POTASSIUM THIOCYANATE (KSCN): STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2024

The potassium thiocyanate is an inorganic compound consisting of the elements potassium (K), sulfur (S), carbon (C) and nitrogen (N). Its chemical formula is KSCN. It is a colorless or white solid very soluble in water. It is made up of a K ⁺ potassium ion and a SCN ^- thiocyanate ion. KSCN is found in saliva in abundance.

Potassium thiocyanate is used as a laboratory reagent for various types of chemical analysis. It is also used in inks and paints.

Solid KSCN Potassium Thiocyanate. O.Luci / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

KSCN has been used to dissolve dentin gelatin (material under the enamel of teeth) before applying the material or resin that repairs teeth. It is also used in research on vaccines, since it allows the extraction of certain biochemical elements from bacteria.

It is used in the form of a solution where metals dissolve during the polishing process by electricity or electropolishing. It has also been used in obtaining fake blood for movies and plays.

It is sometimes misused to increase the stability of milk when it is not kept refrigerated. But it has the downside of causing hypothyroidism, a disease in which the thyroid gland malfunctions.

Structure

Potassium thiocyanate is made up of a K ⁺ potassium cation and a NCS ^- thiocyanate anion. The latter is formed by a nitrogen (N) linked to a carbon (C) through a triple bond and a sulfur (S) attached to carbon through a single bond.

Chemical structure of KSCN potassium thiocyanate. Edgar181 / Public domain. Source: Wikimedia Commons.

Nomenclature

• Potassium thiocyanate
• Potassium sulfocyanate
• Potassium salt of thiocyanic acid
• Potassium rhodanate
• Potassium rhodanide

Properties

Physical state

Colorless or white solid.

Molecular weight

97.18 g / mol

Melting point

173 ºC

Decomposition temperature

500 ºC

Density

1.88 g / cm ³

Solubility

Very soluble in water: 217 g / 100 mL at 20 ° C, 238 g / 100 mL at 25 ° C. Soluble in ethanol.

pH

A 5% solution of KSCN has a pH between 5.3 and 8.7.

Other properties

Pure, dry potassium thiocyanate samples are stable indefinitely when kept in the dark in tightly covered glass jars. However, in contact with direct sunlight the colorless crystals quickly turn yellowish.

Solutions of pure KSCN salt protected from light are completely stable.

KSCN is capable of swelling gelatin and collagen. The aqueous solutions of potassium thiocyanate when reacting with manganese dioxide MnO ₂ oxidize and form thiocyanogen (SCN) ₂.

Obtaining

Potassium thiocyanate can be prepared by melting potassium cyanide (KCN) with sulfur (S). The reaction is fast and quantitative.

KCN + S → KSCN

It can be obtained in solution by dissolving sulfur (S) in benzene or acetone and adding a solution of potassium cyanide (KCN) in isopropanol. This reaction is used to analyze the amount of sulfur in a solution.

Potassium thiocyanate can be obtained pure by successive recrystallizations from water or ethanol.

Presence in nature

Potassium thiocyanate is found in saliva abundantly (15 mg / dL), but it is absent in the blood.

Also the milk of some mammals (such as cows) has very small amounts of thiocyanate naturally.

Applications

In various applications

Potassium thiocyanate has been used in various chemical analyzes. It has been used for the analysis or titration of silver ion, also as a reagent and indicator for other analyzes.

KSCN is used in colorants and pigments. It is used in paints and inks.

In the photography industry it is used especially in the manufacture of photographic film, as it serves to allow the firm deposition of gelatin from plastic films.

The concentration of thiocyanate in the blood has been used in medical-scientific experiments to determine the degree to which some people smoke, since thiocyanate is a product derived from hydrogen cyanide (HCN) present in tobacco smoke.

In dental applications

Potassium thiocyanate has been used in the repair of animal teeth. It has been successfully applied to the dentin surface as a pretreatment prior to applying the agent to fill or plug the open hole.

Dentin is the layer that is found under the enamel of the teeth.

The KSCN has been used to treat the dentin surface of the teeth before applying the material that fills the cavities. Author: Mudassar Iqbal. Source: Pixabay.

Potassium thiocyanate favors the swelling of the gelatin that is on the dentin, so this layer is easily removed and a better adhesion or bonding of the material that closes the tooth (resin) results.

In medical science laboratories

KSCN is used in the preparation of vaccines or bacterial extracts.

The pathogenic bacteria are grown by incubation in suitable laboratory containers. A phosphate buffer and KSCN are then added to the container where the bacteria culture is located.

Bacterial cultures are extracted with KSCN to obtain vaccines for medicoscientific experiences. Author: WikiImages. Source: Pixabay.

A portion of this bacterial preparation is taken and placed in a jar. It is stirred for a suitable time and the suspension is centrifuged to separate the liquid from the solid material. The supernatant (liquid) is collected and dialyzed.

The result is an extract that is used to vaccinate in scientific experiments with laboratory animals.

In the metals industry

Potassium thiocyanate is used in the electropolishing of metals. Electropolishing is a chemical process that allows to treat the surface of a metal to reduce its micro-roughness, that is, to smooth the metal surface.

This is done with electricity, causing the metal to be smoothed to act as the positive pole or anode of the electrolytic cell. The roughness dissolves in the potassium thiocyanate solution and the metal is thus smoother.

On the set of movies or in the theater

The KSCN is used in the simulation of blood in film and television films or in plays.

For example, a solution of potassium thiocyanate (KSCN) is applied to the area of ​​the body that will "suffer" the cut or simulated assault. The plastic knife or sharp object simulation is bathed in a solution of ferric chloride (FeCl ₃).

The "sharp" object having FeCl ₃ is gently passed over the skin moistened in KSCN. Immediately, a red streak or stain will form, very similar to blood.

The KSCN has been used to obtain fake blood in movies or theater. Author: Corey Ryan Hanson. Source: Pixabay.

This is due to the formation of a complex of ferric thiocyanate and water ²⁺ which is of an intense red color very similar to blood:

KSCN + FeCl ₃ + 5 H ₂ O → ²⁺ + 2 Cl ^- + KCl

KSCN potassium thiocyanate mixed with ferric chloride in water forms a deep red compound similar to blood. Author: Clker-Free-Vector-Images. Source: Pixabay.

Potassium thiocyanate misuse

Potassium thiocyanate is used unscrupulously to prevent milk from being attacked by bacteria or fungi, losing its properties and deteriorating.

In tropical countries a method called "lacto-peroxidase system" or LP system is used, which increases the stability of milk when stored at high ambient temperatures, when its refrigeration is not possible.

In some countries it is not possible to refrigerate the milk and therefore potassium thiocyanate is used to prevent it from deteriorating. Author: Thomas B. Source: Pixabay.

This method uses the natural antibacterial system of milk, which is activated by increasing the concentration of thiocyanate (already present in small amounts in milk) and hydrogen peroxide (H ₂ O ₂).

However, this method is not allowed in many countries by the authorities that regulate processed foods.

Some unscrupulous people add KSCN to milk in an irrational way with or without H ₂ O ₂, which constitutes a danger to the health of the consumer, since thiocyanates are substances that cause damage to the thyroid and can cause hypothyroidism when ingested in high concentrations.

Milk with excess potassium thiocyanate can harm the health of those who eat it. Author: Tookapic. Source: Pixabay.

Risks

Inhaling potassium thiocyanate powder should be avoided. It is advisable to wear gloves and protective glasses when handling it. After brief exposure to potassium thiocyanate it can cause effects on the nervous system, such as excessive emotion without motive, agitation and seizures.

After a long exposure, the thyroid and the central nervous system can be affected, which manifests as hypothyroidism and deterioration of some functions respectively. When ingested it can cause confusion, nausea, vomiting, seizures, and weakness.

Igniting or burning KSCN releases highly poisonous cyanide gases; this also happens when adding acids. In the laboratory, it must be handled inside a well-ventilated fume hood.

References

1. Jarvinen, LZ et al. (1998). Induction of Protective Immunity in Rabbits by Coadministration of Inactivated Pasteurella multocida Toxin and Potassium Thiocyanate Extract. Infection and Immunity, Aug, 1998, p. 3788-3795. Recovered from ncbi.nlm.nih.gov.
2. Tani, Y. and Togaya, T. (1995). Dentin Surface Treatment without Acids. Dental Materials Journal 14 (1): 58-69, 1995. Retrieved from jstage.jst.go.jp.
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4. Balmasov, AV et al. (2005). Electropolishing of Silver in Water-Organic Solutions of Potassium Thiocyanate. Prot Met 41, 354-357 (2005). Recovered from link.springer.com.
5. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
6. Lide, DR (editor) (2003). CRC Handbook of Chemistry and Physics. 85 ^th CRC Press.
7. Tyner, T. and Francis, J. (2017). Potassium Thiocyanate. ACS Reagent Chemicals. Recovered from pubs.acs.org.
8. Kanthale, P. et al. (2015). Qualitative test for the detection of extraneous thiocyanate in milk. J Food Sci Technol (March 2015) 52 (3): 1698-1704. Recovered from ncbi.nlm.nih.gov.
9. Roy, D. et al. (2018) Silicon Quantum Dot-Based Fluorescent Probe: Synthesis Characterization and Recognition of Thiocyanate in Human Blood. ACS Omega 2018, 3, 7, 7613-7620. Recovered from pubs.acs.org.
10. Gammon, K. (2018). The Science of Fake Blood. Inside Science. Recovered from insidescience.org.