Chlorosulfonic Acid
Chlorosulfonic acid is sulfuric acid with one hydroxyl swapped for chlorine — and that single substitution changes everything. It sulfonates and chlorinates at the same carbon in one pass, installing a sulfonyl chloride group that plain oleum simply cannot reach.
Chelora Chemicals supplies chlorosulfonic acid to dye, pharmaceutical, saccharin and detergent-intermediate 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
- 7790-94-5
- IUPAC name
- Sulfurochloridic acid
- Molecular formula
- ClHO₃S
- Molecular weight
- 116.52 g/mol
- EC / EINECS
- 232-234-6
- UN Number
- 1754 · Class 8
- SMILES
- OS(=O)(=O)Cl
- HS Code
- 2807 00*
* Confirm the exact HS heading with your customs broker — chlorosulfonic acid sits under the same chapter as sulfuric acid in most schedules but some destinations list it under a chlorinated-acid subheading.
What Chlorosulfonic Acid is used for
Chlorosulfonic acid is a colorless to pale yellow, fuming liquid that reacts violently with water, releasing hydrochloric and sulfuric acid mist. That same reactivity is what makes it valuable: it is the standard reagent for converting an aromatic ring directly into a sulfonyl chloride — sulfonation and chlorination in a single step.
Its largest commercial use is in saccharin manufacture, where it chlorosulfonates toluene en route to the sweetener. It is equally central to sulfonyl chloride and sulfa-drug chemistry, to dye-intermediate production where a sulfonamide group must be built onto a ring, and to ion-exchange-resin and detergent-intermediate synthesis.
Where it sits in the sulfuric-acid family
- Chlorosulfonic acid (this product) sulfonates and chlorinates in one step; the reagent of choice when a sulfonyl chloride is the target, not just a sulfonic acid.
- Oleum 65% sulfonates without introducing chlorine — the right choice when only a sulfonic acid or sulfate ester is needed. See that page.
- Thionyl chloride a common alternative route to sulfonyl chlorides from sulfonic acids already in hand, rather than directly from the aromatic ring.
- Sulfuryl chloride delivers chlorine without the sulfonic-acid step — a different reagent for a different synthetic target.
On this reagent the CAS number and grade matter more than the common name — state both on your purchase order. See the full acid and sulfonating-agent range.
Appearance and handling character
The material ships as a colorless to pale yellow, mobile, fuming liquid, fully miscible with and violently reactive toward water — contact releases hydrogen chloride gas and sulfuric acid mist simultaneously. Like oleum it must never have water added to it; it is added, slowly and with cooling, into water or the reaction medium. The safety section below should be read before any handling is planned.
| Parameter | Typical value |
|---|---|
| Appearance | Colorless to pale yellow fuming liquid |
| Assay (ClSO3H) | 98.0% min |
| Free SO₃ | Reported per batch |
| Free HCl / H2SO4 | Reported per batch |
| Color | Clear to pale yellow |
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. Assay and color are the figures that most affect downstream sulfonyl-chloride yield — tell us your target and we will quote against it.
| Property | Value |
|---|---|
| Physical state | Mobile liquid at ambient |
| Melting point | ≈ −80 °C |
| Boiling point | ≈ 151–155 °C, decomposes |
| Density | ≈ 1.753 g/cm³ @ 20 °C |
| Water reactivity | Violent — releases HCl and H2SO4/SO3 |
| Organic solubility | Miscible with chlorinated solvents |
Physical constants compiled from public reference data for CAS 7790-94-5 and rounded for readability. Treat them as orientation, not as a specification.
Where our customers put this reagent to work
This is a dual-function reagent. The interest lies in the sulfonyl chloride group it installs, not just the sulfonation step alone.
Saccharin manufacture
Chlorosulfonation of toluene is the first step of the classical route to saccharin, the single largest commercial use of this reagent.
- Toluene chlorosulfonation step
- Large-volume, scheduled consumption
- See our acid range
Sulfonyl chloride & sulfa-drug chemistry
Direct chlorosulfonation of aromatic rings builds sulfonamide-ready intermediates for sulfa antibiotics and related pharmaceutical actives.
- Pharmaceutical intermediate routes
- Sulfonamide precursor chemistry
- Technical desk review of your route
Dye intermediate sulfonation
Where a dye or pigment intermediate needs a sulfonamide rather than a plain sulfonic-acid group, chlorosulfonic acid is the direct route.
- Dye and pigment intermediates
- Colour-critical specification on request
- See our dye intermediate range
Detergent & surfactant intermediates
Selected anionic-surfactant and ion-exchange-resin routes use the reagent's dual reactivity to build sulfonate functionality efficiently.
- Surfactant precursor chemistry
- Ion-exchange resin production
- End-use declaration required
Agrochemical synthesis
Several agrochemical actives carry a sulfonyl or sulfonamide group introduced at this step of their synthesis.
- Custom synthesis quantities available
- Full impurity profile on request
- Technical support for your route
Contract & scheduled supply
Saccharin and pharma 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 Chlorosulfonic Acid
Chelora Chemicals is a supplier and sourcing partner, not a manufacturer. On a reagent whose commercial value is entirely in how cleanly it chlorosulfonates, owning no plant means we can route your order to the producer whose assay and color actually matches your reaction's tolerance.
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. 98% min is the commercial standard — we state the exact figure on the COA rather than a generic description.
- Color and free-acid content reported. Both signal hydrolysis or contamination, so they appear as their own COA lines.
- Batch COA shared before dispatch. You approve assay, color and free-acid content against your own spec while the material is still in our warehouse.
- Water reactivity stated up front. Violently reactive with water and corrosive by all routes — we say so at enquiry stage so your EHS team can plan the right controls.
- 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 1754 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 corrosive 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 the grade 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 production calendar instead of landing it all at once.
Water reactivity is the controlling hazard
Chlorosulfonic acid is severely corrosive to skin, eyes and the respiratory tract, and reacts violently with water, releasing hydrogen chloride gas and sulfuric acid mist simultaneously. 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.H335May cause respiratory irritation.EUH014Reacts violently with water.EUH029Contact with water liberates toxic gas.H290May be corrosive to metals.
Hazard statements reflect classifications commonly published for CAS 7790-94-5. The hydrogen chloride and sulfuric-acid mist released on water contact is itself a serious respiratory hazard, independent of liquid contact. 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 to the acid. The reagent is added, slowly and with cooling, into water or the reaction medium — reversing this order releases gas violently.
- Contain with dry inert absorbent. Dry sand or dry lime, never a combustible organic absorbent, and neutralise cautiously before disposal.
- Evacuate for the HCl/SO3 plume. A spill releases both hydrogen chloride and sulfuric-acid mist — treat the area as an inhalation hazard, not just a liquid-contact one.
- Treat burns immediately. Flush affected skin or eyes with copious water for at least 15 minutes and seek medical attention.
- Reaction quenching is exothermic. Any quench step in your process needs calorimetry and properly sized cooling; this is not a step to improvise on the day.
Storage
- Dedicated acid-duty tankage only. Glass-lined, Hastelloy or acid-resistant lined steel — standard stainless is attacked over time by this reagent.
- Keep bone dry. Moisture ingress triggers gas release and internal pressure — vent through a drying trap, never leave a container open to atmosphere.
- Segregate from water, organics and bases. Contact with any of these is exothermic and releases corrosive gas.
- Bunded, access-controlled area. A severely corrosive liquid needs secondary containment and restricted access as standard practice.
- Re-assay after extended storage. Color darkening or rising free-acid content signals partial hydrolysis.
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 the gas plume. Acid-gas cartridge respirators or supplied air during any operation that can release HCl or SO3, per your exposure assessment.
- Never mix with organics directly. Direct contact with many organic solvents and alcohols is strongly exothermic and can be violent.
Transport
Chlorosulfonic acid moves as regulated cargo under UN 1754, 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 assay, color and free-acid content — 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 1754, 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.
One molecule, two reactive sites
Chlorosulfonic acid carries both an acidic S=O system and a reactive chlorine on the same sulfur atom — which is why it can sulfonate and chlorinate an aromatic ring in a single pass. The routes below are the general industrial pattern, not a process disclosure.
Start from sulfur trioxide and HCl
Chlorosulfonic acid is manufactured by reacting SO3 with hydrogen chloride, or by chlorinating sulfuric acid under controlled conditions.
Electrophilic attack on the ring
The reagent attacks an activated aromatic ring, installing a –SO2Cl (sulfonyl chloride) group directly.
Isolate the sulfonyl chloride
The chlorosulfonated intermediate is separated from the spent acid phase and purified.
Convert onward
The sulfonyl chloride reacts with amines to give sulfonamides (saccharin, sulfa drugs) or with other nucleophiles for dye and surfactant chemistry.
Why assay and color carry through the whole route
On a dual-function reagent, small changes in purity show up immediately downstream:
- Free sulfuric or hydrochloric acid dilutes the active reagent. Partial hydrolysis products reduce effective chlorosulfonating strength per kilogram charged.
- Color darkening signals contamination. Iron or organic pickup during handling shows as color before it shows as an assay drop.
- Moisture is the single biggest yield risk. Any water ingress starts hydrolysis back toward sulfuric and hydrochloric acid, lowering effective strength before the reagent ever reaches your reactor.
- Particle-free, clear liquid is expected. Turbidity usually indicates incipient decomposition or contamination.
That is why we quote against your written assay requirement rather than a generic "technical grade", and why the batch COA is shared for approval before dispatch rather than sent with the invoice.
| Material | Downstream / use |
|---|---|
| Chlorosulfonic acid CAS 7790-94-5 — this product | Saccharin, sulfonyl chloride, sulfa-drug chemistry |
| Oleum 65% CAS 8014-95-7 | LAB/LAS sulfonation, mixed-acid nitration |
| Nitrosylsulfuric acid CAS 7782-78-7 | Diazotization, dye manufacture |
| 98% Sulfuric acid CAS 7664-93-9 | General acid-plant feedstock |
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.
Manufacturing route and scale
Chlorosulfonic acid is made from SO3 and HCl under controlled conditions — plant scale and campaign length both affect unit cost more than for a commodity acid.
- Fewer qualified producers than for plain oleum
- Scheduling around saccharin-plant campaigns helps
- We will tell you when a smaller pack suits better
Feedstock sulfur and chlorine economics
The chain runs back through elemental sulfur and chlor-alkali chlorine, so both markets feed through to price.
- Chlorine cost moves with the chlor-alkali cycle
- Sulfur tracks the broader acid market
- We flag feedstock-driven moves in the quote
Freight and DG surcharges
Class 8 water-reactive 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 economics
Plants making this reagent alongside other chlorosulfonated products price it against the whole slate, not in isolation.
- Ask us what the sister market is doing
- Contracted call-off smooths the exposure
- We hold a second qualified source
Regulatory handling obligations
Water-reactive acid handling carries storage-tank and operator-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 lower-volume 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 |
|---|---|
| Saccharin manufacture | 98% min assay, low free-acid content |
| Sulfa-drug / pharma intermediate | Tight color and purity spec, full impurity profile |
| Dye intermediate sulfonation | Assay matched to your coupling step |
| Surfactant / ion-exchange resin | Standard commercial grade |
| 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 assay and color before anything else. On this reagent both numbers decide whether a lot performs as expected, and we settle them in the first reply.
- Be straight about the hazard profile. Water-reactive, severely corrosive, gas-releasing on contact with moisture — stated at enquiry stage so your EHS team can plan.
- Review your receiving infrastructure. We ask about tank and hose materials before the first load moves, not after a compatibility failure.
- Review your specification before it goes into a contract. So you are not locked into a purity no plant can consistently hit.
Regulatory & compliance notes
- Water-reactive acid handling is jurisdiction-specific. Several regimes impose storage and 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 7790-94-5, 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 1754 classification filed, DG freight booked, export documents issued, and the consignment tracked through transit and clearance to your plant.
What buyers ask us about Chlorosulfonic Acid
What is chlorosulfonic acid used for?
How is it different from oleum?
Is it reactive with water?
What purity do you normally supply?
What is the minimum order quantity?
How long does delivery take?
How should we store it?
Is this a dangerous good? What paperwork comes with it?
Do you manufacture this yourself?
Request pricing on Chlorosulfonic Acid
Send your required 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.