Chlorosulfonic Acid
A high-purity sulfonating and chlorosulfonating agent supplied for dye, detergent, pharmaceutical, and specialty chemical manufacture.
What is Chlorosulfonic Acid?
Chlorosulfonic Acid — CSA — is a colourless to pale brown fuming liquid with a sharply pungent odour. Structurally it is sulfuric acid with one hydroxyl replaced by chlorine, which makes it the mono-acid chloride of sulfuric acid.
That single substitution changes everything about how it behaves. Where sulfuric acid sulfonates slowly and reversibly, CSA reacts fast and essentially irreversibly, introducing sulfonic acid or sulfonyl chloride groups onto an aromatic ring at moderate temperature.
At Chelora Chemicals, CSA is supplied to a controlled assay with free sulfuric acid and iron held to specification. It is one of the most hazardous products in this range: it reacts violently with water and must be handled only in dedicated, dry, closed systems by trained personnel.
- Appearance
- Colourless to pale brown fuming liquid
- Odour
- Sharply pungent, irritating
- Solubility
- Reacts violently with water
- Function
- Sulfonating / chlorosulfonating agent
- Grade
- Technical
Formula diagram
Sulfuric acid with one hydroxyl replaced by chlorine
- Molecular formulaHSO3Cl
- Molecular weight116.52 g/mol
- IUPAC nameChlorosulfonic acid
- Functional groupsSulfonyl chloride, acid
- CAS number7790-94-5
Technical product information
Standard specification for Chelora Chemicals' technical grade Chlorosulfonic Acid. Custom-grade and bulk specifications are available on request.
| Chemical name | Chlorosulfonic Acid |
|---|---|
| Synonyms | CSA, Chlorosulphonic acid, Sulfuric chlorohydrin |
| CAS number | 7790-94-5 |
| Molecular formula | HSO3Cl |
| Molecular weight | 116.52 g/mol |
| Assay (HSO3Cl) | ≥ 99.0% |
| Appearance | Colourless to pale brown fuming liquid |
| Density (20°C) | 1.75–1.76 g/cm³ |
| Boiling point | 151–158°C (with decomposition) |
| Melting point | −80°C |
| Free sulfuric acid | ≤ 1.0% |
| Iron (Fe) | ≤ 50 ppm |
| Packaging | 250 kg drums, IBC, dedicated road tanker |
| Shelf life | 12 months in sealed, dry original packaging |
Applications of Chlorosulfonic Acid
Dye intermediates
Sulfonates aromatic intermediates to give the water-soluble sulfonic acid groups that dye chemistry depends on.
Detergents & surfactants
Sulfonates alkylbenzenes and fatty alcohols in anionic surfactant manufacture.
Pharmaceutical synthesis
Introduces sulfonyl chloride groups en route to sulfonamides and related API structures.
Ion exchange resins
Sulfonates polymer backbones to create strongly acidic cation exchange materials.
Saccharin & specialty chemicals
Applied in the manufacture of sweeteners, brighteners, and specialty sulfonated products.
Pigment intermediates
Used in sulfonation steps within organic pigment and lake manufacture.
Why choose Chelora Chemicals
Every batch of Chlorosulfonic 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 ≥99% with free sulfuric acid and iron verified before dispatch.
Full documentation
COA, SDS, and regulatory data supplied with every shipment.
Flexible volumes
From 250 kg drums to IBC and dedicated road tanker supply.
Technical support
Process, handling, and compliance guidance from our chemistry team.
Storage and guidelines
- 01Store in dedicated, dry, tightly sealed containers in a cool, well-ventilated, bunded store.
- 02Exclude moisture absolutely — the product reacts violently with water and with humid air.
- 03Fit vessels with drying tubes or a dry inert gas blanket to prevent atmospheric moisture ingress.
- 04Segregate rigorously from water, alkalis, alcohols, amines, organic matter, and oxidising agents.
- 05Use appropriate materials: glass, glass-lined steel, or PTFE; carbon steel is used dry but corrodes rapidly if moisture is present.
- 06Keep containers in a locked, bunded area with clear signage and no water lines or sprinklers directly overhead.
Handling precautions
Chlorosulfonic acid causes severe skin burns and eye damage and is harmful or fatal if inhaled. It is for industrial use by trained personnel only, in closed systems.
It reacts violently and explosively with water, releasing hydrogen chloride and sulfuric acid mist and generating a large amount of heat. Never add water to the product, and never use a water jet on a spill or a fire involving it.
Because of that water reaction, standard water-based fire response is dangerous here. Fire and spill procedures must be written specifically for this product and rehearsed before the first delivery arrives, and emergency services should be told it is on site.
Contact with metals liberates hydrogen, which is flammable and can accumulate in a sealed vessel headspace.
Full acid suit, face shield, chemical goggles, and appropriate respiratory protection are required for any transfer. Emergency showers and eyewash must be functional and immediately accessible.
Spill response uses dry inert absorbent or dry soda ash, never water. Refer to the full Safety Data Sheet for neutralisation, disposal, and first-aid measures before use.
Frequently asked questions
What is Chlorosulfonic Acid used for?
It is a sulfonating and chlorosulfonating agent, used to introduce sulfonic acid or sulfonyl chloride groups in dye, detergent, pharmaceutical, ion exchange resin, and specialty chemical manufacture.
How does it differ from sulfuric acid as a sulfonating agent?
CSA reacts far faster and essentially irreversibly, and it can deliver a sulfonyl chloride rather than a sulfonic acid. Sulfuric acid sulfonation is slower, reversible, and produces water that has to be removed. The trade-off is that CSA is considerably more hazardous.
Why does it react so violently with water?
The sulfur–chlorine bond hydrolyses extremely rapidly, producing hydrogen chloride and sulfuric acid and releasing a great deal of heat almost instantly. Even atmospheric humidity causes the product to fume.
Can water be used on a spill or fire?
No. Water makes the situation dramatically worse by driving the violent hydrolysis reaction. Spill response uses dry inert absorbent or dry soda ash, and fire response uses dry chemical or carbon dioxide. This must be written into your site emergency plan and communicated to local emergency services.
What materials of construction are suitable?
Glass, glass-lined steel, and PTFE in normal service. Dry carbon steel is used industrially but corrodes rapidly once any moisture is present, so moisture exclusion is a materials issue as well as a safety one.
Why is free sulfuric acid specified?
It indicates partial hydrolysis from moisture ingress. Rising free acid means the product has been exposed to water, which reduces sulfonating power and signals a packaging or handling problem.
Why is iron content controlled?
Iron picked up from equipment discolours the product and can catalyse side reactions in sensitive sulfonation chemistry, particularly in dye manufacture where colour matters.
What PPE is required?
Full acid suit, face shield over chemical goggles, acid-resistant gloves and boots, and appropriate respiratory protection for any transfer operation. Emergency showers and eyewash must be immediately accessible and tested.
What packaging is available?
250 kg drums, IBCs, and dedicated road tankers. Supply requires confirmation of the receiving site's containment, dry handling capability, and emergency arrangements.
Is chlorosulfonic acid regulated?
It carries strict transport classification and workplace controls in most jurisdictions, and some markets impose additional site security or reporting requirements on highly reactive corrosives. Confirm your national obligations before ordering.
How should it be stored to preserve quality?
Dry, sealed, cool, and bunded, with drying tubes or a dry inert blanket on vessels. Moisture ingress is the single factor that degrades both the product and the safety of the installation.
Do you provide a Certificate of Analysis?
Yes. Every consignment ships with a Certificate of Analysis and Safety Data Sheet covering assay, free sulfuric acid, iron, density, and appearance, together with the required transport documentation.