Selenium trioxide is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula
Se O3. It is white, hygroscopic solid. It is also an
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...
and a
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
. It is of academic interest as a precursor to Se(VI) compounds.
[Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier ]
Preparation
Selenium trioxide is difficult to prepare because it is unstable with respect to the dioxide:
:2 SeO
3 → 2 SeO
2 + O
2
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
Selenic acid is the inorganic compound with the formula . It is an oxoacid of selenium, and its structure is more accurately described as . It is a colorless compound. Although it has few uses, its derivative sodium selenate is used in the prod ...
with
phosphorus pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4 O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydra ...
at 150–160 °C. Another method is the reaction of liquid
sulfur trioxide
Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...
with
potassium selenate
Potassium selenate, , is an odorless, white solid that forms as the potassium salt of selenic acid.
Preparation
Potassium selenate is produced by the reaction of selenium trioxide and potassium hydroxide.
:
Alternatively, it can be made by tr ...
.
:SO
3 + K
2SeO
4 → K
2SO
4 + SeO
3
Reactions
In its chemistry SeO
3 generally resembles
sulfur trioxide
Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...
, SO
3, rather than
tellurium trioxide
Tellurium trioxide ( Te O3) is an inorganic chemical compound of tellurium and oxygen. In this compound, tellurium is in the +6 oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all ...
, TeO
3.
At 120 °C SeO
3 reacts with
selenium dioxide
Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.
Properties
Solid SeO2 is a one-dimensional polymer, the chain consisting of alternating seleniu ...
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. ]
:SeO
3 + SeO
2 → Se
2O
5
It reacts with
selenium tetrafluoride
Selenium tetrafluoride ( Se F4) is an inorganic compound. It is a colourless liquid that reacts readily with water. It can be used as a fluorinating reagent in organic syntheses (fluorination of alcohols, carboxylic acids or carbonyl compounds) an ...
to form
selenoyl fluoride
Selenoyl fluoride, selenoyl difluoride, selenium oxyfluoride, or selenium dioxydifluoride is a chemical compound with the formula SeO2F2.
Structure
The shape of the molecule is a distorted tetrahedron with the O-Se-O angle being 126.2°, the O-S ...
, the selenium analogue of
sulfuryl fluoride
Sulfuryl fluoride (also spelled ''sulphuryl fluoride'') is an inorganic compound with the chemical formula, formula SO2F2. It is an easily condensed gas and has properties more similar to sulfur hexafluoride than sulfuryl chloride, being resistant ...
:2SeO
3 + SeF
4 → 2SeO
2F
2 + SeO
2
As with SO
3 adducts are formed with
Lewis base
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
s such as
pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...
,
dioxane
1,4-Dioxane () is a heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers ( 1,2- ...
and
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...
.
With
lithium oxide
Lithium oxide ( O) or lithia is an inorganic chemical compound. It is a white solid. Although not specifically important, many materials are assessed on the basis of their Li2O content. For example, the Li2O content of the principal lithium miner ...
and
sodium oxide
Sodium oxide is a chemical compound with the formula Na2 O. It is used in ceramics and glasses. It is a white solid but the compound is rarely encountered. Instead "sodium oxide" is used to describe components of various materials such as glass ...
it reacts to form salts of Se
VIO
54− and Se
VIO
66−:
[Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, ] With Li
2O, it gives Li
4SeO
5, containing the trigonal pyramidal anion Se
VIO
54− with equatorial bonds, 170.6–171.9 pm; and longer axial Se−O bonds of 179.5 pm. With Na
2O it gives Na
4SeO
5, containing the square pyramidal Se
VIO
54−, with Se−O bond lengths ranging from range 172.9 → 181.5 pm, and Na
12(SeO
4)
3(SeO
6), containing octahedral Se
VIO
66−. Se
VIO
66− is the conjugate base of the unknown orthoselenic acid (Se(OH)
6).
Structure
In the solid phase SeO
3 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.
SeO
3 in the gas phase consists of tetramers and monomeric SeO
3 which is trigonal planar with an Se−O bond length of 168.78 pm.
References
Further reading
*
*
{{DEFAULTSORT:Selenium Trioxide
Oxides
Selenium(VI) compounds
Oxidizing agents
Interchalcogens