por What is chromium chloride?
He chromium chloride (CrCl3) It is an inorganic salt composed of Cr3+ cations and Cl– anions in a 1:3 ratio, that is, for every Cr3+ there are three Cl–. As will be seen later, their interactions are not ionic. This salt can occur in two forms: anhydrous and hexahydrate.
The anhydrous form is characterized by a violet-reddish coloration, while the hexahydrate, CrCl3.6H2O, is dark green. The incorporation of water molecules modifies the physical properties of these crystals, such as their boiling and melting points, densities, etc.
Chromium(III) chloride (according to stock nomenclature) decomposes at high temperatures, transforming into chromium(II) chloride, CrCl2. It is corrosive to metals, although it is used in chrome plating, a process in which metals are coated with a thin layer of chrome.
Cr3+, from its respective chloride, has been used in the treatment of diabetes, especially in patients receiving total parenteral nutrition (TPN), who do not ingest the required amount of chromium. However, the results are much better (and more reliable) if it is supplied as a picolinate.
Chromium Chloride Structure
CrCl3 despite being a salt, the nature of its interactions are not purely ionic, they have a certain covalent character, product of the coordinations between Cr3+ and Cl–, which give rise to a deformed octahedron (upper image). Chromium is located in the center of the octahedron, and chlorines in its vertices.
The CrCl6 octahedron may, at first glance, contradict the CrCl3 formula, however, this complete octahedron does not define the unit cell of the crystal, but rather a cube (also deformed), which cuts the green spheres or chlorine anions in half.
Anhydrous Crystalline Coatings
Thus, the unit cell with this octahedron maintains the ratio 1:3. Reproducing these deformed cubes in space, the CrCl3 crystal is obtained, which is represented in the image below with a three-dimensional filling model, and a spheres and bars model.
This crystalline layer is one of the many that make up the scaly violet-reddish crystals of CrCl3 (do not confuse the true color of the crystal with that of the green spheres).
As can be seen, the Cl– anions occupy the surface, so their negative charges repel the other crystalline layers. Consequently, the crystals become flaky and brittle, but shiny, because of the chromium.
If these same layers are viewed from a side perspective, distorted tetrahedrons will be observed instead of octahedrons:
Here it is further facilitated to understand why the layers repel each other when Cl– anions on their surfaces bind.
Properties
Names: cchromium(III) chloride, chromium(III) trichloride, chromium(III) chloride anhydrous.
Chemical formula: CrCl3 (anhydrous). CrCl3.6H2O (hexahydrate).
Molecular weight: 158.36 g/mol (anhydrous). 266.43 g/mol (hexahydrate).
Physical description: yesreddish-violet solids and crystals (anhydrous). Dark green crystalline powder (hexahydrate, bottom image). In this hydrate it can be seen how water inhibits the shine, a metallic characteristic of chrome.
Melting point: 1,152 °C (2,106 °F, 1,425 K) (anhydrous). 83 °C (hexahydrate).
Boiling point: 1300 °C (2,370 °F, 1,570) (anhydrous).
Water solubility: slightly soluble (anhydrous). 585 g/L (hexahydrate).
Solubility in organic solvents:ssoluble in ethanol, but insoluble in ether (anhydrous).
Density: 2.87 g/cm3 (anhydrous). 2.76 g/cm3 (hexahydrate).
Storage temperature: <30°C
Decomposition: cWhen heated to decomposition, chromium(III) chloride emits toxic fumes of chlorine-containing compounds. These compounds are also released when chromium(III) chloride comes into contact with strong acids.
Corrosion: andIt’s highly corrosive and can attack certain steels.
Reactions: andIt’s incompatible with strong oxidizers. It also reacts strongly with lithium and nitrogen. When heated in the presence of hydrogen, it is reduced to chromium(II) chloride, with the formation of hydrogen chloride.
2 CrCl3 + H2 => 2 CrCl2 + 2 HCl
pH: andn an aqueous solution, and with a concentration of 0.2 M: 2.4.
Synthesis
Chromium(III) chloride hexahydrate is produced by reacting chromium hydroxide with hydrochloric acid and water.
Cr(OH)3 + 3 HCl + 3 H2O => CrCl3.6H2O
Then, to obtain the anhydrous salt, we proceed to heat the CrCl3.6H2O in the presence of thionyl chloride, SOCl2, hydrochloric acid, and heat:
[Cr(H2O)6]Cl3 + 6SOCl2 + ∆ → CrCl3 + 12 HCl + 6SO2
Alternatively, CrCl3 is obtained by passing chlorine gas over a mixture of chromium oxide and carbon.
Cr2O3 + 3 C + Cl2 => 2 CrCl3 + 3 CO
And finally, being the most used method, is to heat your oxide with a halogenating agent, such as carbon tetrachloride:
Cr2O3 + 3CCl4 + ∆ → 2CrCl3 + 3COCl2
Applications
industrial
Chromium chloride is involved in the preparation on site of chromium (II) chloride, a reagent involved in the reduction of alkyl halides, and in the synthesis of (E)-alkenyl halides.
It is used in the chrome plating technique. This consists of depositing, through electroplating, a thin layer of chrome on metal objects or other material with a decorative objective, thus increasing the resistance to corrosion and also the surface hardness.
It is used as a textile mordant, serving as a link between the dyeing material and the fabrics to be dyed. In addition, it is used as a catalyst for the production of olefins and waterproofing agents.
therapeutic
The use of Chromium Chloride Supplement, USP, is recommended in patients receiving only intravenous solutions, administered for total parenteral nutrition (TPN). Therefore, only when these patients do not receive all their nutritional requirements.
Chromium (III) is part of the glucose tolerance factor, an activator of the reactions that insulin promotes. Chromium(III) is thought to activate glucose, protein, and lipid metabolism, facilitating insulin action in humans and animals.
Chromium is present in numerous foods. But its concentration does not exceed 2 µg per serving, with broccoli being the food with the highest contribution (11 µg). Additionally, the intestinal absorption of chromium is low, with a value of 0.4 to 2.5% of the amount ingested. This makes it difficult to establish a diet to supply chromium. In 1989, The National Academy of Sciences recommended 50 to 200 µg/day as an adequate intake of chromium.
risks
Among the possible risks of consuming this salt as a chromium supplement are:
Strong stomach pains.
Abnormal bleeding, which can range from difficulty healing a wound, redder bruises, or a darkening of stools from internal bleeding.
Irritations in the digestive system, causing ulcers in the stomach or intestines.
Dermatitis.
References
Shiver & Atkins. Inorganic Chemistry (Fourth Edition). Mc Graw Hill.
Chromium(III) chloride. Retrieved from en.wikipedia.org.
Chromium(III) Chloride. Retrieved from alpha.chem.umb.edu.
Chromium chloride hexahydrate. Retrieved from pubchem.ncbi.nlm.nih.gov.
Tomlinson, Carole A. Chromium Chloride Side Effects. Leaf Group Ltd. Recovered from healthfully.com.