selenium trioxide

{{chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 464388785

| Name = Selenium trioxide

| ImageFileL1 = Selenium trioxide.svg

| ImageNameL1 = Structural formula of the monomer as found in the gas phase

| ImageFileR1 = Selenium-trioxide-3D-spacefill.png

| ImageNameR1 = Space-filling model of the monomer as found in the gas phase

| Reference =

{{Cite book

| last = Lide

| first = David R.

| year = 1998

| title = Handbook of Chemistry and Physics

| edition = 87

| location = Boca Raton, Florida

| publisher = CRC Press

| isbn = 0-8493-0594-2

| pages = 4–81

}}

| OtherNames =

|Section1={{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChemSpiderID = 103019

| InChI = 1/O3Se/c1-4(2)3

| InChIKey = VFLXBUJKRRJAKY-UHFFFAOYAC

| SMILES = O=[Se](=O)=O

| SMILES_Comment = monomer

| SMILES1 = O=[Se]0(=O)O[Se](=O)(=O)O[Se](=O)(=O)O[Se](=O)(=O)O0

| SMILES1_Comment = cyclic tetramer

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChI = 1S/O3Se/c1-4(2)3

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = VFLXBUJKRRJAKY-UHFFFAOYSA-N

| CASNo_Ref = {{cascite|changed|??}}

| CASNo = 13768-86-0

| PubChem = 115128

}}

|Section2={{Chembox Properties

| Formula = SeO₃

| MolarMass = 126.96 g/mol

| Appearance = white hygroscopic crystals

| Density = 3.44 g/cm³

| Solubility = very soluble

| MeltingPtC = 118.35

| BoilingPt = sublimes

}}

|Section3={{Chembox Structure

| CrystalStruct = tetragonal

}}

|Section7={{Chembox Hazards

| GHS_ref={{cite web |title=C&L Inventory |url=https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/details/153441 |website=echa.europa.eu |access-date=16 December 2021}}

| GHSPictograms = {{GHS06}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|301|331|373|410}}

| PPhrases = {{P-phrases|}}

| NFPA-H = 4

| NFPA-F = 0

| NFPA-R = 2

| NFPA-S = OX

| LD50 = 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){{IDLH|7782492|Selenium compounds (as Se)}}

| LC50 = 13 mg/kg (pig, oral)
9.9 mg/kg (cow, oral)
3.3 mg/kg (goat, oral)
3.3 mg/kg (sheep, oral)

}}

Selenium trioxide is the inorganic compound with the formula Se O₃. 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.Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier {{ISBN|0123526515}}

Preparation

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

:2 SeO₃ → 2 SeO₂ + O₂

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. Another method is the reaction of liquid sulfur trioxide with potassium selenate.

:SO₃ + K₂SeO₄ → K₂SO₄ + SeO₃

Reactions

In its chemistry SeO₃ generally resembles sulfur trioxide, SO₃, rather than tellurium trioxide, TeO₃. The substance reacts explosively with oxidizable organic compounds.{{Sfn|Schmidt|Bornmann|Wilhelm|1963}}

At 120 °C SeO₃ reacts with selenium dioxide to form the Se(VI)-Se(IV) compound diselenium pentaoxide:Z. Žák "Crystal structure of diselenium pentoxide Se₂O₅" Zeitschrift für anorganische und allgemeine Chemie 1980, volume 460, pp. 81–85. {{doi|10.1002/zaac.19804600108}}

:SeO₃ + SeO₂ → Se₂O₅

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

:2SeO₃ + SeF₄ → 2SeO₂F₂ + SeO₂

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⁻:Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Francesco A. Devillanova, Royal Society of Chemistry, 2007, {{ISBN|9780854043668}} 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 172.9 → 181.5 pm, and Na₁₂(SeO₄)₃(SeO₆), containing octahedral Se^VIO₆⁶⁻. Se^VIO₆⁶⁻ is the conjugate base of the unknown orthoselenic acid (Se(OH)₆).

Structure

In the solid phase SeO₃ consists of cyclic tetramers, with an 8 membered (Se−O)₄ ring. Selenium atoms are 4-coordinate, bond lengths being Se−O bridging are 175 pm and 181 pm, non-bridging 156 and 154 pm.

SeO₃ in the gas phase consists of tetramers and monomeric SeO₃ which is trigonal planar with an Se−O bond length of 168.78 pm.{{cite journal|last1=Brassington|first1=N. J.|last2=Edwards|first2=H. G. M.|last3=Long|first3=D. A.|last4=Skinner|first4=M.|title=The pure rotational Raman spectrum of SeO₃|journal=Journal of Raman Spectroscopy|volume=7|issue=3|year=1978|pages=158–160|issn=0377-0486|doi=10.1002/jrs.1250070310|bibcode=1978JRSp....7..158B}}

selenium trioxide

Preparation

Reactions

Structure

References

Further reading