7446-11-9
sulfur trioxide
CAS: 7446-11-9
Molecular Formula: O3S
7446-11-9 - Names and Identifiers
7446-11-9 - Physico-chemical Properties
| Molecular Formula | O3S |
| Molar Mass | 80.06 |
| Density | 1.97g/mLat 25°C(lit.) |
| Melting Point | 16.8°C(lit.) |
| Boling Point | 44.8 °C |
| Water Solubility | reacts violently |
| Vapor Presure | 280 mm Hg ( 25 °C) |
| Vapor Density | 2.8 (vs air) |
| Appearance | colorless liquid |
| Merck | 13,9069 |
| Storage Condition | Indoors |
| Stability | Stable. Incompatible with organic materials, finely powdered metals, bases, water, cyanides and a wide variety of other chemicals. Reacts violently with water, oxygen and other chemicals |
| Physical and Chemical Properties | Colorless transparent oily liquid with strong irritating odor. melting point 16.83 ℃ boiling point 44.8 ℃ relative density 1.97(20 ℃) |
| Use | For organic synthesis, production of chlorosulfonic acid and sulfuric acid |
7446-11-9 - Risk and Safety
| Risk Codes | R45 - May cause cancer R8 - Contact with combustible material may cause fire R14 - Reacts violently with water R26 - Very Toxic by inhalation R34 - Causes burns R37 - Irritating to the respiratory system R35 - Causes severe burns |
| Safety Description | S53 - Avoid exposure - obtain special instructions before use. S17 - Keep away from combustible material. S26 - In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S36/37/39 - Wear suitable protective clothing, gloves and eye/face protection. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) S8 - Keep container dry. S25 - Avoid contact with eyes. S30 - Never add water to this product. |
| UN IDs | UN 1829 8/PG 1 |
| WGK Germany | 1 |
| RTECS | WT4830000 |
| Hazard Class | 8 |
| Packing Group | I |
7446-11-9 - Upstream Downstream Industry
| Raw Materials | sulfur dioxide Sulfur(α) Sulfuric acid Oxygen |
7446-11-9 - Nature
Open Data Verified Data
a colorless, transparent, oily liquid with a strong irritating odor. Relative density 1. 97 (20 ℃). Melting point 16. 83 °c. Boiling Point (101. 3kPa) 44.8 deg C. Strong oxidant, can be sulfur, phosphorus, carbon reduction. The dehydration effect of sulfuric acid and fuming sulfuric acid is stronger. The corrosion of gold dust than sulfuric acid, fuming sulfuric acid is weak.
Last Update：2025-06-10 22:55:16
7446-11-9 - Preparation Method
Open Data Verified Data
fuming sulfuric acid method: sulfur (or pyrite or other sulfur-containing substances) and dry air are burned in a sulfur incinerator to generate high-concentration sulfur dioxide gas, and sulfur trioxide is generated by catalytic oxidation, fuming sulfuric acid is obtained by absorption with sulfuric acid, and then sulfur trioxide gas is obtained by distillation. After cooling and compression liquefaction, liquid sulfur trioxide product is obtained.
Last Update：2022-01-01 11:03:51
7446-11-9 - Application
Open Data Verified Data
It is mainly used for sulfonation and sulfation of organic compounds. It is widely used as a reactant in the production of surfactants and ion exchange resins. It is also used in the synthesis of sulfonamides. For the production of dye intermediates, refined oil lubrication fraction.
Last Update：2025-08-19 16:24:40
7446-11-9 - Safety
Open Data Verified Data
see industrial sulfuric acid, liquid sulfur dioxide. The maximum allowable concentration of sulfur trioxide in air is 1mg/m3. Risk code: acid corrosion products. GB8.1 class 810100 UN N0.1829; IMDG Code page 8233. Class B1. Stable liquid sulfur trioxide transport technology and high concentration of fuming sulfuric acid is the same, to avoid the entry of water to prevent polymerization. In the production, storage and handling, must be completely sealed. The exhaust pipe of storage tank, loading tank and other equipment must be passed through an acid washing tower to prevent atmospheric moisture infiltration and sulfur trioxide overflow. For coagulation
Liquid sulfur trioxide at 16.8 °c shall be maintained at 30 °c during the processing stage, in the finished product storage tank and in the bulk supply tank. Barreled storage is only allowed for plants that allow curing. Liquid sulfur trioxide container, must not be washed with water, must be concentrated sulfuric acid to dissolve sulfur trioxide solid deposits. When there is a fire, the fire can be suppressed by a carbon dioxide fire. Also can be removed sand, quartz sand and soda. Firemen should wear gas masks and necessary protective equipment.
Last Update：2025-06-10 22:55:16
7446-11-9 - Reference Information
| NIST chemical information | information provided by: webbook.nist.gov (external link) |
| EPA chemical substance information | information provided by: ofmpeb.epa.gov (external link) |
| sulfur trioxide reacts with water | similar to sulfur dioxide, sulfur trioxide is also an acidic oxide with the properties of acidic oxides, it reacts with water to produce sulfuric acid, so we also call it "sulfur anhydride". The most important property in sulfur trioxide is its reaction with water, because it reacts with water to produce sulfuric acid, which is one of the steps in the industrial preparation of sulfuric acid. SO3 H2O = = H2SO4 in the reaction with water, while releasing a lot of heat, and even make water boiling, so generally do not use water to absorb sulfur trioxide, but with 98.3 of concentrated sulfuric acid to absorb sulfur trioxide, A small amount of water in the concentrated sulfuric acid can continue to absorb sulfur trioxide. |
| molecular structure | sulfur trioxide is a monomer in the gaseous state, the molecular shape is a plane triangle, the sulfur atom is centered, the bond angle is 120 °, the bond length of S-O is 1.43 × 10-10m, which is obviously characterized by a double bond (the single bond length of S-O is about 1.55 × 10-10m), in which the sulfur atom is in the sp2 hybrid state. In the liquid state, the monomer and trimer (SO3)3 are in equilibrium: the higher the temperature, the less the trimer. Solid sulfur trioxide mainly exists in two forms, one is fibrous (SO3)n, the other is ice-like structure of the trimer (SO3)3. |
| State at normal temperature and pressure | sulfur trioxide is also known as sulfuric anhydride, a high-valence oxide of sulfur, one of the products of the sulfuric acid industry. It is a colorless liquid with a boiling point of 44.8 ° C. At normal pressure and room temperature. Strong smoke in the atmosphere, the formation of difficult to settle sulfuric acid mist. An unusually intense reaction occurs with water to produce sulfuric acid, accompanied by an acid mist, and a large amount of heat is released. Sulfur trioxide was dissolved in 100% sulfuric acid to generate fumaric acid. Solid sulfur trioxide has three forms with melting points of 16.86 ℃, 30.4 ℃ and 62.2 ℃, respectively. The latter two are high molecular weight sulfur trioxide polymers, and the former is a mixture of monomolecules and trimers. The polymerization of liquid sulfur trioxide can be promoted by lowering the temperature in the presence of traces of water or sulfuric acid. When the polymerized sulfur trioxide is melted, an explosion is likely to occur because a higher vapor pressure has been generated before melting. |
| toxicity | see industrial sulfuric acid, liquid sulfur dioxide. The maximum allowable concentration of sulfur trioxide in air is 1 mg/m3. |
| Application | for sulfuric acid, chlorosulfonic acid, sulfamic acid, dimethyl sulfate, detergent and used as sulfonating agent in organic synthesis mainly used in sulfonation and sulfation of organic compounds. It is widely used as a reactant in the production of surfactants and ion exchange resins. It is also used in the synthesis of sulfonamides. For the production of dye intermediates, refined oil lubrication fraction. for organic synthesis, preparation of chlorosulfonic acid and sulfuric acid |
| production method | the fuming sulfuric acid method combusts sulfur (or pyrite or other sulfur-containing substances) with dry air in a sulfur incinerator, high-concentration sulfur dioxide gas is generated, and sulfur trioxide is generated by catalytic oxidation. Fuming sulfuric acid is obtained by absorption with sulfuric acid, and sulfur trioxide gas is obtained by distillation. S2 2O2 → 2SO22SO2 O2 → 2SO3 |
| category | corrosive article |
| toxicity grade | poisoning |
| Acute toxicity | inhalation-human TCL0: 30 mg/m3; Inhalation-guinea pig LC50: 50 mg/m3 |
| explosive hazard characteristics | high-heat explosion in water |
| flammability hazard characteristics | flammability in case of organic |
| storage and transportation characteristics | The warehouse is ventilated and dried at low temperature, separate storage of combustible materials |
| extinguishing agent | dry sand, carbon dioxide |
| Occupational Standard | TWA 1 mg/m3; Tel 2 mg/m3 |
| toxic substance data | information provided by: pubchem.ncbi.nlm.nih.gov (external link) |
Last Update：2024-04-09 02:00:11
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