Selenium trioxide

Selenium trioxide

Identifiers
CAS Number	13768-86-0 N
3D model (Jmol)	Interactive image
ChemSpider	103019 Y
ECHA InfoCard	100.033.972
PubChem CID	115128
InChI InChI=1S/O3Se/c1-4(2)3 Y Key: VFLXBUJKRRJAKY-UHFFFAOYSA-N Y InChI=1/O3Se/c1-4(2)3 Key: VFLXBUJKRRJAKY-UHFFFAOYAC
SMILES O=[SeH2](=O)=O
Properties
Chemical formula	SeO3
Molar mass	126.96 g/mol
Appearance	white hygroscopic crystals
Density	3.44 g/cm3
Melting point	118.35 °C (245.03 °F; 391.50 K)
Boiling point	sublimes
Solubility in water	very soluble
Structure
Crystal structure	tetragonal
Hazards
EU classification (DSD)	not listed
Lethal dose or concentration (LD, LC):
LD50 (median dose)	7 mg/kg (rat, oral) 7.08 mg/kg (mouse, oral) 5.06 mg/kg (guinea pig, oral) 2.25 mg/kg (rabbit, oral) 13 mg/kg (horse, oral)
LC50 (median concentration)	13 mg/kg (pig, oral) 9.9 mg/kg (cow, oral) 3.3 mg/kg (goat, oral) 3.3 mg/kg (sheep, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Selenium trioxide is the inorganic compound with the formula SeO₃. It is white, hygroscopic solid. It is also an oxidizing agent and a Lewis acid. It is of academic interest as a precursor to Se(VI) compounds.

Selenium trioxide is difficult to prepare because it is unstable with respect to the dioxide:

It has been generated in a number of ways despite the fact that the dioxide does not combust under normal conditions. One method entails dehydration of anhydrous selenic acid with phosphorus pentoxide at 150-160 °C. The reaction of liquid sulfur trioxide with potassium selenate

In its chemistry SeO₃ generally resembles sulfur trioxide, SO₃, rather than tellurium trioxide, TeO₃.

At 120 °C SeO₃ reacts with selenium dioxide to form the Se(VI)-Se(IV) compound diselenium pentoxide:

It reacts with selenium tetrafluoride to form selenoyl fluoride, the selenium analogue of sulfuryl fluoride

As with SO₃ adducts are formed with Lewis bases such as pyridine, dioxane and ether.

With lithium oxide and sodium oxide it reacts to form salts of Se^VIO₅⁴⁻ and Se^VIO₆⁶⁻: With Li₂O, it gives Li₄SeO₅, containing the trigonal pyramidal anion Se^VIO₅⁴⁻ with equatorial bonds, 170.6-171.9 pm; and longer axial Se-O bonds of 179.5 pm. With Na₂O it gives Na₄SeO₅, containing the square pyramidal Se^VIO₅⁴⁻, with Se-O bond lengths ranging from range 1.729 → 1.815 pm, and Na₁₂(SeO₄)₃(SeO₆), containing octahedral Se^VIO₆⁶⁻. Se^VIO₆⁶⁻ is the conjugate base of the unknown orthoselenic acid (Se(OH)₆).