Barium Thionates

Description

The "thionite" and "thionate" salts of barium include:
Barium dithionite=BaS2O4
Barium dithionate=BaS2O6
Barium tetrathionate=BaS4O6
Barium dithionite, BaS2O4, may be prepared by the reaction of barium chloride with sodium dithonite:
BaCl2+ Na2S2O4 ? BaS2O4+ 2NaCl
Alternatively, it may be prepared by the solid-state reaction of SO2 gas upon the sulfite:
Ba(HSO3)2(solid)+ SO2(gas)+ heat
? BaS2O4(solid)+H2O(gas)
This reaction could probably be carried out in solution as well. However, the reaction would be dependent upon the pH of the solution and a pH of about 5.0 would produce the hydrosulfite and then the dithionite:
BaCl2+ 2(NH4)2SO3+ SO2 ? BaS2O4+ 2NH4Cl+H2O
The description of the physical and chemical properties of this salt are completely lacking in the scientific and technological literature. Barium dithionite is mentioned in a few patents as a reducing agent. The older reference books like Sidgewick or Remy (1933 or 1950) do not list such a compound as being known. It has no CAS number and has no commercial value.
Barium dithionate, BaS2O6, has the molecular weight of 297.4538 g/mol. It has been prepared by the following method:
NH3(gas)+ SO2(gas)+H2O ? (NH4)2SO3(liq)
(NH4)2SO3(liq)+ MnO2(solid) ? MnS2O6(liq)
MnS2O6(liq)+ Ba(OH)2(solid)
?BaS2O6(liq)+ Mn(OH)2(solid)
In the first reaction, sulfur dioxide gas was passed through a cooled, continuously agitated solution to produce the ammonium compound. The solution was heated to remove excess sulfur dioxide. In the second reaction, theMnO2 was allowed to dissolve over a period of 2–5 h and was then diluted. The third reaction served to form the insoluble manganese hydroxide that was removed by filtration and the resulting solution was evaporated at a low temperature to form dihydrate crystals. On allowing the solution to evaporate at a moderate temperature, rhombic crystals are obtained. The product is a dihydrate, BaS2O6·2H2O. It is soluble in water at 24.4 g/100 ml (18°C) and 50.2 g/100 ml at 100°C. Its CAS number is 13845-17-5. It occurs as white crystals that decompose at about 145°C, its density is 4.54 g/ cm3, its solubility in water is 22.1 g/100 ml and it is slightly soluble in alcohol. When the dihydrate is heated to 90°C, loss of the two molecules of water of hydration occurs. On further heating, it decomposes to BaSO4:
BaS2O4+ heat ? BaSO4+ BaS
Barium tetrathionate, BaS4O6, has the molecular weight of grams per mole. Barium tetrathionate has been prepared by reaction of barium thiosulfate with iodine:
2BaS2O3 + I2 ? BaS4O6 + BaI2
The tetrathionate is insoluble in ethanol and addition serves to cause precipitation. If this is done slowly, crystals of the dihydrate appear. This salt was first isolated by Fordos and Ge¨lis in 1842. In another method, the chloride is reacted with ammonium tetrathionate:
BaCl2+ (NH4)2S2O6 ? BaS4O6+ 2NH4Cl
The tetrathionate can be crystallized from solution by slow evaporation and the addition of alcohol. The crystals of this salt are prismatic and monoclinic with cell parameters of a=5.17? , b=9.46? , c=19.07?, β=96°. There are four molecules per unit cell. The sulfur chain of the tetrathionate anion is unbranched and nonplanar. Three oxygen atoms are arranged in approximately tetrahedral positions around each of the terminal sulfur atoms, at an average distance of 1.41? , the length of the sulfur–sulfur bond is 2.02? and that of the terminal S to S bonds is 2.12? , the bond angle between the two divalent sulfur atoms is 103 and the dihedral angle is 90°. The space group is C2h⁵ – P2¹/c.