Nitrosyl Sulfuric Acid NOHSO₄ · Nitrosylsulfuric Acid · CAS 7782-78-7
Chelora Chemicals is a supplier of Nitrosyl Sulfuric Acid, the mixed anhydride of sulfuric and nitrous acid used as a diazotising and nitrosating agent across azo dye and pigment manufacture, wherever a strongly acidic, non-aqueous diazotisation medium is required. Every consignment leaves with a batch-specific COA and the current SDS.
Also known as: Nitrosylsulfuric acid, Nitrosulphuric acid, NOHSO₄, Nitrating acid chamber crystals
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Price, lead time and a sample COA for Nitrosyl Sulfuric Acid, usually within one working day. We ship worldwide.
Request a Quote Email the DeskDocumentation
- Batch-specific COA (active content, free acid, specific gravity)
- Safety Data Sheet (SDS)
- UN 2308 dangerous-goods transport documents
- Third-party inspection on request
- Certificate of origin
What is Nitrosyl Sulfuric Acid?
Nitrosyl Sulfuric Acid is the mixed anhydride of sulfuric acid and nitrous acid, formula NOHSO₄ (also written HNO₅S). In its pure form it is a white to pale yellow crystalline solid that decomposes rather than melts on heating; for industrial supply and use it is almost always handled as a straw-coloured to yellow oily liquid — a solution in concentrated sulfuric acid.
Its value is as a nitrosonium (NO⁺) transfer reagent: it diazotises aromatic amines and carries out nitrosation, oxidation and oximation reactions under strongly acidic, low-water conditions — exactly the medium needed for diazotising weakly basic or poorly water-soluble amines used in azo dye and pigment synthesis.
Commercially it is produced either by absorbing nitrogen oxides into concentrated sulfuric acid or oleum, or by reacting sodium nitrite with cold concentrated sulfuric acid; on the dyestuff plant floor it is often generated in situ, immediately ahead of the diazotisation step.
Handling follows the precautions for a strong, corrosive, oxidising acid — acid-resistant gloves, face shield and eye protection, adequate ventilation or fume extraction given the nitrogen oxide fumes it can release, and storage away from organic materials and reducing agents.
Why Nitrosyl Sulfuric Acid specifically
- A non-aqueous diazotisation medium. Lets amines that are poorly soluble in water, or too weakly basic for the standard sodium nitrite/hydrochloric acid route, be diazotised cleanly in concentrated sulfuric acid.
- A single reagent in place of two. Replaces generating nitrous acid in situ from sodium nitrite and a mineral acid, simplifying the diazotisation step for disperse and other difficult-to-diazotise dye intermediates.
- Nitrosating and oxidising reagent. Used beyond diazotisation for nitrosation, oxidation and oximation chemistry, including in caprolactam-related nitrosation routes.
- Supplied ready to use. Available as a standardised solution so your diazotisation step does not depend on an in-house nitrosylsulfuric acid generation step.
How Nitrosyl Sulfuric Acid is Manufactured
Nitrosyl Sulfuric Acid is produced by combining a nitrogen oxide source with concentrated sulfuric acid.
- Nitrogen oxide absorption or nitrite addition. Nitrogen oxides (from nitric acid and sulfur dioxide, or from oxidised ammonia) are absorbed into cold concentrated sulfuric acid or oleum, or sodium nitrite is added directly to cold concentrated sulfuric acid.
- Temperature control. The reaction is run cold, since nitrosylsulfuric acid decomposes with loss of nitrogen oxides on warming.
- Standardisation. The resulting solution is standardised to the target active (nitrosyl) content, typically supplied as a solution in concentrated sulfuric acid.
- Quality release and packing. Active content, specific gravity and free-acid figures are confirmed against specification before the batch is packed and released.
Typical Commercial Specification
Figures below are representative of a commercial-grade nitrosylsulfuric acid solution. Tell us your downstream route and the concentration you need, and we will advise on the specification to order against.
| Parameter | Typical Value |
|---|---|
| Appearance | Straw-coloured to yellow oily liquid |
| Active (nitrosylsulfuric acid) content | Commonly supplied around 40% in concentrated sulfuric acid, to grade |
| Specific gravity | About 1.6 – 1.9, grade dependent |
| Colour | To grade; indicator of freshness ahead of use |
Physical & Chemical Properties
| Property | Value |
|---|---|
| Chemical formula | NOHSO₄ |
| Molecular weight | 127.08 g/mol (100% basis) |
| Appearance (solution) | Straw-coloured to yellow oily liquid |
| Appearance (pure solid) | White to pale yellow crystals; decomposes rather than melts above about 70 °C |
| Freezing point (40% solution) | About -10 °C |
| Boiling point | Decomposes, releasing nitrogen oxides, rather than boiling |
| Density (solution) | About 1.6 – 1.9 g/mL, grade dependent |
| Water solubility | Reacts (hydrolyses) with water |
| Incompatibilities | Water, organic materials, reducing agents |
Behaviour in the process
Nitrosyl sulfuric acid's reactivity is what dyestuff manufacturers are buying:
- Hydrolysis. Reacts with water to regenerate sulfuric acid and nitrous acid, the latter decomposing to release nitric oxide — this is both the basis of its reactivity and the reason it must be kept away from water in storage.
- NO⁺ transfer. Delivers the nitrosonium ion to aromatic amines for diazotisation, and to other substrates for nitrosation and oximation chemistry.
- Thermal sensitivity. Decomposes on warming rather than boiling; the reaction and storage temperature both need to be controlled.
Nitrosyl Sulfuric Acid and Related Diazotising Routes
Choosing between diazotising systems comes down to the amine's solubility and basicity, and the acidity the downstream coupling step needs.
| System | Medium | When it is the right choice |
|---|---|---|
| Nitrosyl Sulfuric Acid | Concentrated sulfuric acid | Weakly basic or poorly water-soluble amines, and non-aqueous diazotisation |
| Sodium nitrite + HCl | Aqueous, dilute acid | Standard, more basic, water-soluble amines |
| Sodium nitrite + H₂SO₄ (in situ) | Sulfuric acid, generated on site | Smaller-scale or occasional diazotisation where an off-the-shelf reagent is not justified |
| Isoamyl nitrite / alkyl nitrites | Organic solvent | Non-aqueous diazotisation in organic media, typically lab/pilot scale |
Stated plainly: nitrosyl sulfuric acid earns its place wherever the amine will not diazotise cleanly in the standard aqueous system — it is not a universal replacement, but the reagent of choice for that difficult class of substrates.
Industries We Supply Nitrosyl Sulfuric Acid To
The same reagent feeds a dye-manufacturing diazotisation line and a fine-chemical producer running nitrosation or oximation chemistry. What changes is the scale and the documentation each requires.
Where Nitrosyl Sulfuric Acid is Used
In the diazotisation step
The amine is dissolved or suspended in the acidic medium and nitrosyl sulfuric acid is added under temperature control to generate the diazonium salt in situ, which is then coupled to build the target azo dye or pigment. Running the step in concentrated sulfuric acid, rather than the standard aqueous system, is often exactly why this reagent is specified for a given amine.
Need a specific concentration?
Tell us the active content your diazotisation process runs on, the packing format you can receive and the annual quantity. We will come back with a price, a lead time and a sample COA.
Quality Control & Testing
Every lot is released against a batch-specific Certificate of Analysis, with active (nitrosyl) content and specific gravity reported because both determine how much reagent your diazotisation step needs.
- Active content — by titration, the primary grade measure and the figure your dosing is based on.
- Specific gravity — reported because it is the quickest in-plant check that a delivered drum matches its COA.
- Colour — reported as a freshness indicator; nitrosylsulfuric acid solutions darken as they age or warm.
Common Process Problems & Likely Causes
| Symptom | Likely cause | What to check |
|---|---|---|
| Incomplete diazotisation | Active content lower than expected, or reagent aged in storage | Active content and age of the lot on the COA |
| Excess fuming / NOx evolution on dosing | Reagent warmed in transit or storage | Storage temperature history; specific gravity on receipt |
| Off-colour or low-yield diazonium salt | Reagent contacted moisture, partially hydrolysing it | Container seal integrity and storage conditions |
Packaging, Storage & Shipping
- Standard packing. Acid-resistant drums or ISO tanks, matched to the corrosive, moisture-sensitive nature of the product.
- Moisture exclusion. Keep containers tightly sealed at all times — contact with water or atmospheric moisture hydrolyses the product and releases nitrogen oxide fumes.
- Temperature control. Store cool; warming accelerates decomposition and nitrogen oxide release.
- Material compatibility. Avoid contact with organic materials and reducing agents given the product's strong oxidising character.
- Transport classification. Commonly shipped under UN 2308, Class 8, Packing Group II — confirm the correct entry against your own current SDS before shipping.
Hazards & Safe Handling
Nitrosyl Sulfuric Acid is corrosive, causing severe skin burns and eye damage, and is toxic if swallowed, in contact with skin or if inhaled. It is also an oxidiser. Standard precautions for a strong, fuming mineral acid and good plant practice apply throughout handling. Refer to the current SDS for your grade for the complete hazard classification.
- Skin and eye contact. Acid-resistant gloves, face shield and full eye protection are mandatory; rinse immediately and thoroughly with water on contact and seek medical attention.
- Inhalation. Nitrogen oxide fumes are released on contact with moisture or on warming; use adequate ventilation or local exhaust and avoid breathing fumes.
- PPE. Acid-resistant gloves and apron, face shield or chemical splash goggles, and respiratory protection where fume exposure is possible.
- Environment. Corrosive and reactive with water; never discharge to drains or water courses, and follow local effluent and spill-response rules.
Regulatory & Compliance Notes
Nitrosyl Sulfuric Acid is a long-established industrial reagent. Because obligations differ by territory and use, the notes below are orientation rather than legal advice.
- GHS classification. Commonly classified as corrosive to skin and eyes (Category 1), toxic by the oral, dermal and inhalation routes, and as an oxidising liquid; the SDS carries the full hazard statements for your grade.
- REACH and chemical inventories. Registered under EU REACH and listed on major chemical inventories.
- Dangerous goods transport. Commonly shipped under UN 2308 (Nitrosylsulphuric acid, liquid), Class 8, Packing Group II. Confirm the correct entry with your logistics/EHS team against your current SDS before shipping.
- HS code. Commonly declared alongside nitric/sulphonitric acid preparations; confirm the exact tariff line with your customs broker for your jurisdiction.
We Supply Nitrosyl Sulfuric Acid Worldwide
Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Nitrosyl Sulfuric Acid from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation and freight so the material arrives ready to use.
- Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
- Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other ports arranged as routing allows.
- Documentation. Commercial invoice, packing list, certificate of origin, COA and SDS issued as a complete set.
- Flexible volumes. From drum quantities up to ISO-tank bulk shipments on a supply contract.
Buying Nitrosyl Sulfuric Acid from Chelora
We are an independent sourcing and supply partner. For this product that means settling three things at enquiry: the active-content grade your diazotisation process runs on, the packing format, and the quantity you are buying.
- Documentation on every lot. Batch-specific COA with active content and specific gravity, plus the current SDS.
- Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can confirm the active content.
- Quantities. Drum quantities through to larger ISO-tank shipments on contract supply.
- Inspection. Independent third-party inspection available at loading when the contract requires it.
- Related dye-process chemicals. Para Chloro Ortho Nitro Aniline, meta-Nitrotoluene and other dye and pigment intermediates alongside this product from one supplier.
How ordering works
- Send the enquiry. Active-content grade, quantity, destination port and the Incoterm you buy on.
- We quote. Price, lead time, packing format and a sample COA, normally within one working day.
- Qualify the supply. For first orders, we share the analysis so your technical team can confirm active content before you commit.
- Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
- Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.
Nitrosyl Sulfuric Acid — Common Questions
The questions our technical desk is asked most often about Nitrosyl Sulfuric Acid. If yours isn't here, call or email and you will reach someone who knows the chemistry.
What is the CAS number of Nitrosyl Sulfuric Acid?
The CAS number for Nitrosyl Sulfuric Acid is 7782-78-7, and its EC number is 231-964-2. Its formula is NOHSO₄ with a molecular weight of 127.08 g/mol on a 100% basis.
What is Nitrosyl Sulfuric Acid used for?
It is used mainly as a diazotising agent for amines that do not diazotise cleanly in the standard aqueous sodium nitrite system, and more broadly as a nitrosating, oxidising and oximating reagent in fine-chemical synthesis.
Do you supply Nitrosyl Sulfuric Acid worldwide?
Yes. Chelora Chemicals supplies and exports Nitrosyl Sulfuric Acid worldwide — across Asia Pacific, Europe, the Middle East, Africa and the Americas, as well as throughout India. Every consignment carries the COA and SDS.
How is it different from the standard sodium nitrite diazotisation?
Standard diazotisation generates nitrous acid in situ from sodium nitrite and a mineral acid in water. Nitrosyl sulfuric acid delivers the same nitrosonium chemistry directly, in a concentrated sulfuric acid medium, which suits amines that are poorly soluble in water or too weakly basic for the aqueous route.
How is Nitrosyl Sulfuric Acid manufactured?
By absorbing nitrogen oxides into cold concentrated sulfuric acid or oleum, or by reacting sodium nitrite with cold concentrated sulfuric acid, then standardising the resulting solution to the target active content.
Is Nitrosyl Sulfuric Acid hazardous?
It is corrosive, causing severe skin burns and eye damage, toxic if swallowed, in contact with skin or if inhaled, and an oxidiser. Refer to the current SDS for your grade for the complete hazard classification.
What is the UN number and transport classification?
Nitrosylsulfuric acid, liquid, is commonly shipped under UN 2308, Class 8 (corrosive), Packing Group II. Confirm against your own current SDS before relying on it for shipping documentation.
What concentration is it supplied at?
It is commonly supplied as a solution around 40% active content in concentrated sulfuric acid, though exact concentration varies by grade — tell us what your process runs on and we will match it.
How should Nitrosyl Sulfuric Acid be stored?
In tightly sealed, acid-resistant containers, kept cool and strictly away from water, moisture and organic materials, since contact with water hydrolyses the product and releases nitrogen oxide fumes.
Can Nitrosyl Sulfuric Acid be mixed with water?
No — it reacts with water, regenerating sulfuric and nitrous acid and releasing nitrogen oxide fumes. Any dilution or quenching step should follow the procedure in the current SDS.
What packing sizes and order quantities are available?
Acid-resistant drums up to ISO-tank bulk formats, available on contract supply. Orders run from trial quantities up to repeat bulk loads.
Ready to source Nitrosyl Sulfuric Acid?
Send us the active-content grade your process runs on and your annual volume. You will get a price, a realistic lead time and a sample COA from someone who understands what the material has to do in your process — delivered anywhere in the world.