Sulfur trioxide

Sulfur trioxide is used as an intermediate in the manufacture of sulphuric acid and oleum for sulphonation, in particular, of dyes and dye-stuffs, and for the production of anhydrous nitric acid and explosives. Solid Sulfur trioxide is marketed under such names as Sulphan and Triosul, and is used primarily for sulphonation of organic acids. Sulphur tetrafluoride is a fluorinating agent. Sulphur hexafluoride serves as a gaseous insulator in high-voltage electric installations. Sulphyryl fluoride is used as an insecticide and a fumigant.Sulfonation of organic compounds, especially nonionic detergents, solar energy collectors. It is usually generated in the plant where it is to be used.
Sulfur trioxide, S03, also known as sulfuric anhydride, needles or polymer, exists in a number of modifications that differ in molecular species and crystalline form. It has a white,ice-like modification that melts at 16°C (61°F) and two other as bestos-like forms that melt at the higher temperatures of 33 and 62°C (90 and 144 °F). The colorless liquid or gas form has irritating, toxic fumes and boils at 45 °C (112 °F).