Potassium ferrocyanide

 

Potassium ferrocyanide

Chemical formula	K4(Fe(CN)6)
OTP appearance	yellow crystals
Molar Mass(g/mol)	368
Melting Point(°C)	decomp
Density(g/cc)	1.85
Solubility in water(g/L)	289
Solubility in ethanol(g/L)	insoluble
NFPA 704	0 1 0

Uses

Other

• Precursor to Prussian blue on WHO LEM
• Production is a relatively safe sink for cyanides

Natural occurrence

• does not occur in nature

Hazards

• "nontoxic"
• Do not heat or acidify, these actions may produce free cyanides.

Production

Synthesis

via nitrogenous biomass

This general process is repeated in many texts including Industrial Chemistry and Manual of Chemical Technology

1. Melt 100ubm potassium carbonate in a container devoid of oxygen
2. Add 75-400ubm of nitrogenous biomass (feathers, horn, skins, leather, dry blood) directly to the melt

   N.B.: Production of solvated potassium cyanide and potassium sulfate KCN,K₂SO₄

3. Allow to cool
4. Mix with water
5. Filter
6. Recycle residue (or dispose of carefully, it may be toxic)
7. Retain filtrate (it contains potassium cyanide, which is very poisonous/toxic)
8. Add 10 ubm iron filings to a basic solution

   6 KCN + Fe + 2 H₂O

   {OH-

   →

   }

   K₄(Fe(CN)₆) + 2 KOH + H₂

via hydrogen cyanide

1. Combine iron (II) chloride and calcium hydroxide in water
2. Bubble hydrogen cyanide through the mixture

   2 FeCl₂(OH)₂(H₂O)₂ + 4 Ca(OH)₂ + 12 HCN → 2 Ca₂[Fe(CN)₆] + 14 H₂O + 4 HCl + O₂

3. Combine with 2 molar equivalents of potassium chloride, precipitating the calcium/sodium salt

   Ca₂[Fe(CN)₆] + 2 KCl → CaK₂[Fe(CN)₆(s)] + CaCl₂

4. Combine with potassium carbonate

   CaK₂[Fe(CN)₆](aq) + K₂CO₃(aq) → K₄[Fe(CN)₆](aq) + CaCO₃(s)

5. Filter
6. Discard residue (calcium carbonate)
7. Evaporate filtrate leaving potassium ferrocyanide