Silver oxide 

Silver oxide
IUPAC name Silver oxide
Other names Silver rust
Argentous oxide
Molecular formula Ag2O
Identifiers
CAS number 20667-12-3
Properties
Molar mass 231.7148 g/mol
Ag = 93.1%, O = 6.9%
Appearance black/brown solid
Density 7.2 g/cm3, solid
Melting point

280°Ccitation needed (decomposition)
Solubility in water 0.0013 g/100 ml (20°C)
Ksp of AgOH 1.52 × 10-8 (20°C)
Acidity (pKa) -4
Structure
Crystal structure cubic
Hazards
MSDS Material Safety Data Sheet
Related compounds
Related compounds silver(I,III) oxide, AgO
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox references

Silver oxide is the chemical compound with the formula Ag2O. It is a fine black or dark brown powder that is used to prepare other silver compounds.

Contents

Preparation

Silver oxide is commercially available. It can be easily prepared by combining aqueous solutions of silver nitrate and an alkali hydroxide.1 Noteworthy is the fact that this reaction does not afford appreciable amounts of silver hydroxide due to the favorable energetics for the following reaction:2

2 AgOH → Ag2O + H2O K is large

Properties

Like most binary oxides, Ag2O is a three-dimensional polymer with covalent metal-oxygen bonding. It is therefore expected that Ag2O is insoluble in all solvents,3 except by reaction. It is also slightly soluble in aqueous solution due to the formation of the ion, Ag(OH)2– and possibly related hydrolysis products.4 It hydrolyzes only slightly in water (1 part in 40,000) and dissolves in ammonium hydroxide solution to give soluble derivatives.

A slurry of Ag2O is readily attacked by acids:

Ag2O + 2 HX → 2 AgX + H2O

where HX = HF, HCl, HBr, or HI, HO2CCF3. It will also react with solutions of alkali chlorides to precipitate silver chloride, leaving a solution of the corresponding alkali hydroxide.54

Like many silver compounds, silver oxide is photosensitive. It also decomposes at temperatures above 280 °C.3

Applications

Silver oxide is used in a silver-oxide battery. Silver oxide reacts easily with ligand precursors such as 1,3-disubstituted imidazolium or benzimidazolium salts to generate the corresponding N-heterocyclic carbene complexes. These silver complexes are useful as carbene-transfer agents, easily displacing labile ligands such as cyclooctadiene or acetonitrile. This is a common way of synthesizing transition metal carbene complexes.6

References

  1. ^ This publication gives the preparation of Ag2O and silver trifluoroacetate: "4-Iodoveratrole" Janssen, D. E.; Wilson, C. V. Organic Syntheses, Collected Volume 4, pp. 547 (1963). http://www.orgsyn.org/orgsyn/pdfs/CV4P0547.pdf
  2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  3. ^ a b Merck Index of Chemicals and Drugs, 14th ed. monograph 8521
  4. ^ a b Cotton, F. Albert; Wilkinson, Geoffrey (1966). Advanced Inorganic Chemistry (2nd Ed.). New York:Interscience.  Advanced Inorganic Chemistry by Cotton and Wilkinson, 2nd ed. p1042
  5. ^ General Chemistry by Linus Pauling, 1970 Dover ed. p703-704
  6. ^ Wang, H. M. J.; Lin, I. J. B. "Facile Synthesis of Silver(I)-Carbene Complexes. Useful Carbene Transfer Agents" Organometallics 1998, 17, 972-975. doi:10.1021/om9709704

See also

External links