Nomenclature
CAS number: 7446-11-9
Sulfuric anhydride.
O
3S; mol wt 80.06.
O 59.95%, S 40.05%.
SO
3.
Description and references
Prepd by the contact process, i.e., by the action of oxygen on sulfur dioxide in the presence of catalysts
such as platinized asbestos, platinized magnesium sulfate, ferric
oxide, or vanadium compds. Extensive review and bibliography: Fairlie, Sulfuric Acid Manufacture, A.C.S. Monograph Series
no. 69 (New York, 1936). Exists in 3
modifications. May be prepd in the laboratory by heating fuming sulfuric
acid and collecting the sublimate in a cooled receiver. If the vapor
is condensed above 27°, the γ-form is obtained as a liquid. If the
vapor is condensed below 27° 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. The α-form is the stable modification,
the β- and γ-forms are metastable. Review of toxicology and human
exposure: Toxicological Profile for Sulfur
Trioxide and Sulfuric Acid (PB99-122038, 1998) 224 pp.
Properties
Corrosive; poisonous. Melted SO3 exists in the γ-form and on solidifying tends
to the α-form. The difference in vapor pressures explains the so-called “alpha
explosion” of sulfur trioxide. Heating of high-melting SO3 in glass vessels should be avoided to prevent possible shattering
of the container. Absolutely dry SO3 is not corrosive
to metals and shows no acid reaction. On exposure to air, it absorbs
moisture rapidly, emitting dense white fumes. Combines with water
with explosive violence (heat of dilution 504 cals/g) forming sulfuric
acid. Due to this avidity for water, SO3 chars many organic
substances. On contact with wood shavings the heat produced by dehydration
is sufficient to cause fire.Derivative
α-Form.
Properties
Asbestos-like needles, mp 62.3°. Vapor pressure at 25° = 73 mm.Derivative
β-Form.
Properties
Asbestos-like neeedles, mp 32.5°. Vapor pressure at 25° = 344 mm.Derivative
γ-Form.
Properties
Ice-like mass, mp 16.8° or liquid, d 1.9224. bp760 44.8°. Vapor pressure at 25° =
433 mm.Caution
Potential symptoms of overexposure
by inhallation are tooth erosion and respiratory tract irritation;
by ingestion are mouth and throat burns, gastric erosion; direct contact
may cause irritation or chemical burns of skin, eyes, respiratory
and gastrointestinal tracts. See PB99-122038.Use
Intermediate in sulfuric acid manuf; in sulfonations
for formation of addition compds with amines; in the manuf of explosives.