Iron(III) chloride
Iron(III) chloride is the inorganic compound with the formula FeCl3. Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The color depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red.
![]() Iron(III) chloride (hydrate) | |||
![]() Iron(III) chloride (anhydrous) | |||
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Names | |||
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IUPAC names
Iron(III) chloride Iron trichloride | |||
Other names
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Identifiers | |||
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3D model (JSmol) |
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard | 100.028.846 | ||
EC Number |
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PubChem CID |
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RTECS number |
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UNII |
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UN number |
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CompTox Dashboard (EPA) |
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InChI
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SMILES
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Properties | |||
FeCl3 | |||
Molar mass |
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Appearance | Green-black by reflected light; purple-red by transmitted light; yellow solid as hexahydrate; brown as aqueous solution | ||
Odor | Slight HCl | ||
Density |
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Melting point | 307.6 °C (585.7 °F; 580.8 K) (anhydrous) 37 °C (99 °F; 310 K) (hexahydrate)[1] | ||
Boiling point |
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Solubility in water |
912 g/L (anhydrous or hexahydrate, 25 °C)[1] | ||
Solubility in |
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+13,450·10−6 cm3/mol[2] | |||
Viscosity | 12 cP (40% solution) | ||
Structure | |||
Hexagonal, hR24 | |||
Space group |
R3, No. 148[3] | ||
Lattice constant |
a = 0.6065 nm, b = 0.6065 nm, c = 1.742 nm α = 90°, β = 90°, γ = 120° | ||
Formula units (Z) |
6 | ||
Coordination geometry |
Octahedral | ||
Hazards[4][5][Note 1] | |||
GHS labelling: | |||
Pictograms |
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Signal word |
Danger | ||
Hazard statements |
H290, H302, H314 | ||
Precautionary statements |
P234, P260, P264, P270, P273, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P390, P405, P406, P501 | ||
NFPA 704 (fire diamond) | |||
Flash point | Non-flammable | ||
NIOSH (US health exposure limits): | |||
REL (Recommended) |
TWA 1 mg/m3[7] | ||
Safety data sheet (SDS) | ICSC | ||
Related compounds | |||
Other anions |
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Other cations |
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Related coagulants |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references |
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Structure and properties
Anhydrous
Anhydrous iron(III) chloride has the BiI3 structure, with octahedral Fe(III) centers interconnected by two-coordinate chloride ligands.[3]
Iron(III) chloride has a relatively low melting point and boils at around 315 °C. The vapor consists of the dimer Fe2Cl6 (like aluminium chloride) which increasingly dissociates into the monomeric FeCl3 (with D3h point group molecular symmetry) at higher temperature, in competition with its reversible decomposition to give iron(II) chloride and chlorine gas.[8]
Hydrates
In addition to the anhydrous material, ferric chloride forms four hydrates. All forms of iron(III) chloride feature two or more chlorides as ligands, and three hydrates feature [FeCl4]−.[9]
- dihydrate: FeCl3·2H2O has the structural formula trans-[FeCl2(H2O)4][FeCl4].
- FeCl3·2.5H2O has the structural formula cis-[FeCl2(H2O)4][FeCl4]·H2O.
- FeCl3·3.5H2O has the structural formula cis-[FeCl2(H2O)4][FeCl4]·3H2O.
- hexahydrate: FeCl3·6H2O has the structural formula trans-[FeCl2(H2O)4]Cl·2H2O.[10]
Aqueous solution
Aqueous solutions of ferric chloride are characteristically yellow, in contrast to the pale pink solutions of [Fe(H2O)6]3+. According to spectroscopic measurements, the main species in aqueous solutions of ferric chloride are the octahedral complex [FeCl2(H2O)4]+ (stereochemistry unspecified) and the tetrahedral [FeCl4]−.[9]
Preparation
Anhydrous iron(III) chloride may be prepared by treating iron with chlorine:[11]
- 2 Fe + 3 Cl2 → 2 FeCl3
Solutions of iron(III) chloride are produced industrially both from iron and from ore, in a closed-loop process.
- Dissolving iron ore in hydrochloric acid
- Fe3O4 + 8 HCl → FeCl2 + 2 FeCl3 + 4 H2O
- Oxidation of iron(II) chloride with chlorine
- 2 FeCl2 + Cl2 → 2 FeCl3
- Oxidation of iron(II) chloride with oxygen and hydrochloric acid
- 4 FeCl2 + O2 + 4 HCl → 4 FeCl3 + 2 H2O
Heating hydrated iron(III) chloride does not yield anhydrous ferric chloride. Instead, the solid decomposes into hydrochloric acid and iron oxychloride. Hydrated iron(III) chloride can be converted to the anhydrous form by treatment with thionyl chloride.[12] Similarly, dehydration can be effected with trimethylsilyl chloride:[13]
- FeCl3·6H2O + 12 (CH3)3SiCl → FeCl3 + 6 ((CH3)3Si)2O + 12 HCl
Reactions
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When dissolved in water, iron(III) chloride give a strongly acidic solution.[14][9]
When heated with iron(III) oxide at 350 °C, iron(III) chloride gives iron oxychloride.[15]
- FeCl3 + Fe2O3 → 3FeOCl
The anhydrous salt is a moderately strong Lewis acid, forming adducts with Lewis bases such as triphenylphosphine oxide; e.g., FeCl3(OPPh3)2 where Ph is phenyl. It also reacts with other chloride salts to give the yellow tetrahedral [FeCl4]− ion. Salts of [FeCl4]− in hydrochloric acid can be extracted into diethyl ether.
Redox reactions
Iron(III) chloride is a mild oxidizing agent, for example, it oxidizes copper(I) chloride to copper(II) chloride.
- FeCl3 + CuCl → FeCl2 + CuCl2
In a comproportionation reaction, it reacts with iron to form iron(II) chloride:
- 2 FeCl3 + Fe → 3 FeCl2
A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene:[16]
- 2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl
With carboxylate anions
Oxalates react rapidly with aqueous iron(III) chloride to give [Fe(C2O4)3]3−. Other carboxylate salts form complexes; e.g., citrate and tartrate.
With alkali metal alkoxides
Alkali metal alkoxides react to give the metal alkoxide complexes of varying complexity.[17] The compounds can be dimeric or trimeric.[18] In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl3 and sodium ethoxide:[19][20]
- FeCl3 + 3 [CH3CH2O]−Na+ → Fe(OCH2CH3)3 + 3 NaCl
With organometallic compounds
Iron(III) chloride in ether solution oxidizes methyl lithium LiCH3 to give first light greenish yellow lithium tetrachloroferrate(III) Li[FeCl4] solution and then, with further addition of methyl lithium, lithium tetrachloroferrate(II) Li2[FeCl4]:[21]
- 2 FeCl3 + LiCH3 → FeCl2 + Li[FeCl4] + •CH3
- Li[FeCl4] + LiCH3 → Li2[FeCl4] + •CH3
The methyl radicals combine with themselves or react with other components to give mostly ethane C2H6 and some methane CH4.
Uses
Industrial
Iron(III) chloride is used in sewage treatment and drinking water production as a coagulant and flocculant.[22] In this application, FeCl3 in slightly basic water reacts with the hydroxide ion (OH−) to form a floc of iron(III) hydroxide (Fe(OH)3), also formulated as FeO(OH) (ferrihydrite), that can remove suspended materials.
- [Fe(H2O)6]3+ + 4 OH− → [Fe(OH)4(H2O)2]− + 4 H2O → [FeO(OH)2(H2O)]− + 6 H2O
It is also used as a leaching agent in chloride hydrometallurgy,[23] for example in the production of Si from FeSi (Silgrain process by Elkem).[24]
Another important application of iron(III) chloride is etching copper in two-step redox reaction to copper(I) chloride and then to copper(II) chloride in the production of printed circuit boards (PCB).[25]
- FeCl3 + Cu → FeCl2 + CuCl
- FeCl3 + CuCl → FeCl2 + CuCl2
Iron(III) chloride is used as catalyst for the reaction of ethylene with chlorine, forming ethylene dichloride (1,2-dichloroethane), an important commodity chemical, which is mainly used for the industrial production of vinyl chloride, the monomer for making PVC.
- H2C=CH2 + Cl2 → ClCH2CH2Cl
Laboratory use
In the laboratory iron(III) chloride is commonly employed as a Lewis acid for catalyzing reactions such as chlorination of aromatic compounds and Friedel–Crafts reaction of aromatics. It is less powerful than aluminum chloride, but in some cases this mildness leads to higher yields, for example in the alkylation of benzene:
The ferric chloride test is a traditional colorimetric test for phenols, which uses a 1% iron(III) chloride solution that has been neutralized with sodium hydroxide until a slight precipitate of FeO(OH) is formed.[26] The mixture is filtered before use. The organic substance is dissolved in water, methanol or ethanol, then the neutralized iron(III) chloride solution is added—a transient or permanent coloration (usually purple, green or blue) indicates the presence of a phenol or enol.
This reaction is exploited in the Trinder spot test, which is used to indicate the presence of salicylates, particularly salicylic acid, which contains a phenolic OH group.
This test can be used to detect the presence of gamma-hydroxybutyric acid and gamma-butyrolactone,[27] which cause it to turn red-brown.
Other uses
- Used in anhydrous form as a drying reagent in certain reactions.
- Used to detect the presence of phenol compounds in organic synthesis; e.g., examining purity of synthesized Aspirin.
- Used in water and wastewater treatment to precipitate phosphate as iron(III) phosphate.
- Used in wastewater treatment for odor control.
- Used by American coin collectors to identify the dates of Buffalo nickels that are so badly worn that the date is no longer visible.
- Used by bladesmiths and artisans in pattern welding to etch the metal, giving it a contrasting effect, to view metal layering or imperfections.
- Used to etch the widmanstatten pattern in iron meteorites.
- Necessary for the etching of photogravure plates for printing photographic and fine art images in intaglio and for etching rotogravure cylinders used in the printing industry.
- Used to make printed circuit boards (PCBs) by etching copper.
- Used to strip aluminum coating from mirrors.
- Used to etch intricate medical devices.
- Used in veterinary practice to treat overcropping of an animal's claws, particularly when the overcropping results in bleeding.
- Reacts with cyclopentadienylmagnesium bromide in one preparation of ferrocene, a metal-sandwich complex.[28]
- Sometimes used in a technique of Raku ware firing, the iron coloring a pottery piece shades of pink, brown, and orange.
- Used to test the pitting and crevice corrosion resistance of stainless steels and other alloys.
- Used in conjunction with NaI in acetonitrile to mildly reduce organic azides to primary amines.[29]
- Used in an animal thrombosis model.[30]
- Used in an experimental energy storage systems.[31]
- Historically it was used to make direct positive blueprints.[32][33]
- A component of modified Carnoy's solution used for surgical treatment of keratocystic odontogenic tumor (KOT).
- Used as an additive to sodium chloride (NaCl) to produce clear crystals.
Safety
Iron(III) chloride is harmful, highly corrosive and acidic. The anhydrous material is a powerful dehydrating agent.
Although reports of poisoning in humans are rare, ingestion of ferric chloride can result in serious morbidity and mortality. Inappropriate labeling and storage lead to accidental swallowing or misdiagnosis. Early diagnosis is important, especially in seriously poisoned patients.
Natural occurrence
The natural counterpart of FeCl3 is the rare mineral molysite, usually related to volcanic and other-type fumaroles.[34][35]
FeCl3 is also produced as an atmospheric salt aerosol by reaction between iron-rich dust and hydrochloric acid from sea salt. This iron salt aerosol causes about 5% of naturally-occurring oxidization of methane and is thought to have a range of cooling effects.[36]
The atmosphere of the planet Venus is approximately 1% FeCl3.[37][38]
See also
- Verhoeff's stain
- Ferrosilicon
Notes
- An alternative GHS classification from the Japanese GHS Inter-ministerial Committee (2006)[6] notes the possibility of respiratory tract irritation from FeCl3 and differs slightly in other respects from the classification used here.
References
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- Holleman AF, Wiberg E (2001). Wiberg N (ed.). Inorganic Chemistry. San Diego: Academic Press. ISBN 978-0-12-352651-9.
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- Dueñas Díez M, Fjeld M, Andersen E, et al. (2006). "Validation of a compartmental population balance model of an industrial leaching process: The Silgrain process". Chem. Eng. Sci. 61 (1): 229–245. doi:10.1016/j.ces.2005.01.047.
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- Kealy TJ, Pauson PL (1951). "A New Type of Organo-Iron Compound". Nature. 168 (4285): 1040. Bibcode:1951Natur.168.1039K. doi:10.1038/1681039b0. S2CID 4181383.
- Kamal A, Ramana K, Ankati H, et al. (2002). "Mild and efficient reduction of azides to amines: synthesis of fused [2,1-b]quinazolines". Tetrahedron Lett. 43 (38): 6861–6863. doi:10.1016/S0040-4039(02)01454-5.
- Tseng M, Dozier A, Haribabu B, et al. (2006). "Transendothelial migration of ferric ion in FeCl3 injured murine common carotid artery". Thromb. Res. 118 (2): 275–280. doi:10.1016/j.thromres.2005.09.004. PMID 16243382.
- Manohar, Aswin K.; Kim, Kyu Min; Plichta, Edward; Hendrickson, Mary; Rawlings, Sabrina; Narayanan, S. R. (28 October 2015). "A High Efficiency Iron-Chloride Redox Flow Battery for Large-Scale Energy Storage". Journal of the Electrochemical Society. 163 (1): A5118. doi:10.1149/2.0161601jes. ISSN 1945-7111. S2CID 100823390.
- US Patent 241713, Pellet H, "Method of preparing paper", published 1881
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- Oeste, Franz Dietrich; de Richter, Renaud; Ming, Tingzhen; Caillol, Sylvain (January 13, 2017). "Climate engineering by mimicking natural dust climate control: the iron salt aerosol method". Earth System Dynamics. 8 (1): 1–54. Bibcode:2017ESD.....8....1O. doi:10.5194/esd-8-1-2017 – via esd.copernicus.org.
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Further reading
![](../I/Commons-logo.svg.png.webp)
- Lide DR, ed. (1990). CRC Handbook of Chemistry and Physics (71st ed.). Ann Arbor, MI, USA: CRC Press. ISBN 9780849304712.
- Stecher PG, Finkel MJ, Siegmund OH, eds. (1960). The Merck Index of Chemicals and Drugs (7th ed.). Rahway, NJ, USA: Merck & Co.
- Nicholls D (1974). Complexes and First-Row Transition Elements, Macmillan Press, London, 1973. A Macmillan chemistry text. London: Macmillan Press. ISBN 9780333170885.
- Wells AF (1984). Structural Inorganic Chemistry. Oxford science publications (5th ed.). Oxford, UK: Oxford University Press. ISBN 9780198553700.
- March J (1992). Advanced Organic Chemistry (4th ed.). New York: John Wiley & Sons, Inc. pp. 723. ISBN 9780471581482.
- Reich HJ, Rigby HJ, eds. (1999). Acidic and Basic Reagents. Handbook of Reagents for Organic Synthesis. New York: John Wiley & Sons, Inc. ISBN 9780471979258.