Substance profile
Chlorosulfonic acid
Chlorosulfonic acid is a colorless or slightly yellow liquid with a PUNGENT odor.
01 · Identification
What Chlorosulfonic acid is
Chlorosulfonic acid is a colorless or slightly yellow liquid with a PUNGENT odor. Its molecular formula is ClHO3S and its molecular weight is 116.53 g/mol. It boils at 155 °C, melts at -80 °C.
Under the GHS it carries the signal word Danger. It is classed as corrosives.
02 · Identifiers
Chlorosulfonic acid identifiers and molecular data
Chlorosulfonic acid CAS number and EC number
Chlorosulfonic acid molecular formula and molecular weight
Other names for Chlorosulfonic acid
- chlorosulphonic acid
03 · GHS classification
Chlorosulfonic acid hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Chlorosulfonic acid pictograms and signal word
Chlorosulfonic acid hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
| Specific target organ toxicity - single exposure GHS chapter 3.8 | Category 3 | H335 | GHS07 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Chlorosulfonic acid hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H335 | May cause respiratory irritation. |
| H314 | Causes severe skin burns and eye damage. |
Chlorosulfonic acid supplemental EU statements (EUH)
| Code | Statement |
|---|---|
| EUH014 | Reacts violently with water. |
This page lists only the codes assigned to Chlorosulfonic acid. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Chlorosulfonic acid
A Safety Data Sheet is written for a product, not for a substance: the supplier of the grade you actually buy issues it, so two suppliers of Chlorosulfonic acid issue two different sheets. That is why there is no single authoritative SDS for a substance to download — what there is, is the job of collecting the sheets for the products you hold and keeping them current as suppliers revise them.
04 · Precautionary statements
Chlorosulfonic acid precautionary statements
CLP Annex VI assigns 5 precautionary statements to Chlorosulfonic acid. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Chlorosulfonic acid name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | хлоросулфонова киселина |
| Spanish español | Ácido clorosulfónico |
| Czech čeština | chlorosírová kyselina |
| Danish dansk | chlorsulfonsyre |
| German Deutsch | Chlorschwefelsäure Chlorsulfonsäure |
| Estonian eesti | klorosulfoonhape |
| Greek ελληνικά | χλωροσουλφονικό οξύ |
| English English | chlorosulphonic acid |
| French français | acide chlorosulfonique |
| Croatian hrvatski | klorosulfonska kiselina |
| Italian italiano | acido clorosolfonico |
| Latvian latviešu | hlorsulfonskābe |
| Lithuanian lietuvių | chlorsulfonrūgštis |
| Hungarian magyar | klórszulfonsav |
| Maltese Malti | aċidu klorosulfoniku |
| Dutch Nederlands | chloorsulfonzuur |
| Polish polski | kwas chlorosiarkowy(VI) kwas chlorosulfonowy |
| Portuguese português | ácido clorossulfónico |
| Romanian română | acid clorosulfonic |
| Slovak slovenčina | kyselina chlórsírová |
| Slovenian slovenščina | klorožveplova kislina |
| Finnish suomi | kloorisulfonihappo |
| Swedish svenska | klorsulfonsyra |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Chlorosulfonic acid GHS label elements
Everything CLP Annex VI fixes for Chlorosulfonic acid, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Chlorosulfonic acid
- May cause respiratory irritation.
- Causes severe skin burns and eye damage.
- Reacts violently with water.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- Immediately call a POISON CENTER/doctor/…
- Do NOT induce vomiting.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Chlorosulfonic acid in the GHS label constructor →
07 · Health hazards
Chlorosulfonic acid health hazards and exposure limits
Chlorosulfonic acid hazard summary
Highly corrosive to skin; [Quick CPC] High inhalation exposure can induce pulmonary edema; [CHEMINFO] A corrosive substance that can cause pulmonary edema; May cause erosion of teeth enamel; [ICSC] Reacts with water to produce hydrochloric and sulfuric acid; [AIHA]
Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
08 · Physical and chemical properties
Chlorosulfonic acid properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Chlorosulfonic acid boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 155 °C (311 °F) | at 760 mmHg | CAMEO |
| 152 °C (305.6 °F) | at 760 mmHg | DOE PAC | |
| 151.5 °C (304.7 °F) | range, midpoint shown, at 755 mmHg | HSDB |
Chlorosulfonic acid melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -80 °C (-112 °F) | HSDB |
Chlorosulfonic acid density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 1.75 g/cm³ | ICSC | |
| 1.75 g/cm³ | at 20 °C | CAMEO | |
| 1.75 g/cm³ | at 25 °C | DOE PAC |
Chlorosulfonic acid solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | /COMMON SOLVENTS INCLUDE/ LIQUID SULFUR DIOXIDE, PYRIDINE, & DICHLOROETHANE. | HSDB | |
| Solubility in water: reaction | ICSC |
Chlorosulfonic acid vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 1.55 mmHg | CAMEO | |
| 0.9976 mmHg | at 20 °C | ICSC | |
| 1 mmHg | at 32 °C | HSDB |
Chlorosulfonic acid autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | Not flammable (USCG, 1999) | CAMEO |
Chlorosulfonic acid lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | ON DROPPING INTO WATER DECOMP WITH EXPLOSIVE VIOLENCE. | HSDB |
Chlorosulfonic acid vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 4.02 (air = 1) | HSDB |
Chlorosulfonic acid corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | CORROSIVE MATERIAL. | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Chlorosulfonic acid fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Chlorosulfonic acid fire potential
Not combustible, but if involved in a fire decomposes rapidly to produce hydrogen chloride, sulfur dioxide, sulfuric acid. Evolves hydrogen on contact with moist metals. Closed containers may rupture violently.
Source: Hazardous Substances Data Bank (HSDB)
Fire and explosion
Permonosulfonic acid was being prepared by reacting chlorosulfonic acid & 90% hydrogen peroxide. A sample was stored overnight at 0 °C, then removed to test tube rack. In 10 minutes it exploded.
Source: HSDB
10 · Handling and storage
Chlorosulfonic acid storage and handling
Chlorosulfonic acid safe storage
Separated from food and feedstuffs. See Chemical Dangers. Dry. Well closed.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Chlorosulfonic acid storage conditions
KEEP TIGHTLY CLOSED.
Source: Hazardous Substances Data Bank (HSDB)
Chlorosulfonic acid incompatible materials
Mixing chlorosulfonic acid with either 28% ammonia, creosote oil, 36% hydrochloric acid or 48.7% hydrofluoric acid, 70% nitric acid, 2-nitropropane or 96% sulfuric acid in a closed container caused the temperature & pressure to increase. It is dangerous in contact with combustible materials, nitrates, chlorates, metallic powders, carbides, picrates & fulminates.
Source: Hazardous Substances Data Bank (HSDB)
Planning storage for a mix of chemicals? Check Chlorosulfonic acid in the storage compatibility matrix →
11 · Transport
Chlorosulfonic acid UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
Chlorosulfonic acid under UN 1754 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| CHLOROSULPHONIC ACID (with or without sulphur trioxide) | 8 | C1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 8 is “Corrosive substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Chlorosulfonic acid (with or without sulfur trioxide) | 8 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 8 is “Corrosive material” (49 CFR 173.2).
12 · Questions
Chlorosulfonic acid — frequently asked questions
What is the CAS number of Chlorosulfonic acid?
The CAS number of Chlorosulfonic acid is 7790-94-5. Its EC number is 232-234-6.
What is the chemical formula of Chlorosulfonic acid?
The molecular formula of Chlorosulfonic acid is ClHO3S and its molecular weight is 116.53 g/mol.
What does a Chlorosulfonic acid label have to show?
Under CLP Annex VI the label for Chlorosulfonic acid carries the pictograms Corrosion and Exclamation mark and the signal word is Danger.
Is Chlorosulfonic acid flammable?
CLP Annex VI assigns Chlorosulfonic acid no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Chlorosulfonic acid a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Chlorosulfonic acid. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the boiling point of Chlorosulfonic acid?
The boiling point reported for Chlorosulfonic acid is 155 °C (311 °F), at 760 mmHg (CAMEO).
What is the melting point of Chlorosulfonic acid?
The melting point reported for Chlorosulfonic acid is -80 °C (-112 °F) (HSDB).
How should Chlorosulfonic acid be stored?
KEEP TIGHTLY CLOSED. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Chlorosulfonic acid
Keep going: substances starting with C, or search the whole database by name, CAS number, pictogram or signal word.