Molybdenum (VI) oxide

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Crystal structure
Crystal structure of molybdenum (VI) oxide
__ Mon 6+      __ O 2−
Crystal system

orthorhombic

Space group

Pbnm (No. 62, position 3)Template: room group / 62.3

Lattice parameters
  • a = 392 pm
  • b = 1394 pm
  • c = 366 pm
General
Surname Molybdenum (VI) oxide
other names
  • Molybdenum trioxide
  • Molybdic anhydride
  • Water lead earth
Ratio formula MoO 3
Brief description

yellow odorless solid

External identifiers / databases
CAS number 1313-27-5
EC number 215-204-7
ECHA InfoCard 100,013,823
PubChem 14802
Wikidata Q416416
properties
Molar mass 143.93 g mol −1
Physical state

firmly

density

4.7 g cm −3

Melting point

795 ° C

boiling point

1155 ° C

solubility

poor in water (0.49 g l −1 at 28 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
08 - Dangerous to health 07 - Warning

Caution

H and P phrases H: 319-335-351
P: 305 + 351 + 338-308 + 313
MAK

repealed as carcinogenic

Toxicological data
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Molybdenum (VI) oxide is a powdery colorless compound that is left behind when many molybdenum compounds are roasted .

history

In 1778 Carl Wilhelm Scheele succeeded in producing molybdenum (VI) oxide from molybdenum luster by treatment with nitric acid . In 1782 Peter Jacob Hjelm reduced the oxide to elemental molybdenum with coal .

Occurrence

It occurs naturally in the form of the rare mineral molybdite .

Extraction and presentation

Molybdenum (VI) oxide is obtained industrially by oxidizing molybdenum (IV) sulfide :

In the laboratory, it can also be obtained by reacting ammonium heptamolybdate and nitric acid or from sodium molybdate and perchloric acid, whereby molybdenum (VI) oxide dihydrate is formed:

The resulting dihydrate easily converts to the monohydrate. Both hydrates are pale yellow in color when pure. Above 450 ° C these are converted to anhydride.

properties

Sublimated needle-like crystals of molybdenum (VI) oxide

Molybdenum (VI) oxide is a white powder that turns yellow when heated and becomes colorless again when it cools. It has the ratio formula MoO 3 , a melting point of 795 ° C and a boiling point of 1155 ° C. Molybdenum (VI) oxide is sparingly soluble in water, but changes into molybdate ions MoO 4 2− in alkaline solution . In dilute solution can be this by acidification into the molybdic acid H 2 MoO 4 transfer.

It has a relatively high vapor pressure. It therefore sublimes noticeably from approx. 700 ° C, forming shiny, colorless crystalline tinsel.

Molybdenum (VI) oxide has an orthorhombic crystal structure . It consists of layers of distorted MoO 6 octahedra in an orthorhombic crystal. The octahedra are connected at the edges and form chains that are connected by oxygen atoms and form layers.

use

Molybdenum (VI) oxide is the starting material for the synthesis of most other molybdenum compounds, it is used as an enamel additive and for the production of pure molybdenum (e.g. by reduction with hydrogen).

It is also a catalyst (molybdenum trioxide powder on aluminum oxide ) for hydroforming, alkylation, desulphurisation and cracking processes in the petrochemical industry and in the production of acrylonitrile .

safety instructions

The IARC classified molybdenum (VI) oxide as a possible carcinogen in 2017.

Individual evidence

  1. a b c d e f g h i Georg Brauer (Ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1544.
  2. a b c d e f g h i j Entry on molybdenum (VI) oxide in the GESTIS substance database of the IFA , accessed on February 7, 2019(JavaScript required) .
  3. Entry on Molybdenum trioxide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  4. Heynes, JBB; Cruywagen, JJ "Yellow Molybdenum (VI) Oxide Dihydrate" Inorganic Syntheses, 1986, volume 24, pp. 191. ISBN 0-471-83441-6 .
  5. "Carcinogenicity of welding, molybdenum trioxide, and indium tin oxide" In: Lancet Oncology, 18: 581-582, 2017.