The Sodium tetrathionate is prepared from the thiosulphate either by the action of iodine or by oxidation with cupric chloride. It can be precipitated from solution by addition of alcohol. With sodium carbonate it yields sodium thiosulphate:
4Na2S4O6+5Na2CO3 = 7Na2S2O3+2Na2SO4+5CO2.
The heat of formation in aqueous solution is given by Berthelot as 387.2 Cal. A dihydrate exists, its heat of solution being –9.5 Cal.
The tetrathionate is converted by the action of sodium sulphite into trithionate and thiosulphate:
Na2S4O6+Na2SO3=Na2S3O6+Na2S2O3.
With alkali-metal cyanides the tetrathionate reacts in accordance with the equation
Na2S4O6+3NaCN+H2O = NaCNS+Na2SO4+Na2S2O3+2HCN.
At the boiling-point, in presence of excess of cyanide, the thiosulphate formed reacts further to produce thiocyanate and sulphite. |