sulfur trioxide

References

sulfur trioxide

chemical compound

Also known as: sulphur trioxide

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 23, 2026

Quick Summary

Sulfur trioxide (SO₃) is a compound of sulfur and oxygen. It is a colorless substance that can exist as a volatile liquid or in solid forms. Sulfur trioxide is the acid anhydride of sulfuric acid, meaning it reacts with water to form sulfuric acid, releasing significant heat.12

It is produced industrially by reacting sulfur dioxide with oxygen, often using catalysts, and is a key intermediate in the manufacture of sulfuric acid. Sulfur trioxide is highly corrosive and a powerful oxidizing agent, capable of igniting combustible materials upon contact. It is used primarily as a sulfonating and sulfating agent, particularly in the production of detergents.132

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

oxide
Nonmetal oxides
First, oxides such as sulfur trioxide (SO₃) and dinitrogen pentoxide (N₂O₅), in which the nonmetal exhibits one of its common oxidation numbers, are known as acid anhydrides. These oxides react with water to form oxyacids, with no change in the oxidation number of the nonmetal; for example,N₂O₅ +…
Read More
First, oxides such as sulfur trioxide (SO₃) and dinitrogen pentoxide (N₂O₅), in which the nonmetal exhibits one of its common oxidation numbers, are known as acid anhydrides. These oxides react with water to form oxyacids, with no change in the oxidation number of the nonmetal; for example,N₂O₅ +…
Read More

contact process
…hot catalyst, unite to form sulfur trioxide, which in turn combines with water to make sulfuric acid.
Read More
…hot catalyst, unite to form sulfur trioxide, which in turn combines with water to make sulfuric acid.
Read More

sulfur dioxide
…the preparation of sulfuric acid, sulfur trioxide, and sulfites, sulfur dioxide also is used as a disinfectant, a refrigerant, a reducing agent, a bleach, and a food preservative, especially in dried fruits.
Read More
…the preparation of sulfuric acid, sulfur trioxide, and sulfites, sulfur dioxide also is used as a disinfectant, a refrigerant, a reducing agent, a bleach, and a food preservative, especially in dried fruits.
Read More

chemical industry
Chamber process
…with oxygen to form the trioxide, which is then combined with water. A technique to form the trioxide, called the chamber process, developed in the early days of the operation of the Leblanc process. In this technique the reaction between sulfur dioxide and oxygen takes place in the presence of…
Read More
…with oxygen to form the trioxide, which is then combined with water. A technique to form the trioxide, called the chamber process, developed in the early days of the operation of the Leblanc process. In this technique the reaction between sulfur dioxide and oxygen takes place in the presence of…
Read More