Selenium dioxide

Structural formula
General
Surname	Selenium dioxide
other names	Selenium (IV) oxide Selenic anhydride
Molecular formula	SeO 2
Brief description	white, hygroscopic needles
External identifiers / databases
CAS number 7446-08-4 EC number 231-194-7 ECHA InfoCard 100.028.358 PubChem 24007 Wikidata Q411386
properties
Molar mass	110.96 g · mol -1
Physical state	firmly
density	3.95 g cm −3
Sublimation point	315 ° C
Vapor pressure	16 h Pa (70 ° C)
solubility	soluble in water (384 g l −1 at 14 ° C)
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 301-331-373-410 P: 273-304 + 340-309 + 310-314
MAK	0.02 mg m −3
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Selenium dioxide (SeO ₂ ) is a solid which was from 315 ° C sublimes . It forms z. B. in the combustion of elemental selenium (Se) with oxygen .

Other oxides of selenium are selenium monoxide (SeO) and selenium trioxide (SeO ₃ ).

properties

Selenium dioxide forms shiny, white, sublimable needles. It crystallizes tetragonal , space group P 4 ₂ / mbc (space group no. 135) with the lattice parameters a = 8.36 and b = 5.06 Å at 286 K. When heated under pressure, an orange-yellow melt forms.

Selenium dioxide is readily soluble in water and has a hygroscopic effect . With water it forms selenous acid (H ₂ SeO ₃ ), a medium-strength acid, the salts of which are called selenites or oxoselenates (IV). This has a less reducing effect than the related sulfurous acid , but in an acidic environment it is an oxidizing agent:

${\displaystyle \mathrm {\ H_{2}SeO_{3}+4\ H^{+}+4\ e^{-}\rightleftharpoons \ Se+3\ H_{2}O\qquad {\mathit {E}}^{\circ }=+0,74\ V\quad (pH=0)} }$

Selenium dioxide is just as easily soluble in alcohol and concentrated sulfuric acid .

With concentrated, strong acids selenium dioxide can hydrolysis-sensitive selenium (IV) compounds such. B. form selenium oxychloride (SeOCl ₂ ).

Manufacturing

Selenium (IV) oxide is produced directly from the elements selenium and oxygen or by removing water from selenic acid .

${\displaystyle \mathrm {Se+O_{2}\longrightarrow \ SeO_{2}} }$

${\displaystyle \mathrm {H_{2}SeO_{3}\longrightarrow \ SeO_{2}+H_{2}O} }$

use

Selenium dioxide is used as an oxidizing agent in the synthesis of organic substances such as. B. the Riley oxidation used.

When severe forms of dandruff are present, selenium dioxide is used as an additive in shampoos.

safety instructions

Like selenium and its compounds, selenium dioxide is highly toxic. The MAK value is 0.02 mg / m³ (measured as the inhalable aerosol fraction). It can be absorbed through the intact skin. Required work protection: dust mask, rubber gloves, suction and ventilation at the workplace.

Individual evidence

1. ↑ ^{a b c} Entry on selenium dioxide. In: Römpp Online . Georg Thieme Verlag, accessed on July 14, 2014.
2. ↑ ^{a b c d e f g} Entry on selenium dioxide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
3. ↑ avantorinc: MSDS Selenium dioxide
4. ↑ K. Stahl, JP Legros, J. Galy: The crystal structure of SeO ₂ at 139 and 286 K. In: Zeitschrift für Kristallographie , 202, 1992, pp. 99-107, doi : 10.1524 / zkri.1992.202.14.99 .
5. ↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 428-429.