Barium pyrosulfate has the molecular formula of
BaS2O7 and the molecular weight of 313.4578 g/mol.
There is no data concerning this salt is available either
in patents, scientific or technical literature, or in reference
books. Indeed, it has been stated that “This salt
does not existdit was first prepared by J.J. Berzelius in
1843 ..” “It is decomposed by water . Apart from
some doubt as to its precise structure, the compound
is of little interest, and has never been more than a chemical
curiosityd1933”. However, this salt can be prepared
by the solid-state reaction of ammonium pyrosulfate
with barium chloride:
BaCl2 + (NH4)2S2O7 + heat
? BaS2O7 + 2HCl(gas) + 2NH3(gas)
However, a better method of preparation involves
reaction of the sulfate with fuming sulfuric acid
(Oleum):
BaSO4
+H2SO4?BaS2O7
+H2O
The syrupy solution is heated to >150–175°C to drive
off the water and allow crystals to appear. Once formed,
barium pyrosulfate is stable to about 720°C where it
decomposes to the sulfate plus sulfur trioxide gas. It
can also be prepared by heating the persulfate:
2BaS2O8 + heat ? 2BaS2O7 + O2
The persulfate is also called peroxodisulfate. Further
heating will form the sulfate, BaSO4 plus sulfur trioxide.
It is expected that this salt will be unstable in water.
However, the solubility of this salt has not been
reported.
