Potassium ferricyanide is an inorganic substance, chemical formula Kthree[Fe(CN)six], commonly known as hematite and potassium hematite, with a molecular weight of 329.24, it is a red crystal, soluble in water, and the aqueous solution has yellow green fluorescence, and contains ferricyanide complex ion [Fe (CN)six]3−。
Potassium ferricyanide was prepared by German chemistsLeopold GamelinDiscovered in 1822, German chemistRobert Wilhelm Bunsen The composition and crystallization of potassium ferricyanide were successfully determined in 1846.It is mainly used in photographic paper, pigment, leather making, printing, pharmacy, fertilizer, mordant, electroplating, paper making, steel and other industries.The central atom of the substance isIron ion（Fe3+），LigandsIt is cyanide ion (CN-），coordination number6,Inner boundIs ferricyanide ion {[Fe (CN)six]3-}, the outside is potassium ion (K+）。
Solubility (water): 36 g/100 mL (cold water), 77.5 g/100 mL (hot water).[1]Its aqueous solution gradually decomposes during storage.It is unstable when exposed to sunlight or dissolved in water, and can be decomposed by acid.Encounter Fe2+Dark blue precipitate is generated.
chemical property
stability: The aqueous solution is easy to decompose under the action of light and alkali.meetFerrous saltDark blue precipitate is generated.It can be completely decomposed after burning.It can be decomposed by acid and reduced toPotassium ferrocyanide。It can be completely decomposed after burning, producing high toxicityPotassium cyanideandCyanogen。However, at room temperature, solid potassium hematite is very stable.Its aqueous solution is easy to decompose under the action of light and alkali, and will generate dark blue precipitate in case of ferrous salt（Teng's blue）。
See photo decomposition:
Combustion decomposition:
Generate precipitation when encountering ferrous salt:
Potassium ferricyanide can react with various salts and may precipitate metal salts. The test list (potassium ferricyanide is 0.1mol/L) is as follows:
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Group I
CuSOfour
Dark yellowish brown sediment
AgNOthree
Orange precipitate
Hg(NOthree)two
Light yellowish brown sediment
BaCltwo
No obvious phenomenon
ZnSOfour
Light orange precipitate
Pb(NOthree)two
No obvious phenomenon
FeClthree
Greenish brown precipitate
Altwo(SOfour)three
No obvious phenomenon
CoCltwo
Brick red sediment
MnSOfour
Dark yellowish brown sediment
Group II
SnClfour
Bright yellow sediment
CdSOfour
Yellow precipitate
MgCltwo
No obvious phenomenon
Ni(NOthree)two
Orange yellow precipitate
SbClthree
Bright yellow sediment
NathreeCo(NOtwo)six
Yellow precipitate
Bi(NOthree)two
Yellowish sediment
SnCltwo
(acidification)
Bright yellow sediment
Existing FeSOfour
(acidification)
Dark blue solution is generated, and the supernatant is slightly green after standing
Hgtwo(NOthree)two
(acidification)
Yellowish sediment
Potassium ferricyanide will decompose into highly toxic hydrocyanic acid when exposed to ultraviolet light or sunlight, or in acidic medium (such as 20% sulfuric acid) and heated.
The reaction takes place in neutral environment, K=1/(Ksp * Kstable)=9.55 e-6 (different reactions are coupled in acid neutralization and alkali to increase K)[2]
toxicology data
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Acute toxicity: oral LD in ratsfifty：2970 mg/kg；Mouse oral LCfifty：1600 mg/kg；
Main irritant effects: on the skin: may cause inflammation;Above the eyes: may cause inflammation;No known sensitization effects.
Calculate chemical data
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1. Drainage parameter calculation reference value (XlogP): 0
2. Number of hydrogen bond donors: 0
3. Number of hydrogen bond receptors: 12
4. Number of rotatable chemical bonds: 0
5. Number of tautomers: 0
6. Topological molecular polar surface area: 143
7. Number of heavy atoms: 16
8. Surface charge: 0
9. Complexity: 127
10. Number of isotope atoms: 0
11. Determine the number of atomic structure centers: 0
12. Number of uncertain atomic structure centers: 0
13. Determine the number of chemical bond structural centers: 0
14. Number of indeterminate chemical bond structure centers: 0
15. Number of covalent bond units: 10
Preparation method
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Chlorine oxidation method
It is made from potassium xanthate as raw material by chlorine oxidation method, or by electrolytic method through oxidation-reduction reaction of potassium xanthate.Chlorine oxidation method The hot solution of potassium xanthate is oxidized to produce potassium hematite at about 60~65 ℃ under the action of chlorine.When the pH value of the reaction feed solution is controlled to be 6-7, stop feeding chlorine gas, then add potassium permanganate saturated solution, and use ammonium ferrate sulfate to test until it is brownish red.Adjust the acidity and alkalinity of the material with hydrochloric acid to make the pH value between 7 and 8. After reaction, the material is settled, filtered, and evaporated in vacuum until the relative density of the solution is 12, and then cooled, crystallized, centrifuged, and dried to obtain the finished product of potassium hematite.
Electrolyte the saturated solution of potassium xanthate below 60 ℃ to make potassium xanthate undergo self coupling oxidation-reduction reaction to produce potassium hematite and by-productsPotassium hydroxide。When the content of potassium ferricyanide in the electrolyte reaches 320g/L, it starts to cool and crystallize. When the concentration drops to 280g/L, it is separated and dried to obtain the finished product of potassium hematite.
Add industrial potassium ferricyanide into water (add 130~135 g to 350 mL water), stir, heat (not more than 70 ℃), filter, cool, crystallize, centrifuge, dry, wash with a small amount of water, and dry at room temperature to obtain analytical pure product.
application area
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bleaching agents
Bleach for silver halide color photographic materials, thinner for black and white photographic materials, and bleach for browning black and white photographs.The widely used high-temperature rapid color washing process is no longer used.However, the development of color film is still widely used.Potassium ferricyanide bleaching solution is used to wash the color background, which is composed of potassium ferricyanide and potassium bromide. It is characterized by fast bleaching speed but low stability. The color developer entrained in the solution with high concentration will produce fog that affects the quality, and may generate highly toxic substances such as hydrocyanic acid and potassium cyanide.[3]
Corrosive
Potassium ferricyanide mixed with sodium hydroxide and water can be used as alloy etchant to corrode high chromium cast iron or show that ζ phase in stainless steel is equal to that in ferritic austenitic stainless steel.[4]Or as a method to display the microstructure of duplex stainless steel carbon steel composite plate, first use potassium ferricyanide, potassium hydroxide and residual water mixture to show the microstructure of duplex steel, wash it with running water, spray anhydrous ethanol, dry it quickly, and then use 4% nitric acid alcohol solution by volume to corrode the microstructure of carbon steel or low-alloy steel, wash it with running water, spray anhydrous ethanol,Rapid drying.
Reagents for analysis
Spot analysis is used to determine the content of high iron, cesium, gallium, mercury, zinc, uranium dioxide or chromium in passivation solution.Sulfur content analysis of methanol in nitrogen fertilizer production.Analysis of wastewater from the production of herbicide.For example, the color developing agent of thin-layer chromatographic analysis system is potassium ferricyanide ferric chloride reagent;[5]The rapid electrochemical detection of hydrogen sulfide based on screen printed electrode using potassium ferricyanide solution as electronic mediator, and the voltammetric response of hydrogen sulfide on screen printed electrode were studied by cyclic voltammetry and differential pulse voltammetry.[6]
Blueprint printing
Teng's blue formed from potassium ferricyanide is used in the Carlo method for blueprint printing and photographythree[Fe(CN)six]And ferrous ion.[7]
Mild oxidant
It can be used as a mild oxidant.Determination of serum total bilirubin if used as oxidant[8]Determination of trace lead and mercury by hydride generation atomic fluorescence spectrometry.[9]The polyaniline spiny microspheres with good water solubility and large specific surface area were prepared by chemical oxidation using potassium ferricyanide as oxidant and coordination compound potassium ferricyanide as oxidant.[10]
indicator
Oscillographic polarographic titration with potassium ferricyanide as titrant is called potassium ferricyanide titration, that is, Kthree[Fe(CN)six]Based on the oxidation-reduction reaction of substances in hydrochloric acid medium, Kthree[Fe(CN)six]Titrate the substance with standard solution to Kthree[Fe(CN)six]The appearance of notch on oscillopolarography is used to indicate the titration end point.[11]As a titrant, potassium ferricyanide solution has many advantages, such as high purity of potassium ferricyanide, stable aqueous solution, weak oxidant, and selective oxidation performance that strong oxidants do not have.[12]
Histologically, Kthree[Fe(CN)six]To detect ferrous ions in biological tissues and react with ferrous ions in acidic solution to produce insoluble blue pigment, which is calledTeng's blue。testingIron ionIs used whenPotassium ferrocyanide, also generates insoluble blue pigment, calledprussian blue 。 The research shows that Teng's blue and Prussian blue are the same substance, and the slightly different color is caused by different preparation methods.[13]
Potassium ferricyanide andPhenolphthaleinMixedRust indicator。useColorimeterAnalyze dark blue Fefour[Fe(CN)six]threeThe initial number of moles of iron ion can be calculated.[13]
Test of ferrous ion: take a small amount of sample in the test tube and drop potassium ferricyanide solution. If blue precipitate (ferrous ferricyanide) is produced, it indicates the existence of ferrous ion.[14]
Safety measures
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Environmental hazards
It is harmful to the environment and can cause pollution to water bodies.
Health hazards
Health hazard: It may be harmful to the body if inhaled, ingested or absorbed through the skin.May cause kidney damage.Hydrogen cyanide can be produced by heating or acid.
Some people think that potassium ferricyanide is non-toxic.Because in this coordination compound, iron ion and highly toxic cyanogen combine to form a solid ferrocyanide, which will not decompose in aqueous solution.Only under the condition of high temperature burning can the decomposition occur to generate highly toxic cyanide.
Hazard prevention
First aid measures
Skin contact: Take off contaminated clothes and wash with flowing water.
Eye contact: Lift the eyelid and flush with flowing water or physiological saline.Get medical attention.
Inhalation: leave the site to fresh air.If breathing is difficult, give oxygen.Get medical attention.
Ingestion: drink enough warm water to induce vomiting.Gastric lavage and catharsis.Get medical attention.[15]
Fire fighting measures
Hazard characteristics: It is subject to high thermal decomposition and emits corrosive and irritating smoke.
Extinguishing method: firefighters must wear full body fire and gas protective clothing and extinguish the fire upwind.When putting out a fire, try to move the container from the fire site to an open place.[15]
Leakage emergency treatment
Isolate the leakage contaminated area and restrict access.It is recommended that emergency personnel wear dust masks (full face masks) and gas suits.Flush with a large amount of water, and put the diluted washing water into the waste water system.In case of large leakage, collect and recycle or transport to waste disposal site for disposal.[15]
Storage method
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Store in a cool and ventilated warehouse.Keep away from kindling and heat sources.Keep container sealed.It shall be stored separately from oxidants and acids, and mixed storage is strictly prohibited.The storage area shall be equipped with appropriate materials to contain leakage.[15]
