PREPARATION OF PRUSSIAN BLUE i.e. Fe4[Fe(CN)6]3

PREPARATION OF PRUSSIAN BLUE ( Fe4[Fe(CN)6]3)

THEORY:

Prussian blue is a dark blue pigment with the formula Fe4[Fe(CN)6]3. Another name for it is Berlin Blue, or sometimes in painting, Parisian Blue. It was one of the first synthetic pigments used by humans. It is employed as a very fine colloidal dispersion, as the compound itself is not

soluble in water. In medicine, Prussian blue is used as an antidote for certain kinds of heavy metal poisoning, e.g., by cesium and thallium. In particular it was used to absorb 137Cs+ from those poisoned in the Goiania accident. Prussian Blue is orally administered. The therapy

exploits Prussian Blue’s ion exchange properties and high affinity for certain “soft” metal cations. Prussian blue is produced by oxidation of ferrous ferrocyanide salts. It contains ferric

hexacyanoferrate(II) in a cubic lattice crystal structure. It is insoluble in water but also tends to form a colloid thus can exist in either colloidal or water-soluble form, and an insoluble form.

Prussian blue is included in the World Health Organization Model List of Essential Medicines as a specific antidote used in poisonings to provide symptomatic and supportive treatment. 

The structure of Prussian blue is shown as:

GLASSWARE AND CHEMICALS REQUIRED:

Glassware and apparatus: Beaker, Buchner funnel, filter flask, tubing, filter-vac rubber rings, conical flask, filter paper.

Reagents and Chemicals: Iron fillings, Potassium Ferrocyanide (K4[Fe(CN)6]), Sulphuric acid.

PROCEDURE:

Take 2-3 g of iron fillings in a 250 mL of conical flask. To this add 50 mL of dilute H2SO4; close

the flask with rubber cork carrying long glass tubing. Heat the solution gently on a low flame for

5-10 minute. Cool it at laboratory temperature and then filter it. Preserve the filtrate and transfer

the precipitate back to the same conical flask. To this add another 25 mL of dilute H2SO4; close the flask with rubber cork carrying long glass tubing. Again, heat the solution gently on a low

flame for 5-10 minute, cool it and then filter it. Mix both the filtrate in a 500 mL beaker and add

saturated solution of K4[Fe(CN)6] (Potassium Ferrocyanide) to it. Heat the resultant solution

until it turns to green and then transfer this green solution in a porcelain dish. Allow the solution

to get oxidized in open air until the green colour changes to blue (usually oxidation in presence

of air for 3-4 hrs). The oxidation process may become fast if 2-3 mL of dil K2Cr2O7 is added in

it. Filter the blue precipitate and wash it with ethanol and dry it. Take its weight and report the

yield.

REACTIONS INVOLVED:

Following reactions are involved in the formation of Prussian blue pigment (Fe4[Fe(CN)6]3).

RESULTS:

(i) Physical state: Solid

(ii) Colour: Blue

(iii) Yield: ……… g

STRUCTURE:

The structure of Prussian blue is shown in given figure. Four Iron (III) ions are surrounded by

three hexacyanoferrate (II) ions.