Sodium ferrocyanide is the sodium

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

of the coordination compound of formula e(CN)₆sup>4−. In its

hydrous In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...

form, Na₄Fe(CN)₆ (

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

ferrocyanide Ferrocyanide is the name of the anion CN)6">cyanide.html" ;"title="e(cyanide">CN)6sup>4−. Salts of this coordination complex give yellow solutions. It is usually available as the salt potassium ferrocyanide, which has the formula K4Fe(CN)6. e ...

decahydrate), it is sometimes known as yellow prussiate of soda. It is a yellow

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

line solid that is soluble in water and insoluble in alcohol. The yellow color is the color of ferrocyanide

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

. Despite the presence of the

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...

s, sodium ferrocyanide has low

toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

(acceptable daily intake 0–0.025 mg/kg body weight). The

s are less toxic than many salts of cyanide, because they tend not to release free cyanide. However, like all ferrocyanide salt solutions, addition of an acid can result in the production of hydrogen cyanide gas, which is extremely toxic.

Uses

When combined with an Fe(III) salt, it converts to a deep blue pigment called

Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue or, in painting, Parisian or Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula Fe CN)">Cyanide.html" ;"title="e(Cyani ...

, Fe CN).html"_;"title="Cyanide.html"_;"title="e(Cyanide">CN)">Cyanide.html"_;"title="e(Cyanide">CN)_It_is_used_as_a_stabilizer_for_the_coating_on_welding.html" ;"title="Cyanide">CN).html" ;"title="Cyanide.html" ;"title="e(Cyanide">CN)">Cyanide.html" ;"title="e(Cyanide">CN) It is used as a stabilizer for the coating on welding">Cyanide">CN).html" ;"title="Cyanide.html" ;"title="e(Cyanide">CN)">Cyanide.html" ;"title="e(Cyanide">CN) It is used as a stabilizer for the coating on welding rods. In the petroleum industry, it is used for removal of mercaptans. In the EU, ferrocyanides (E 535–538) were, as of 2018, solely authorized as additives in table salt, salt and salt substitutes, where they serve as anticaking agents. The

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

s are the organ susceptible to ferrocyanide

, but according to the

EFSA The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...

, ferrocyanides are of no safety concern at the levels at which they are used.

Production

Sodium ferrocyanide is produced industrially from hydrogen cyanide,

ferrous chloride Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as ...

, and calcium hydroxide, the combination of which affords Ca₂ e(CN)₆ A solution of this salt is then treated with sodium salts to precipitate the mixed calcium-sodium salt CaNa₂ e(CN)₆sub>2, which in turn is treated with sodium carbonate to give the tetrasodium salt.

References

{{Sodium compounds Sodium compounds Cyano complexes E-number additives Nephrotoxins