Potassium ferro-heptanitroso sulphide

Potassium ferri-disulphite, K3Fe(S03)2S04, results when a solution of potassium ferro-heptanitroso sulphide is digested at 4° C. with sodium hydrogen sulphite for about a month. It yields lustrous, dark yellow leaflets which are practically insoluble in cold water, but in boiling water are decomposed, yielding ferric hydroxide and a soluble ferric salt. 

Potassium ferro-heptanitroso sulphide, KFe4(N0)7S3.H20.—To prepare this salt, Pavel 4 raised a solution of potassium nitrite to boiling, added sodium sulphide, and, finally, with repeated shaking, a solution of ferrous sulphate in small quantities at a time. Upon crystallisation the nitroso derivative separated out m monoclinic crystals which were purified by recrystallisation from warm water and carbon disulphide in succession, and finally dried over phosphorus pentoxide. 

When a solution of potassium ferro-dinitroso thiosulphate, KFe(N0)2S203.H20, is boiled, sulphur dioxide is expelled, and ferric hydroxide precipitated. Upon concentrating the clear solution obtained by filtering, crystals of potassium ferro-heptanitroso sulphide are obtained.5... 

On boiling potassium ferro-heptanitroso sulphide with dilute potassium hydroxide, ferric hydroxide is deposited, and, upon concentration of the filtered liquid, dark red crystals of potassium ferro-dinitroso sulphide4 are obtained, to which the formula KFe(N0)2S.2H20 is ascribed. The reaction may be represented as follows —... 

Sodium ferri-disulphite, Na3Fe(S03)2S04.6H20, may be prepared by digesting a solution of sodium ferro-heptanitroso sulphide with sodium hydrogen sulphite for several days. It crystallises in flat, yellow prisms, and closely resembles the corresponding potassium salt. 

When acted upon with dilute sulphuric acid, the potassium salt yields the free acid, hydrogen ferro-heptanitroso sulphide,KFe4(NO)7S3, as an insoluble, amorphous precipitate. It is very unstable. When boiled with dilute potassium hydroxide solution, the potassium hepta-nitroso derivative yields potassium ferro-dinitroso sulphide, KFe(NO)2S. 2H20 (see p. 181). 

Sodium ferro-heptanitroso sulphide, NaFe4(NO)7S3.2H20, may be obtained in a similar manner to the potassium salt by boiling a solution of sodium ferro-dinitroso thiosulphate, as also by the action of sodium nitrite and sulphide solutions upon ferrous sulphate. In this latter reaction the sodium sulphide may be replaced by sodium thiocarbonate, Na2CS3. 

The sodium salt,1 NaFe(N0)2S203.2H20, is obtained in a similar manner to the preceding salt. It yields either laminated or needle-shaped crystals, which are glistening black in appearance. They are appreciably more soluble in water than those of the potassium salt, and yield a deep brown solution. The salt is fairly stable below 0° C., but above that temperature continuously evolves nitric oxide. When its aqueous solution is boiled, sulphur dioxide is expelled and ferric hydroxide precipitated. Upon concentrating the clear solution obtained by filtering, crystals of sodium ferro-heptanitroso sulphide, NaFe4(N0)7S3.H20, separate out.2... 

Of these the first-named is readily obtained by adding a solution of caesium chloride to one of sodium heptanitroso ferro-sulphide, when the caesium derivative is precipitated as an insoluble black crystalline powder. The rubidium derivative, obtained in an analogous manner, presents a similar appearance. The thallium salt is likewise difficultly soluble in water, and is obtained by double decomposition with thallium sulphate and the potassium derivative. 

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