Selenium dioxide



Selenium dioxide

General
Other names Selenium(IV) oxide
Selenium dioxide
Molecular formula O2
Molar mass 110.96 g/mol
Appearance White crystalline solid
CAS number [7446-08-4]
Properties
Density and phase 3.95 g/cm3, solid
water 3.950 g/100 ml (25 °C)
Boiling point 315 °C sublimes
Acidity (pKa) 2.62 (H2SeO3 ⇌ HSeO3− + H+)
8.32 (HSeO3− ⇌ SeO32− + H+)
Structure
Coordination
geometry 		trigonal
Crystal structure chain structure
Hazards
EU classification Toxic (T)
Dangerous for
the environment (N)
NFPA 704
0
3
0
 
R-phrases R23/25, R33, R50/53
S-phrases S61
U.S. Permissible
Exposure Limit 		5 ppm
IDLH (NIOSH) 100 ppm
Flash point non-flammable
RTECS number WS4550000
Supplementary data page
Structure and
properties 		εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data MS
Related compounds
Other cations Tellurium dioxide
Related compounds Selenium trioxide
Selenous acid
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Selenium dioxide is the selenium.

Properties

Solid SeO2 is a one-dimensional TeO2 is a cross-linked polymer.

SeO2 is considered an acidic oxide: it dissolves in water to form selenous (selenious) acid. Often the term selenous (selenious) acid and selenium dioxide are used interchangeably. It reacts with base to form selenite SeO32-:

SeO2 + 2 NaOH → Na2SeO3 + H2O

Preparation

Selenium dioxide is prepared by oxidation of hydrogen peroxide, but perhaps the most convenient preparation is by the dehydration of selenous acid.

3Se + 4HNO3 + H2O → 3H2SeO3 + 4NO
H2SeO3 ⇌ SeO2 + H2O

Uses

Organic synthesis

SeO2 is an important reagent in cyclohexanone gives cyclohexane-1,2-dione.[3]

It is also renown as a reagent for "allylic" oxidation,[4] a reaction that entails the conversion

R2C=CR'-CHR"2 + [O] → R2C=CR'-C(OH)R"2

(where R, R', R" are alkyl or aryl).

As a colorant

Selenium dioxide imparts a red colour to glass: it is used in small quantities to counteract the blue colour due to cobalt impurities and so to create (apparently) colourless glass. In larger quantities, it gives a deep ruby red colour.

Selenium dioxide is the active ingredient in some cold-blueing solutions.

It is also used as a toner in photographic developing.


References

  1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ Ronzio, A. R.; Waugh, T. D. (1955). "Glyoxal Bisulfite". Org. Synth.; Coll. Vol. 3: 438. 
  3. ^ Hach, C. C. Banks, C. V.; Diehl, H. (1963). "1,2-Cyclohexanedione Dioxime". Org. Synth.; Coll. Vol. 4: 229. 
  4. ^ Coxon, J. M.; Dansted, E.; Hartshorn, M. P. (1988). "Allylic Oxidation with Hydrogen Peroxide–Selenium Dioxide: trans-Pinocarveol". Org. Synth.; Coll. Vol. 6: 946. 

Further reading

  • Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn.) New York:Wiley-Interscience. ISBN 0-471-19957-5.
  • Lide, D. R. (Ed.) (2002). CRC Handbook of Chemistry and Physics (83rd Edn.). Boca Raton (FL):CRC Press. ISBN 0-8493-0483-0. 
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Selenium_dioxide". A list of authors is available in Wikipedia.