Chlorosulfonic Acid
A fuming sulfonation and sulfation reagent, supplied as chlorosulfonic acid for dye intermediate, sulfonyl chloride and specialty chemical manufacture.
What is Chlorosulfonic Acid?
Chlorosulfonic Acid is a colourless to pale brown fuming liquid: a sulfuric acid molecule in which one hydroxyl has been replaced by chlorine. That single substitution is what gives it its reactivity, and its danger.
As a sulfonating agent it does what oleum does, but it can go a step further. Used in excess it carries the reaction through to the sulfonyl chloride, which is the gateway to sulfonamides and to reactive dye chemistry. It also avoids the large volume of spent sulfuric acid that an oleum sulfonation leaves behind, though it liberates hydrogen chloride that has to be scrubbed instead.
At Chelora Dyes, CSA is supplied to a controlled assay with free sulfuric acid, dissolved HCl and iron held low, in lined drums or by dedicated tanker for plants with dry receiving facilities.
- Appearance
- Fuming clear liquid
- Odour
- Sharp, choking
- Reactivity
- Violent with water
- Function
- Sulfonation
- Grade
- Technical
A chlorinated derivative of sulfuric acid
- Molecular formulaClSO3H
- Molecular weight116.52 g/mol
- IUPAC nameChlorosulfonic acid
- Functional groupsSulfonyl chloride, hydroxyl
- CAS number7790-94-5
Technical product information
Standard specification for Chelora Dyes' technical grade Chlorosulfonic Acid. Higher assay and low-colour grades are available on request.
| Chemical name | Chlorosulfonic Acid |
|---|---|
| Synonyms | Chlorosulphonic acid, CSA, Sulfuric chlorohydrin |
| CAS number | 7790-94-5 |
| Molecular formula | ClSO3H |
| Molecular weight | 116.52 g/mol |
| Assay (purity) | ≥ 98.0% |
| Appearance | Colourless to pale brown fuming liquid |
| Melting point | Approx. −80°C |
| Boiling point | 151–158°C (decomposes) |
| Density | Approx. 1.75 g/cm³ at 20°C |
| Free sulfuric acid | ≤ 1.5% |
| Dissolved HCl | ≤ 0.5% |
| Iron (as Fe) | ≤ 50 ppm |
| Water reactivity | Reacts violently; evolves HCl and heat |
| Transport classification | UN 1754, chlorosulfonic acid (verify against current documentation) |
| Packaging | 250 kg lined steel drums; ISO tanks and road tankers for bulk |
| Shelf life | 12 months in sealed, dry storage |
Applications of Chlorosulfonic Acid
Sulfonation of intermediates
Introduces sulfonic acid groups onto aromatic dye and pigment intermediates.
Sulfonyl chlorides
Carries the reaction through to sulfonyl chlorides, the entry point to sulfonamide chemistry.
Reactive dye chemistry
Supports the sulfonyl-based reactive systems used for cellulosic dyeing.
Detergent sulfonation
Used in surfactant and detergent alkylate sulfonation where a chloride route is preferred.
Pharmaceutical intermediates
Applied in sulfonation and sulfation steps across active ingredient manufacture.
Ion-exchange resins
Used to sulfonate polymer backbones in ion-exchange and membrane production.
Why choose Chelora Dyes
Controlled assay
Free sulfuric acid, dissolved HCl and iron held low for clean, predictable reactions.
Full documentation
COA, SDS, and transport classification supplied with every shipment.
Compliant logistics
Dry, lined packaging and dangerous goods paperwork handled end to end.
Technical support
Charging, scrubbing, and materials of construction guidance from our team.
Storage and guidelines
- Store in sealed, dry, vented containers in a cool, well-ventilated store.
- Keep the entire system absolutely dry — moisture drives corrosion and hydrogen generation.
- Route vents to an efficient scrubber; the material fumes continuously in air.
- Segregate from water, alkalis, alcohols, organics and oxidisable materials.
- Use dry carbon steel, glass-lined steel or PTFE; confirm materials for your conditions.
- Bund the storage area and keep dry neutralising media, not water, on hand for spills.
Handling precautions
Chlorosulfonic Acid causes immediate, deep chemical burns to skin and eyes and destroys tissue on contact. It also chars organic material including clothing.
It hydrolyses violently with water, liberating a large amount of heat and hydrogen chloride gas; contact between water and a bulk quantity can be explosive. Never apply water to a spill or to contaminated equipment.
The material fumes continuously in air, producing corrosive hydrogen chloride and sulfuric acid mist that severely damages the respiratory tract. Handle only in closed systems vented to a scrubber, with gas detection where fume may accumulate.
Only trained operators with full acid-resistant personal protective equipment, including face shield, apron and gauntlets, should handle it. Ensure emergency showers and eyewash are immediately available, and refer to the current Safety Data Sheet before any operation.
Frequently asked questions
What is Chlorosulfonic Acid used for?
It is a sulfonation and sulfation reagent. In dye manufacture it introduces sulfonic acid groups onto aromatic intermediates and gives access to sulfonyl chlorides, which are the entry point to sulfonamides and reactive dye chemistry. It is also used in detergent, pharmaceutical, resin and specialty chemical production.
How does it differ from oleum as a sulfonating agent?
Oleum sulfonates and leaves the sulfonic acid in place. Chlorosulfonic acid can do the same, but used in excess it converts the product through to the sulfonyl chloride, which opens a different branch of chemistry. It also avoids the large volume of spent sulfuric acid an oleum sulfonation generates, at the cost of liberating hydrogen chloride that has to be scrubbed.
Why does it fume in air?
It reacts instantly with atmospheric moisture, producing hydrogen chloride and sulfuric acid mist. Any open surface will fume continuously, which is why the material is handled in closed, dry systems vented to a scrubber.
What happens on contact with water?
It hydrolyses violently, releasing a large amount of heat and hydrogen chloride gas. The reaction can be explosive if water contacts a bulk quantity. Water ingress is the single most serious hazard associated with this material and systems must be kept dry.
What materials of construction are suitable?
Dry chlorosulfonic acid is handled in carbon steel, but any moisture makes it aggressively corrosive to metals and generates hydrogen. Glass, glass-lined steel and PTFE are used where dryness cannot be guaranteed. Confirm materials against your own conditions before commissioning.
What purity do you supply?
Standard grade is supplied at a minimum assay of 98%, with free sulfuric acid, dissolved hydrogen chloride and iron held within tight limits. Higher assay and low-colour grades can be supplied to order.
What packaging is available?
250 kg lined steel drums, and ISO tanks or road tankers for bulk supply. Bulk delivery requires suitable dry receiving facilities, which we will review before first shipment.
Is it hazardous to handle?
Yes, severely. It causes immediate and deep chemical burns, reacts violently with water, and continuously evolves corrosive hydrogen chloride and acid mist. It must be handled in closed, dry systems by trained operators with full acid protection, and the current Safety Data Sheet must be reviewed before any operation.
