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Sulfates and sulfur salts

Sulfur trioxide

Also known as Sulphur trioxide, Sulfur oxide (SO3), Sulfan

CAS 7446-11-9Formula O3SMolar mass 80.06 g/molEC 231-197-3
GHS signal word: Danger. Pictograms: Corrosive, Acute toxicity (severe), Harmful or irritant, Serious health hazard 28 suppliers listed
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Sulfur trioxide chemical structure, O3S, CAS 7446-11-9
2D chemical structure

Key facts

What buyers check first

All properties
Appearance
White needles
Melting point
62.2 °C
Boiling point
44.8 °C
Density
Critical density: 0.630 g/cm³
Solubility
Slowly very sol in aqueous, and sol in 100 parts water at room temp
HS code
283220
Category
Sulfates and sulfur salts
UN number
UN 1829
Illustrative photo, colourless crystals beside a jumbo bulk bag in a chemical plant
Typical packagingIllustrative packaging image, not the actual product

What is Sulfur trioxide?

Plain description, key identifiers and synonyms

Sulfur trioxide is a sulfur oxide.

Identifiers

Registry numbers, names and line notations, tap to copy

IUPAC name
sulfur trioxide
CAS number
7446-11-9 CAS number cross-checkedOther or deprecated CAS: 12210-38-7
EC number
231-197-3
Molecular formula
O3S
UNII
HH2O7V4LYD
InChIKey
AKEJUJNQAAGONA-UHFFFAOYSA-N
InChI
InChI=1S/O3S/c1-4(2)3
SMILES (canonical and isomeric)
O=S(=O)=O

Synonyms

  • Sulphur trioxide
  • Sulfur oxide (SO3)
  • Sulfan
  • Sulfuric oxide
  • Sulfur trioxide, stabilized
  • Sulfuric anhydride
  • Sulfite radical anion
  • Sulfur trioxide, contains stabilizer, >=99%
  • Nisso sulfan
  • Trioxo-lambda~6~-sulfane
  • [SO3]

Physical and chemical properties

Measured values and descriptors computed from the structure

Physical and chemical properties

Measured values, check the supplier specification for your grade

Appearance
White needlesexp.
Melting point
62.2 °Cexp.
Boiling point
44.8 °Cexp.
Density
Critical density: 0.630 g/cm³exp.
Solubility
Slowly very sol in aqueous, and sol in 100 parts water at room tempexp.
Vapour pressure
73 mm Hg at 25 °C /alpha-form/exp.

Values vary by grade. Ask suppliers for the COA or TDS of the batch you buy.

Computed descriptors

Calculated from the structure, useful for screening and formulation

Molecular weight
80.06 g/molcalc.
Exact mass
79.9568 Dacalc.
LogP (octanol/water)
-1calc.
Topological polar surface area
51.21 Ųcalc.
Hydrogen bond donors
0calc.
Hydrogen bond acceptors
3calc.
Rotatable bonds
0calc.
Heavy atoms
4calc.
Rings
0calc.
Aromatic rings
0calc.
Fraction sp3 carbons
0calc.
Formal charge
0calc.
Stereocentres
0calc.

Calculated for screening. Confirm critical figures with the supplier.

Safety and hazards

GHS classification summary, not a safety data sheet

GHS signal word
Danger
GHS05: Corrosive
Corrosive
GHS06: Acute toxicity (severe)
Acute toxicity (severe)
GHS07: Harmful or irritant
Harmful or irritant
GHS08: Serious health hazard
Serious health hazard
GHS09: Hazardous to the environment
Hazardous to the environment

Hazard statements

  • H314Causes severe skin burns and eye damage.
  • H318Causes serious eye damage.
  • H330Fatal if inhaled.
  • H335May cause respiratory irritation.
  • H351Suspected of causing cancer.
  • H411Toxic to aquatic life with long lasting effects.
Precautionary statements (24)
  • P203Obtain, read and follow all safety instructions before use.
  • P260Do not breathe dust, fume, gas, mist, vapours or spray.
  • P261Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P264Wash skin thoroughly after handling.
  • P264 + P265Wash skin thoroughly after handling. Do not touch eyes.
  • P271Use only outdoors or in a well-ventilated area.
  • P273Avoid release to the environment.
  • P280Wear protective gloves, protective clothing, eye protection and face protection.
  • P284In case of inadequate ventilation wear respiratory protection.
  • P301 + P330 + P331If swallowed: Rinse mouth. Do not induce vomiting.
  • P302 + P361 + P354If on skin: Take off immediately all contaminated clothing. Immediately rinse with water for several minutes.
  • P304 + P340If inhaled: Remove person to fresh air and keep comfortable for breathing.
  • P305 + P354 + P338If in eyes: Immediately rinse with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P316Get emergency medical help immediately.
  • P317Get medical help.
  • P318If exposed or concerned, get medical advice.
  • P319Get medical help if you feel unwell.
  • P320Specific treatment is urgent (see supplemental first aid instructions on the label).
  • P321Specific treatment (see supplemental first aid instructions on the label).
  • P363Wash contaminated clothing before reuse.
  • P391Collect spillage.
  • P403 + P233Store in a well-ventilated place. Keep container tightly closed.
  • P405Store locked up.
  • P501Dispose of contents and container in accordance with local regulations.
UN number
UN 1829
Transport hazard class
8
Packing group
I

GHS classification summary, not a safety data sheet (SDS). Classifications can differ by supplier, grade and concentration. Always check the supplier's SDS.

Full safety data and first aid

Sulfur trioxide suppliers

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All 28 suppliers
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Where suppliers are based

28 suppliers in 6 countries

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Sulfur trioxide price

Indicative price range per kg from live supplier offers

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Uses and applications

What the substance is used for, by industry and function

Intermediate in sulfuric acid manufacture, in sulfonations for formation of addition cmpd with amines, in the manufacture of explosives.

Sulfonation of organic compounds, especially nonionic detergents, solar energy collectors.

Production of detergents, as a raw material for chlorosulfuric acid and 65% oleum. Has been added to cooled combustion gases at many coal burning power plants to improve dust removal in electrostatic precipitators.

Sulfur trioxide is used as such for preparing sulfonated oils, and alkyl arenesulfonate detergents.

Used as a powerful, but generally indiscriminate oxidizing agent, however, it will selectively oxidize pentachlorotoluene and similar compounds to the alcohol.

Functional uses

  • Binder

How it is made

Prepared by the contact process, for example, by the action of oxygen on sulfur dioxide in the presence of catalysts such as platinized asbestos, platinized magnesium sulfate, ferric oxide or vanadium compounds.

Liquid sulfur trioxide is produced by heating oleum in a boiler to generate SO3 gas which is then condensed.

May be prepared in the laboratory by heating fuming sulfuric acid and collecting the sublimate in a cooled receiver. If the vapor is condensed above 27 °C, the gamma form is obtained as a liquid. If the vapor is condensed below 27 °C and in the presence of a trace of moisture, a mixture of all 3 forms is obtained. The 3 forms can be separated by fractional distillation.

Regulatory status

Inventories, regulations and trade controls that list this substance

United States

  • TSCA inventory (USA)
    Status: Active in US commerce

HS code and trade data

Customs classification and reported world trade statistics

Global trade

World import and export statistics for the HS code Sulfur trioxide is traded under.

HS 2832.20Indicative HS code

Sulphites, thiosulphates, other sulphites

World exports in 2024
$39.4M
−42.1% vs 2023, imports $68.4M
2019 to 2024
Top exporters
  1. United States50.3%
  2. United Kingdom8.7%
  3. India * partner reported7.1%
Top importers
  1. Mexico24.8%
  2. Spain9.3%
  3. Turkey6.2%

* Partner reported figures, a lower bound.

Reported customs values in USD, not prices.Full trade data

The HS code shown for Sulfur trioxide is indicative (it was assigned by structure rules). Confirm the classification with your customs broker before shipping.

Frequently asked questions

Quick answers about Sulfur trioxide, based on the data on this page

What is Sulfur trioxide?

Sulfur trioxide is a sulfur oxide.

What is the CAS number of Sulfur trioxide?

The CAS registry number of Sulfur trioxide is 7446-11-9. Other or deprecated CAS numbers: 12210-38-7.

What is the molecular formula and weight of Sulfur trioxide?

The molecular formula of Sulfur trioxide is O3S and its molar mass is 80.06 g/mol.

What is Sulfur trioxide used for?

Intermediate in sulfuric acid manufacture, in sulfonations for formation of addition cmpd with amines, in the manufacture of explosives. Sulfonation of organic compounds, especially nonionic detergents, solar energy collectors. Production of detergents, as a raw material for chlorosulfuric acid and 65% oleum.

Is Sulfur trioxide hazardous?

Sulfur trioxide carries the GHS signal word "Danger". Main hazards: causes severe skin burns and eye damage, causes serious eye damage, fatal if inhaled. This summary is not an SDS, always read the supplier safety data sheet.

What is the HS code of Sulfur trioxide?

Sulfur trioxide is usually classified under HS code 283220 (Sulphites, thiosulphates, other sulphites). This is indicative, confirm it with your customs broker before shipping.

Where can I buy Sulfur trioxide?

CompoundList lists 28 suppliers of Sulfur trioxide in United States, India, China, United Kingdom and 2 more. Send one free request to get and compare quotes. Your contact details stay private until you accept a quote.

Where can I buy Sulfur trioxide in India?

10 suppliers in India list Sulfur trioxide on CompoundList. Filter the suppliers list by country and send a request to compare prices, grades and delivery times.

What is the price of Sulfur trioxide?

Suppliers quote Sulfur trioxide on request because prices depend on grade, purity, quantity and destination. A free request on CompoundList gets you several quotes to compare.

Guides for buyers

Practical guides that help when you source, ship or handle Sulfur trioxide

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Data last updated 7 Oct 2026. Details may have changed, please confirm them with the supplier. Report an error on this page
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