrous acid — a pale yellow crystalline solid when pure, almost always supplied and handled as a straw-colored to green, fuming liquid solution in sulfuric acid (commonly around 40% NOHSO₄). It carries the nitrosonium cation in a strongly acidic medium, ready to react.
Its main commercial use is as a diazotization reagent: dye and pigment manufacturers use it to convert an aromatic amine directly to a diazonium salt in one controlled addition, without the separate sodium-nitrite step that smaller batch processes rely on. It also has an established role as a nitrosating agent in caprolactam production, and historically was part of the lead-chamber process for sulfuric acid itself.
Where it sits relative to other diazotization routes
- Nitrosylsulfuric acid (this product) a one-reagent diazotization system; favoured on continuous or large-batch dye and pigment lines.
- Sodium nitrite + sulfuric acid the classical two-component diazotization route, generated in-situ at the point of use.
- Chlorosulfonic acid a different sulfur-based reagent entirely — used for sulfonyl chloride formation, not diazotization. See that page.
- Fast Bordeaux GP Base a typical azoic diazo component that nitrosylsulfuric acid (or NaNO2/H2SO4) is used to diazotize before coupling. See that page.
State the % NOHSO4 content and sulfuric-acid carrier strength on your purchase order — see the full acid and dye-intermediate range.
Appearance and handling character
The commercial material ships as a clear yellow to green, fuming, oily liquid in sulfuric acid solution, reacting vigorously with water to release gaseous nitrogen dioxide (NO2). It is a strong oxidizing agent as well as a corrosive acid, and both hazards need to be designed for together, not separately. The safety section below should be read before any handling is planned.
| Parameter | Typical value |
|---|---|
| Appearance | Clear yellow to green liquid |
| Assay (NOHSO4, titration) | 38 – 42% w/w |
| Free H2SO4 (carrier) | Reported per batch |
| Iron | Reported per batch |
| Color / clarity | May develop turbidity on standing |
Important: the figures above are indicative of commercial-grade solution and are offered for planning only. The batch certificate of analysis is the governing document. NOHSO4 assay is the figure that decides your diazotization stoichiometry — tell us your target concentration and we will quote against it.
| Property | Value |
|---|---|
| Physical state | Fuming liquid solution at ambient |
| Melting point (pure NOHSO4) | ≈ 70–73 °C, decomposes |
| Decomposition | Decomposes rather than boils |
| Density (40% solution) | ≈ 1.865 g/mL @ 20 °C |
| Water reactivity | Vigorous — releases gaseous NO2 |
| Oxidizing character | Strong oxidizer |
Physical constants compiled from public reference data for CAS 7782-78-7 and rounded for readability. Treat them as orientation, not as a specification.
Where our customers put this reagent to work
This is a single-function reagent with an outsized role: it is how an amine becomes a diazonium salt, the hinge step of almost every azo dye and pigment.
Dye diazotization
Converts aromatic amines to diazonium salts in a single controlled addition, the step immediately before coupling to give an azo dye or pigment.
- One-reagent diazotization system
- Favoured on continuous dye lines
- See our dye intermediate range
Azo pigment manufacture
The same diazotization chemistry underlies diarylide and azo pigment production, where consistent NOHSO4 strength controls batch-to-batch shade.
- Pigment-grade documentation available
- Colour-critical specification on request
- See our pigment intermediate range
Caprolactam nitrosation step
Industrially used as a nitrosating agent in one established route to caprolactam, the monomer for nylon-6.
- Fine-chemical / polymer feedstock use
- Custom concentration on request
- Technical desk review of your route
Fine chemical & agrochemical synthesis
Several nitrosation and diazotization steps in agrochemical and specialty-chemical routes draw on this reagent where in-situ nitrite generation is impractical at scale.
- End-use declaration required
- Custom synthesis quantities available
- Technical support for your route
Historical acid-plant role
Nitrosylsulfuric acid was an intermediate in the lead-chamber process for sulfuric acid — a role now mostly superseded by the contact process.
- Reference / specialty interest only
- Documentation on request
- Ask our technical desk
Contract & scheduled supply
Continuous dye and pigment plants consume this reagent on a fixed schedule. We hold inventory and release it against your production calendar.
- Annual contracts with scheduled call-off
- Price held across the contract period
- Second source held in reserve
How we supply Nitrosylsulfuric Acid
Chelora Chemicals is a supplier and sourcing partner, not a manufacturer. On a reagent where a MCA case history records an explosion from using too concentrated a batch against too reactive a substrate, owning no plant means we can route your order to the producer whose solution strength and packaging actually matches how you add it.
We place your order with whichever qualified producer best matches your assay, your specification, your price point and your delivery window.
We keep a second qualified source on this line. When a plant goes down for maintenance, your order switches source rather than stalling.
- Assay confirmed before we quote. 38–42% NOHSO4 is the commercial band — we state the exact figure on the COA rather than a generic description.
- Carrier-acid strength reported. The sulfuric-acid concentration it is dissolved in affects your reaction stoichiometry as much as the NOHSO4 content does.
- Batch COA shared before dispatch. You approve assay, iron and clarity against your own spec while the material is still in our warehouse.
- Oxidizer-plus-corrosive hazard stated up front. This reagent is both a strong oxidizer and a severely corrosive acid — we say so at enquiry stage so your EHS team plans for both.
- Pre-shipment samples for qualification. New account or new source, your laboratory runs a trial before the full quantity ever moves.
- Export machinery handled in-house. UN 2308 classification, approved packing, labelling, freight booking and customs paperwork are ours to manage.
Packed the way your plant receives it
Pack format drives your landed cost and your handling effort. Tell us how the material will be charged at your end and we will quote the format that suits your operation.
Lined steel drums
Acid-resistant lined drums for Class 8 oxidizing-acid liquids — the standard commercial format for this reagent.
ISO acid tank containers
Dedicated acid-duty ISO tanks for bulk movement, avoiding repeated decanting and its associated exposure risk.
Road tanker (regional)
Acid-duty tankers for domestic and cross-border delivery where receiving infrastructure exists at both ends.
Trial / sample quantities
Small, DG-compliant containers dispatched so your R&D team can qualify concentration before committing to larger volumes.
Incoterms to suit you
Quoted on the Incoterm your purchasing team works to, with DG documentation filed before the booking is made.
Campaign despatch
We hold contracted tonnage and release it against your dye or pigment plant's production calendar instead of landing it all at once.
Oxidizer plus corrosive — plan for both
Nitrosylsulfuric acid is a strong oxidizing agent as well as a severely corrosive, toxic acid, and reacts vigorously with water to release gaseous nitrogen dioxide. The summary below is orientation only — the safety data sheet supplied with your consignment is the authoritative document.
Classified hazards
H272May intensify fire; oxidizer.H314Causes severe skin burns and eye damage.H301 + H311Toxic if swallowed or in contact with skin.EUH014Reacts violently with water.EUH029Contact with water liberates toxic gas.
Hazard statements reflect classifications commonly published for CAS 7782-78-7. A documented MCA case history records a fatal explosion from diazotizing an over-concentrated nitroaniline substrate with this reagent — reaction scale-up on this chemistry needs careful calorimetric review. Always read the SDS issued with your specific batch.
Spill & emergency orientation
Plan your response before the pallet arrives. Sections 4, 5 and 6 of the SDS are the authoritative instructions and should be posted at the point of use.
- Never add water directly to the acid. Water contact releases gaseous NO2 rapidly — dilution, where required, is done slowly with cooling into a large excess of water, never the reverse.
- Contain with dry inert absorbent. Dry sand or dry lime, never a combustible organic absorbent, and neutralise cautiously before disposal.
- Evacuate for the NO2 plume. Nitrogen dioxide is a serious respiratory hazard that can cause delayed pulmonary effects — treat any spill as an inhalation emergency.
- Treat burns and exposure immediately. Flush affected skin or eyes with copious water and seek medical attention; anyone exposed to the gas plume should be assessed even if symptoms are delayed.
- Reaction addition order matters. Diazotization with this reagent is exothermic and substrate-concentration sensitive — follow validated addition rates and never scale up without calorimetry.
Storage
- Dedicated acid-duty tankage only. Glass-lined or acid-resistant lined steel, rated for both oxidizing and corrosive duty.
- Keep bone dry and cool. Moisture ingress releases NO2 gas and builds pressure; heat accelerates decomposition — vent through a drying trap.
- Segregate from reducing agents and organics. As a strong oxidizer, contact with combustibles or reducing agents can be violent.
- Bunded, access-controlled area. A severely corrosive, oxidizing liquid needs secondary containment and restricted access as standard practice.
- Re-assay before use after storage. NOHSO4 content can drift with temperature history — confirm strength before charging a new batch.
Handling & PPE
- Closed transfer only. Pump or gravity-feed through sealed, acid-rated lines; never open-pour or sample without local exhaust ventilation.
- Full acid-resistant PPE. Face shield over chemical goggles, acid suit, and gauntlet-length nitrile or butyl gloves for every connection and disconnection.
- Emergency deluge shower and eyewash on site. Within seconds' reach of every transfer point, tested and logged routinely.
- Respiratory protection for NO2. Acid-gas cartridge respirators or supplied air during any operation that can release nitrogen oxides, per your exposure assessment.
- Validate reaction scale before plant trial. Confirm substrate concentration and addition rate at bench scale before any increase in batch size on this chemistry.
Transport
Nitrosylsulfuric acid moves as regulated cargo under UN 2308, Class 8. We classify each consignment, confirm tanker or drum compatibility, apply UN-approved labelling and file the dangerous-goods declaration before the booking is made — 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 NOHSO4 assay, carrier-acid strength, iron and clarity — 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 and disposal, issued in the language your destination requires.
Dangerous Goods Declaration
UN 2308, hazard class and IMDG or RID/ADR declaration prepared and filed before the tanker or container is booked.
Certificate of Origin
Chamber-attested where required, plus preferential-origin forms where a trade agreement gives your import duty relief.
Third-party inspection
SGS, Intertek or Bureau Veritas sampling and inspection arranged on request before loading, giving you independent verification of what ships.
Retained & pre-shipment samples
Pre-shipment samples carry the same COA as the commercial lot, so what your laboratory qualifies is exactly what arrives.
A diazotization reagent that carries its own acid
The nitrosonium ion is the reactive core of this reagent — generated separately as nitrosylsulfuric acid, it reaches the amine already in an acidic medium, with no separate nitrite addition needed. The routes below are the general industrial pattern, not a process disclosure.
Generate from SO2, HNO3 and H2SO4
Sulfur dioxide and nitric acid react in concentrated sulfuric acid to form nitrosylsulfuric acid, or sodium nitrite is dissolved directly into sulfuric acid.
Dose onto the aromatic amine
The reagent is added under controlled temperature to the amine substrate dissolved in its own acid medium.
Form the diazonium salt
The nitrosonium ion reacts with the amine to give a diazonium salt, the reactive intermediate for coupling.
Couple to the dye or pigment
The diazonium salt couples immediately with a naphthol or amine coupling component to give the finished azo colourant.
Why assay and addition control carry through the whole route
On a reagent that both oxidizes and diazotizes, control of strength and rate is the entire process:
- NOHSO4 assay sets your stoichiometry directly. Under-strength material leaves unreacted amine in the batch; over-strength material risks runaway side reactions.
- Substrate concentration is a documented hazard. The historical MCA case on this reagent involved an over-concentrated substrate — dilution and addition rate matter as much as reagent purity.
- Iron and color signal carrier-acid quality. Contamination in the sulfuric-acid carrier can colour sensitive dye batches.
- Temperature control decides side-product formation. Diazotization above the validated temperature window reduces yield and generates tar.
That is why we quote against your written concentration requirement rather than a generic "nitrosylsulfuric acid" label, and why the batch COA is shared for approval before dispatch rather than sent with the invoice.
| Material | Downstream / use |
|---|---|
| Nitrosylsulfuric acid CAS 7782-78-7 — this product | Diazotization, caprolactam nitrosation |
| Oleum 65% CAS 8014-95-7 | LAB/LAS sulfonation, mixed-acid nitration |
| Chlorosulfonic acid CAS 7790-94-5 | Sulfonyl chloride & saccharin chemistry |
| Fast Bordeaux GP Base CAS 96-96-8 | Typical azoic diazo component diazotized with this reagent |
We supply across this intermediate family — see the full intermediate range. Send the CAS number and we will confirm the correct material before quoting.
What actually moves the price of this product
Knowing what drives the quote helps you time a purchase and read whether an offer is realistic.
NOHSO4 concentration sets the cost
Higher-assay solutions concentrate more reactive material per kilogram shipped, which affects both manufacturing cost and freight efficiency.
- 38–42% is the standard commercial band
- Custom concentrations quoted on request
- We flag when a standard grade would do
Feedstock nitric and sulfuric acid
The reagent is built from nitric acid, sulfur dioxide and sulfuric acid — all three feed through to price on their own cycles.
- Nitric-acid market moves feed through in weeks
- We note feedstock-driven swings in the quote
- Contracted call-off smooths exposure
Freight and DG surcharges
Class 8 oxidizing-corrosive cargo carries a hazardous surcharge, and tanker space for this reagent is thinner than for general acids.
- Compare on landed cost, not ex-works
- DG space books out ahead of peak season
- We quote FOB, CIF, CFR or DDP as you prefer
Co-product plant economics
Producers making this reagent alongside other nitrogen-oxide chemistry price it against the whole output slate.
- Ask us what the sister market is doing
- Contracted call-off smooths the exposure
- We hold a second qualified source
Regulatory handling obligations
Oxidizing-acid handling carries storage and training obligations in several jurisdictions, which sit inside the delivered price.
- Handling obligations vary by jurisdiction
- We check destination rules before quoting
- Ask about documentation for your site
Source availability
A plant turnaround or feedstock disruption can take capacity offline at short notice on this specialty reagent.
- We hold a second qualified source on this line
- Qualify the alternate before you need it
- Ask us about dual-source contracts
| If your end use is… | Specify |
|---|---|
| Dye / pigment diazotization | 38–42% NOHSO4, low iron, consistent carrier-acid strength |
| Caprolactam nitrosation | Concentration matched to your established process window |
| Fine-chemical synthesis | Full impurity profile, end-use declaration |
| Laboratory / trial | Small DG-compliant pack, full COA |
Not sure which column you are in? Describe what you make from it and our technical desk will recommend the 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
- Confirm NOHSO4 assay before anything else. On this reagent that figure decides your diazotization stoichiometry, and we settle it in the first reply.
- Ask about your substrate and scale. Given the documented hazard history on this chemistry, we flag substrate-concentration risk at enquiry stage rather than after an order ships.
- Be straight about the hazard profile. Oxidizer plus severely corrosive, gas-releasing on water contact — stated up front so your EHS team can plan for both.
- Review your specification before it goes into a contract. So you are not locked into a concentration no plant can consistently hit.
Regulatory & compliance notes
- Oxidizing-acid handling is jurisdiction-specific. Several regimes impose storage-tank and operator-training obligations for this class of reagent. Confirm what applies at your site before the first delivery.
- Import controls vary by destination. We check 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 neutralisation rules matter. Check your discharge consent against the material before introducing it to site.
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 7782-78-7, target NOHSO4 assay, quantity, pack preference and destination port.
Receive a firm quote
Pricing, 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
UN 2308 classification filed, DG 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 Nitrosylsulfuric Acid
What is nitrosylsulfuric acid used for?
How is it different from the classical sodium nitrite route?
Is it dangerous to scale up this chemistry?
What assay do you normally supply?
Is it reactive with water?
What is the minimum order quantity?
How should we store it?
Is this a dangerous good? What paperwork comes with it?
Do you manufacture this yourself?
Request pricing on Nitrosylsulfuric Acid
Send your required NOHSO4 assay, quantity, pack format and destination port. Our sourcing desk is available 24 hours a day, 7 days a week, and comes back with pricing, lead time and packing options — whether that is a single trial drum or a contracted programme for the year.