Iron(III) chloride#Industrial

Image:Aluminium-trichloride-dimer-3D-balls.png

All forms of ferric chloride are paramagnetic, owing to the presence of unpaired electrons residing in 3d orbitals. Although Fe(III) chloride can be octahedral or tetrahedral (or both, see structure section), all of these forms have five unpaired electrons, one per d-orbital. The high spin d⁵ electronic configuration requires that d-d electronic transitions are spin forbidden, in addition to violating the Laporte rule. This double forbidden-ness results in its solutions being only pale colored. Or, stated more technically, the optical transitions are non-intense. Aqueous ferric sulfate and ferric nitrate, which contain {{chem2|[Fe(H2O)6](3+)}}, are nearly colorless, whereas the chloride solutions are yellow. Thus, the chloride ligands significantly influence the optical properties of the iron center.{{ cite book | title = Inorganic Chemistry | last1 = Housecroft | first1 = C. E. | last2 = Sharpe | first2 = A. G. | year = 2012 | publisher = Prentice Hall | edition = 4th | isbn = 978-0-273-74275-3 | pages = 747 }}{{cite journal|author=Simon A. Cotton|year=2018|title=Iron(III) Chloride and Its Coordination Chemistry |journal=Journal of Coordination Chemistry| volume=71|issue=21|pages=3415–3443|doi=10.1080/00958972.2018.1519188|s2cid=105925459}}

Iron(III) chloride can exist as an anhydrous material and a series of hydrates, which results in distinct structures.

The anhydrous compound is a hygroscopic crystalline solid with a melting point of 307.6 °C. The colour depends on the viewing angle: by reflected light, the crystals appear dark green, but by transmitted light, they appear purple-red. Anhydrous iron(III) chloride has the bismuth(III) iodide structure, with octahedral Fe(III) centres interconnected by two-coordinate chloride ligands.

Iron(III) chloride has a relatively low melting point and boils at around 315 °C. The vapor consists of the dimer {{Chem2|Fe2Cl6}}, much like aluminium chloride. This dimer dissociates into the monomeric {{Chem2|FeCl3}} (with D_3h point group molecular symmetry) at higher temperatures, in competition with its reversible decomposition to give iron(II) chloride and chlorine gas.{{cite book|title=Inorganic Chemistry|vauthors=Holleman AF, Wiberg E|publisher=Academic Press|year=2001|isbn=978-0-12-352651-9|veditors=Wiberg N|location=San Diego}}

Ferric chloride form hydrates upon exposure to water, reflecting its Lewis acidity. All hydrates exhibit deliquescence, meaning that they become liquid by absorbing moisture from the air. Hydration invariably gives derivatives of aquo complexes with the formula {{chem2|[FeCl2(H2O)4]+}}. This cation can adopt either trans or cis stereochemistry, reflecting the relative location of the chloride ligands on the octahedral Fe center. Four hydrates have been characterized by X-ray crystallography: the dihydrate {{chem2|FeCl3*2H2O}}, the disesquihydrate {{chem2|FeCl3*2.5H2O}}, the trisesquihydrate {{chem2|FeCl3*3.5H2O}}, and finally the hexahydrate {{chem2|FeCl3*6H2O}}. These species differ with respect to the stereochemistry of the octahedral iron cation, the identity of the anions, and the presence or absence of water of crystallization. The structural formulas are {{chem2|[trans\sFeCl2(H2O)4][FeCl4]}}, {{chem2|[cis\sFeCl2(H2O)4][FeCl4]*H2O}}, {{chem2|[cis\sFeCl2(H2O)4][FeCl4]*H2O}}, and {{chem2|[trans\sFeCl2(H2O)4]Cl*2H2O}}. The first three members of this series have the tetrahedral tetrachloroferrate ({{chem2|[FeCl4]-}}) anion.{{cite journal |doi=10.1063/1.1712067|title=Crystal Structure of Ferric Chloride Hexahydrate|year=1967|last1=Lind|first1=M. D.|journal=The Journal of Chemical Physics|volume=47|issue=3|pages=990–993|bibcode=1967JChPh..47..990L|doi-access=free}}

File:Iron(III) chloride 2.JPG

Like the solid hydrates, aqueous solutions of ferric chloride also consist of the octahedral {{chem2|[FeCl2(H2O)4]+}} of unspecified stereochemistry. Detailed speciation of aqueous solutions of ferric chloride is challenging because the individual components do not have distinctive spectroscopic signatures. Iron(III) complexes, with a high spin d⁵ configuration, are kinetically labile, which means that ligands rapidly dissociate and reassociate. A further complication is that these solutions are strongly acidic, as expected for aquo complexes of a tricationic metal. Iron aquo complexes are prone to olation, the formation of polymeric oxo derivatives. Dilute solutions of ferric chloride produce soluble nanoparticles with molecular weight of 10⁴, which exhibit the property of "aging", i.e., the structure change or evolve over the course of days.{{cite journal |doi=10.1021/cr00059a003 |title=Hydrolysis of Inorganic Iron(III) Salts |date=1984 |last1=Flynn |first1=Charles M. |journal=Chemical Reviews |volume=84 |pages=31–41 }} The polymeric species formed by the hydrolysis of ferric chlorides are key to the use of ferric chloride for water treatment.

In contrast to the complicated behavior of its aqueous solutions, solutions of iron(III) chloride in diethyl ether and tetrahydrofuran are well-behaved. Both ethers form 1:2 adducts of the general formula FeCl₃(ether)₂. In these complexes, the iron is pentacoordinate.

Several hundred tons of anhydrous iron(III) chloride are produced annually. The principal method, called direct chlorination, uses scrap iron as a precursor:

:{{chem2|2 Fe + 3 Cl2 → 2 FeCl3}}

The reaction is conducted at several hundred degrees such that the product is gaseous. Using excess chlorine guarantees that the intermediate ferrous chloride is converted to the ferric state. A similar but laboratory-scale process also has been described.{{cite book|vauthors=Tarr BR, Booth HS, Dolance A|chapter=Anhydrous Iron(III) Chloride (Ferric Chloride) |year=1950|volume=3|pages=191–194|title=Inorganic Syntheses|doi=10.1002/9780470132340.ch51|isbn=9780470131626 }}{{cite book|author1=H. Lux|chapter=Iron (III) Chloride|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2|pages=1492}}

Aqueous solutions of iron(III) chloride are also produced industrially from a number of iron precursors, including iron oxides:

:{{chem2|Fe2O3 + 6 HCl + 9 H2O → 2 FeCl3(H2O)6}}

In complementary route, iron metal can be oxidized by hydrochloric acid followed by chlorination:

:{{chem2|Fe + 2 HCl → FeCl2 + H2}}

:{{chem2|FeCl2 + 0.5 Cl2 + 6 H2O → FeCl3(H2O)6}}

A number of variables apply to these processes, including the oxidation of iron by ferric chloride and the hydration of intermediates. Hydrates of iron(III) chloride do not readily yield anhydrous ferric chloride. Attempted thermal dehydration yields hydrochloric acid and iron oxychloride. In the laboratory, hydrated iron(III) chloride can be converted to the anhydrous form by treatment with thionyl chloride{{cite book|vauthors=Pray AR, Heitmiller RF, Strycker S, Aftandilian VD, Muniyappan T, Choudhury D, Tamres M|title=Inorganic Syntheses|year=1990|isbn=9780470132593|volume=28|pages=321–323|chapter=Anhydrous Metal Chlorides|doi=10.1002/9780470132593.ch80|display-authors=3}} or trimethylsilyl chloride:{{cite book|vauthors=Boudjouk P, So JH, Ackermann MN, Hawley SE, Turk BE|title=Inorganic Syntheses|year=1992|volume=29|pages=108–111|chapter=Solvated and Unsolvated Anhydrous Metal Chlorides from Metal Chloride Hydrates|doi=10.1002/9780470132609.ch26|isbn=9780470132609|display-authors=3}}

:{{chem2|FeCl3*6H2O + 12 (CH3)3SiCl → FeCl3 + 6 ((CH3)3Si)2O + 12 HCl}}

:{{chem2|FeCl3*6H2O + 6 SOCl2 → FeCl3 + 6 SO2 + 12 HCl}}

Being high spin d⁵ electronic configuration iron(III) chlorides are labile, meaning that its Cl- and H₂O ligands exchange rapidly with free chloride and water. In contrast to their kinetic lability, iron(III) chlorides are thermodynamically robust, as reflected by the vigorous methods applied to their synthesis, as described above.

Aside from lability, which applies to anhydrous and hydrated forms, the reactivity of anhydrous ferric chloride reveals two trends: It is a Lewis acid and an oxidizing agent.

Reactions of anhydrous iron(III) chloride reflect its description as both oxophilic and a hard Lewis acid. Myriad manifestations of the oxophiliicty of iron(III) chloride are available. When heated with iron(III) oxide at 350 °C it reacts to give iron oxychloride:

{{Cite book|title=Inorganic Syntheses|vauthors=Kikkawa S, Kanamaru F, Koizumi M, Rich SM, Jacobson A|publisher=John Wiley & Sons, Inc.|year=1984|isbn=9780470132531|veditors=Holt SL Jr|pages=86–89|chapter=Layered Intercalation Compounds|volume=22 |doi=10.1002/9780470132531.ch17|display-authors=3}}

:{{chem2|FeCl3 + Fe2O3 → 3FeOCl}}

Alkali metal alkoxides react to give the iron(III) alkoxide complexes. These products have more complicated structures than anhydrous iron(III) chloride.{{Cite book|url=https://books.google.com/books?id=rPzaMRjK8pQC|title=The Chemistry of Metal Alkoxides|publisher=Springer Science|year=2002|isbn=0306476576|veditors=Turova NY, Turevskaya EP, Kessler VG, Yanovskaya MI|pages=481|chapter=12.22.1 Synthesis|display-editors=3}}{{Cite book|title=Alkoxo and aryloxo derivatives of metals|vauthors=Bradley DC, Mehrotra RC, Rothwell I, Singh A|publisher=Academic Press|year=2001|isbn=9780121241407|location=San Diego|pages=69|chapter=3.2.10. Alkoxides of later 3d metals|oclc=162129468|display-authors=3|chapter-url=https://books.google.com/books?id=ixNEpx8aDHUC&pg=PA69}} In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between {{Chem2|FeCl3}} and sodium ethoxide:

:{{chem2|FeCl3 + 3 CH3CH2ONa → "Fe(OCH2CH3)3" + 3 NaCl}}

Iron(III) chloride forms a 1:2 adduct with Lewis bases such as triphenylphosphine oxide; e.g., {{Chem2|FeCl3(OP(C6H5)3)2}}. The related 1:2 complex {{chem2|1=FeCl3(OEt2)2, where Et = C2H5)}}, has been crystallized from ether solution.{{cite journal |doi=10.1002/zaac.200300008|title=Alkoxo-Verbindungen des dreiwertigen Eisen: Synthese und Charakterisierung von [Fe2(Ot Bu)6], [Fe2Cl2(Ot Bu)4], [Fe2Cl4(Ot Bu)2] und [N(n Bu)4]2[Fe6OCl6(OMe)12] |year=2003 |last1=Spandl |first1=Johann |last2=Kusserow |first2=M. |last3=Brüdgam |first3=I. |journal=Zeitschrift für anorganische und allgemeine Chemie |volume=629 |issue=6 |pages=968–974 |doi-access=free }}

Iron(III) chloride also reacts with tetraethylammonium chloride to give the yellow salt of the tetrachloroferrate ion ({{Chem2|(Et4N)[FeCl4]}}). Similarly, combining FeCl₃ with NaCl and KCl gives {{Chem2|Na[FeCl4]}} and {{Chem2|K[FeCl4]}}, respectively.{{cite journal |title= The Reaction of Ferric Chloride with Sodium and Potassium Chlorides |first1= Charles M. Jr. |last1= Cook |first2= Wendell E. Jr. |last2= Dunn |journal= J. Phys. Chem. |year= 1961 |volume= 65 |issue= 9 |pages= 1505–1511 |doi= 10.1021/j100905a008 }}

In addition to these simple stoichiometric reactions, the Lewis acidity of ferric chloride enables its use in a variety of acid-catalyzed reactions as described below in the section on organic chemistry.

In terms of its being an oxidant, iron(III) chloride oxidizes iron powder to form iron(II) chloride via a comproportionation reaction:

:{{chem2|2 FeCl3 + Fe → 3 FeCl2}}

A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl₃ with chlorobenzene:{{cite book | author = P. Kovacic and N. O. Brace | title = Inorganic Syntheses | year = 1960 | volume = 6 | pages = 172–173 | doi = 10.1002/9780470132371.ch54 | chapter = Iron(II) Chloride| isbn = 9780470132371 }}

:{{chem2|2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl}}

iron(III) chloride releases chlorine gas when heated above 160 °C, generating ferrous chloride:

:{{chem2|2FeCl3 → 2FeCl2 + Cl2}}

To suppress this reaction, the preparation of iron(III) chloride requires an excess of chlorinating agent, as discussed above.

Unlike the anhydrous material, hydrated ferric chloride is not a particularly strong Lewis acid since water ligands have quenched the Lewis acidity by binding to Fe(III). Instead, it is a Brønsted-Lowry acid, as the hydrogen atoms on the water ligands become more acidic when the water ligands bond to Fe(III).

Like the anhydrous material, hydrated ferric chloride is oxophilic. For example, oxalate salts react rapidly with aqueous iron(III) chloride to give {{Chem2|[Fe(C2O4)3](3−)}}, known as ferrioxalate. Other carboxylate sources, e.g., citrate and tartrate, bind as well to give carboxylate complexes. The affinity of iron(III) for oxygen ligands was the basis of qualitative tests for phenols. Although superseded by spectroscopic methods, the ferric chloride test is a traditional colorimetric test.{{cite book|title=Vogel's Textbook of Practical Organic Chemistry|url=https://archive.org/details/Vogels_Textbook_of_Practical_Organic_Chemistry_5ed_1989_Longman_WW|vauthors=Furniss BS, Hannaford AJ, Smith PW, Tatchell AR|publisher=Longman/Wiley|year=1989|isbn=9780582462366|edition=5th|location=New York|display-authors=3|page=1213}} The affinity of iron(III) for phenols is exploited in the Trinder spot test.{{cite journal |author1=James A. King |author2=Alan B. Storrow |author3=Jeff A. Finkelstein |title=Urine Trinder Spot Test: A Rapid Salicylate Screen for the Emergency Department |journal=Annals of Emergency Medicine |date=1995 |volume=26 |issue=3 |pages=330–333 |doi=10.1016/S0196-0644(95)70082-X |pmid=7661424 |language=en}}

Aqueous iron(III) chloride serves as a one-electron oxidant illustrated by its reaction with copper(I) chloride to give copper(II) chloride and iron(II) chloride.

:{{chem2|FeCl3 + CuCl → FeCl2 + CuCl2}}

This fundamental reaction is relevant to the use of ferric chloride solutions in etching copper.

The interaction of anhydrous iron(III) chloride with organolithium and organomagnesium compounds has been examined often. These studies are enabled because of the solubility of FeCl₃ in ethereal solvents, which avoids the possibility of hydrolysis of the nucleophilic alkylating agents. Such studies may be relevant to the mechanism of FeCl₃-catalyzed cross-coupling reactions.{{cite journal |doi=10.1039/C5QI00295H|title=Recent Advances in Iron-Catalysed Cross Coupling Reactions and Their Mechanistic Underpinning |year=2016 |last1=Mako |first1=T. L. |last2=Byers |first2=J. A. |journal=Inorganic Chemistry Frontiers |volume=3 |issue=6 |pages=766–790 }} The isolation of organoiron(III) intermediates requires low-temperature reactions, lest the [FeR₄]⁻ intermediates degrade. Using methylmagnesium bromide as the alkylation agent, salts of Fe(CH₃)₄]⁻ have been isolated.{{cite journal |doi=10.1016/j.poly.2018.10.041|title=Synthesis and Characterization of a Sterically Encumbered Homoleptic Tetraalkyliron(III) Ferrate Complex |year=2019 |last1=Sears |first1=Jeffrey D. |last2=Muñoz |first2=Salvador B. |last3=Cuenca |first3=Maria Camila Aguilera |last4=Brennessel |first4=William W. |last5=Neidig |first5=Michael L. |journal=Polyhedron |volume=158 |pages=91–96 |pmid=31031511 |pmc=6481957 }} and references therein. Illustrating the sensitivity of these reactions, methyl lithium {{Chem2|LiCH3}} reacts with iron(III) chloride to give lithium tetrachloroferrate(II) {{Chem2|Li2[FeCl4]}}:{{Cite journal|vauthors=Berthold HJ, Spiegl HJ|date=1972|title=Über die Bildung von Lithiumtetrachloroferrat(II) Li₂FeCl₄ bei der Umsetzung von Eisen(III)-chlorid mit Lithiummethyl (1:1) in ätherischer Lösung|journal=Z. Anorg. Allg. Chem.|language=de|volume=391|issue=3|pages=193–202|doi=10.1002/zaac.19723910302}}

:{{chem2|2 FeCl3 + LiCH3 → FeCl2 + Li[FeCl4] + 0.5 CH3CH3}}

:{{chem2|Li[FeCl4] + LiCH3 → Li2[FeCl4] + 0.5 CH3CH3}}

To a significant extent, iron(III) acetylacetonate and related beta-diketonate complexes are more widely used than FeCl₃ as ether-soluble sources of ferric ion. These diketonate complexes have the advantages that they do not form hydrates, unlike iron(III) chloride, and they are more soluble in relevant solvents.

Cyclopentadienyl magnesium bromide undergoes a complex reaction with iron(III) chloride, resulting in ferrocene:{{cite journal|vauthors=Kealy TJ, Pauson PL|year=1951|title=A New Type of Organo-Iron Compound|journal=Nature|volume=168|issue=4285|pages=1040|doi=10.1038/1681039b0|bibcode=1951Natur.168.1039K|s2cid=4181383}}

:{{chem2|3 C5H5MgBr + FeCl3 -> Fe(C5H5)2 + 1/n (C5H5)_{n} + 3 MgBrCl}}

This conversion, although not of practical value, was important in the history of organometallic chemistry where ferrocene is emblematic of the field.{{cite journal|title = Ferrocene—how it all began| vauthors = Pauson PL |author-link = Peter Pauson|journal = Journal of Organometallic Chemistry|volume = 637–639|year = 2001|pages = 3–6|doi = 10.1016/S0022-328X(01)01126-3}}

The largest applications of iron(III) chloride are sewage treatment and drinking water production. By forming highly dispersed networks of Fe-O-Fe containing materials, ferric chlorides serve as coagulant and flocculants.{{cite book|url=http://www.akzonobel.com/ic/system/images/AkzoNobel_WTCBrochureENG_tcm18-9982.pdf|title=Water Treatment Chemicals|publisher=Akzo Nobel Base Chemicals|year=2007|access-date=26 Oct 2007|url-status=dead|archive-url=https://web.archive.org/web/20100813083540/http://www.akzonobel.com/ic/system/images/AkzoNobel_WTCBrochureENG_tcm18-9982.pdf|archive-date=13 August 2010}} In this application, an aqueous solution of {{Chem2|FeCl3}} is treated with base to form a floc of iron(III) hydroxide ({{chem2|Fe(OH)3}}), also formulated as FeO(OH) (ferrihydrite). This floc facilitates the separation of suspended materials, clarifying the water.{{cite book |doi=10.1002/14356007.a14_591 |chapter=Iron Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2000 |last1=Wildermuth |first1=Egon |last2=Stark |first2=Hans |last3=Friedrich |first3=Gabriele |last4=Ebenhöch |first4=Franz Ludwig |last5=Kühborth |first5=Brigitte |last6=Silver |first6=Jack |last7=Rituper |first7=Rafael |isbn=3527306730 }}

Iron(III) chloride is also used to remove soluble phosphate from wastewater. Iron(III) phosphate is insoluble and thus precipitates as a solid.{{cite web |title= Phosphorus Treatment and Removal Technologies |date= June 2006 |url= https://www.pca.state.mn.us/sites/default/files/wq-wwtp9-02.pdf |publisher= Minnesota Pollution Control Agency }} One potential advantage of its use in water treatment, is that the ferric ion oxidizes (deodorizes) hydrogen sulfide.{{cite journal |title= Ferric chloride for odour control: studies from wastewater treatment plants in India |first1= T. C. |last1= Prathna |first2= Ankit |last2= Srivastava |journal= Water Practice and Technology |year= 2021 |volume= 16 |issue= 1 |pages= 35–41 |doi= 10.2166/wpt.2020.111 |s2cid= 229396639 |doi-access= free }}

It is also used as a leaching agent in chloride hydrometallurgy,{{cite journal|vauthors=Park KH, Mohapatra D, Reddy BR|year=2006|title=A study on the acidified ferric chloride leaching of a complex (Cu–Ni–Co–Fe) matte|journal=Separation and Purification Technology|volume=51|issue=3|pages=332–337|doi=10.1016/j.seppur.2006.02.013}} for example in the production of Si from FeSi (Silgrain process by Elkem).{{cite journal|display-authors=3|vauthors=Dueñas Díez M, Fjeld M, Andersen E, Lie B|year=2006|title=Validation of a compartmental population balance model of an industrial leaching process: The Silgrain process|journal=Chem. Eng. Sci.|volume=61|issue=1|pages=229–245|doi=10.1016/j.ces.2005.01.047|bibcode=2006ChEnS..61..229D }}

In another commercial application, a solution of iron(III) chloride is useful for etching copper according to the following equation:

:{{chem2|2 FeCl3 + Cu -> 2 FeCl2 + CuCl2}}

The soluble copper(II) chloride is rinsed away, leaving a copper pattern. This chemistry is used in the production of printed circuit boards (PCB).{{cite book|title=Chemistry of the Elements|vauthors=Greenwood NN, Earnshaw A|publisher=Butterworth-Heinemann|year=1997|isbn=9780750633659|edition=2nd|location=Oxford|pages=1084}}

Iron(III) chloride is used in many other hobbies involving metallic objects.{{cite web |author1=John David Graham |title=Safer Printmaking—Intaglio |url=https://research-groups.usask.ca/saferprintmaking/intaglio.php |website=University of Saskatchewan |access-date=5 February 2024}}{{cite web|last1=Harris|first1=Paul|last2=Hartman|first2=Ron|last3=Hartman|first3=James|title=Etching Iron Meteorites|url=http://www.meteorite-times.com/articles/etching-iron-meteorites/|publisher=Meteorite Times|access-date=October 14, 2016|date=November 1, 2002}}{{cite web |author1=Mike Lockwood |author2=Carl Zambuto |title=A message about mirror coating and recoating |url=https://www.loptics.com/articles/coatingrisk/coatingrisk.html |website=Lockwood Custom Optics, Inc. |publisher=Lockwood Custom Optics |access-date=5 February 2024}}{{cite web |author1=CoinValueLookup |title=Buffalo Nickel No Date Value: How Much Is It Worth Today? |url=https://www.coinvaluelookup.com/indian-head-nickel-no-date-value/ |website=CoinValueLookup |date=13 December 2023 |access-date=5 February 2024}}{{cite book |first1= David |last1= Scott |first2= Roland |last2= Schwab |title= Metallography in Archaeology and Art |publisher= Springer |year= 2019 |series= Cultural Heritage Science |chapter= 3.1.4. Etching |doi= 10.1007/978-3-030-11265-3 |isbn= 978-3-030-11265-3 |s2cid= 201676001 }}

File:UJIMUV.jpg

In industry, iron(III) chloride is used as a catalyst for the reaction of ethylene with chlorine, forming ethylene dichloride (1,2-dichloroethane):{{cite book |doi=10.1002/14356007.o06_o01.pub2|chapter=Chloroethanes and Chloroethylenes |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2014 |last1=Dreher |first1=Eberhard-Ludwig |last2=Beutel |first2=Klaus K. |last3=Myers |first3=John D. |last4=Lübbe |first4=Thomas |last5=Krieger |first5=Shannon |last6=Pottenger |first6=Lynn H. |pages=1–81 |isbn=9783527306732 }}

:{{chem2|H2C\dCH2 + Cl2 → ClCH2CH2Cl}}

Ethylene dichloride is a commodity chemical, which is mainly used for the industrial production of vinyl chloride, the monomer for making PVC.{{Cite web |title = Toxic Substances – 1,2-Dichloroethane |url = https://wwwn.cdc.gov/TSP/index.aspx?toxid=110 |website = ATSDR |access-date = 2023-08-30}}

Illustrating it use as a Lewis acid, iron(III) chloride catalyses electrophilic aromatic substitution and chlorinations. In this role, its function is similar to that of aluminium chloride. In some cases, mixtures of the two are used.{{cite journal |title= Mixed Catalysis in the Friedel and Crafts Reaction. The Yields in Typical Reactions using Ferric Chloride–Aluminum Chloride Mixtures as Catalysts |first1= W. A. |last1= Riddell |first2= C. R. |last2= Noller |journal= J. Am. Chem. Soc. |year= 1932 |volume= 54 |issue= 1 |pages= 290–294 |doi= 10.1021/ja01340a043 }}

Although iron(III) chlorides are seldom used in practical organic synthesis, they have received considerable attention as reagents because they are inexpensive, earth abundant, and relatively nontoxic. Many experiments probe both its redox activity and its Lewis acidity. For example, iron(III) chloride oxidizes naphthols to naphthoquinones:{{cite journal |author=Louis F. Fieser|doi=10.15227/orgsyn.017.0068|title=1,2-Naphthoquinone |journal=Organic Syntheses |year=1937 |volume=17 |page=68 }} 3-Alkylthiophenes are polymerized to polythiophenes upon treatment with ferric chloride.{{cite journal |doi=10.1021/acs.chemrev.8b00773 |title=Molecular Design, Synthetic Strategies, and Applications of Cationic Polythiophenes |date=2019 |last1=So |first1=Regina C. |last2=Carreon-Asok |first2=Analyn C. |journal=Chemical Reviews |volume=119 |issue=21 |pages=11442–11509 |pmid=31580649 |s2cid=206542971 }} Iron(III) chloride has been shown to promote C-C coupling reaction.{{cite journal |doi=10.1021/acs.chemrev.0c01096 |title=Carbonyl–Olefin Metathesis |date=2021 |last1=Albright |first1=Haley |last2=Davis |first2=Ashlee J. |last3=Gomez-Lopez |first3=Jessica L. |last4=Vonesh |first4=Hannah L. |last5=Quach |first5=Phong K. |last6=Lambert |first6=Tristan H. |last7=Schindler |first7=Corinna S. |journal=Chemical Reviews |volume=121 |issue=15 |pages=9359–9406 |pmid=34133136 |pmc=9008594 }}

Several reagents have been developed based on supported iron(III) chloride. On silica gel, the anhydrous salt has been applied to certain dehydration and pinacol-type rearrangement reactions. A similar reagent but moistened induces hydrolysis or epimerization reactions.{{cite book |doi=10.1002/047084289X.ri059 |chapter=Iron(III) Chloride-Silica Gel |title=Encyclopedia of Reagents for Organic Synthesis |year=2001 |last1=White |first1=Andrew D. |isbn=0471936235 }} On alumina, ferric chloride has been shown to accelerate ene reactions.{{cite book |doi=10.1002/047084289X.ri057 |chapter=Iron(III) Chloride-Alumina |title=Encyclopedia of Reagents for Organic Synthesis |year=2001 |last1=White |first1=Andrew D. |isbn=0471936235 }}

When pretreated with sodium hydride, iron(III) chloride gives a hydride reducing agent that convert alkenes and ketones into alkanes and alcohols, respectively.{{cite book |doi=10.1002/047084289X.ri060|chapter=Iron(III) Chloride-Sodium Hydride |title=Encyclopedia of Reagents for Organic Synthesis |year=2001 |last1=White |first1=Andrew D. |isbn=0471936235 }}

File:FeCl3oxidation.svg

Iron(III) chloride is a component of useful stains, such as Carnoy's solution, a histological fixative with many applications. Also, it is used to prepare Verhoeff's stain.{{cite encyclopedia |last1=Mallory |last2=Sheehan |last3=Hrapchak |editor1-last=Carson |editor1-first=Freida |editor2-last=Cappellano |editor2-first=Christa Hladik |title=Histotechnology – A Self-Instructional Text |publisher=ASCP Press |location=Chicago |date=1990 | url =http://tvmouse.ucdavis.edu/bcancercd/52/prcl_elastic.html | chapter =Verhoeff's Elastic Stain | via =The Visible Mouse Project, U.C. Davis | access-date =2 January 2013 }}

Like many metal halides, {{chem2|FeCl3}} naturally occurs as a trace mineral. The rare mineral molysite is usually associated with volcanoes and fumaroles.{{cite web |title=Molysite |url=https://www.mindat.org/min-2749.html |website=mindat.org |publisher=Mindat |access-date=5 February 2024}}{{cite web |title=IMA list of Minerals |url=https://mineralogy-ima.org/Minlist.htm |website=International Mineralogical Association |date=21 March 2011 |access-date=5 February 2024}}

{{chem2|FeCl3}}-based aerosol are produced by a reaction between iron-rich dust and hydrochloric acid from sea salt. This iron salt aerosol causes about 1-5% of naturally-occurring oxidization of methane and is thought to have a range of cooling effects; thus, it has been proposed as a catalyst for Atmospheric Methane Removal.{{Cite journal|url=https://esd.copernicus.org/articles/8/1/2017/|title=Climate engineering by mimicking natural dust climate control: the iron salt aerosol method|first1=Franz Dietrich|last1=Oeste|first2=Renaud|last2=de Richter|first3=Tingzhen|last3=Ming|first4=Sylvain|last4=Caillol|date=January 13, 2017|journal=Earth System Dynamics|volume=8|issue=1|pages=1–54|via=esd.copernicus.org|doi=10.5194/esd-8-1-2017|bibcode=2017ESD.....8....1O|doi-access=free}}

The clouds of Venus are hypothesized to contain approximately 1% {{chem2|FeCl3}} dissolved in sulfuric acid.{{cite journal |title=Chemical composition of the atmosphere of Venus |last1=Krasnopolsky |first1=V. A. |last2=Parshev |first2=V. A. |journal=Nature |volume=292 |issue=5824 |pages=610–613 |date=1981 |doi=10.1038/292610a0 |bibcode=1981Natur.292..610K|s2cid=4369293 }}{{cite journal |title=Chemical composition of Venus atmosphere and clouds: Some unsolved problems |first=Vladimir A. |last=Krasnopolsky |date=2006 |journal=Planetary and Space Science |volume=54 |issue=13–14 |pages=1352–1359 |doi=10.1016/j.pss.2006.04.019 |bibcode=2006P&SS...54.1352K}}

Iron(III) chlorides are widely used in the treatment of drinking water, so they pose few problems as poisons, at low concentrations.{{synthesis inline|date=June 2024}} Nonetheless, anhydrous iron(III) chloride, as well as concentrated {{chem2|FeCl3}} aqueous solution, is highly corrosive, and must be handled using proper protective equipment.{{cite book |doi=10.1002/047084289X.ri054.pub2|chapter=Iron(III) Chloride |title=Encyclopedia of Reagents for Organic Synthesis |year=2006 |last1=White |first1=Andrew D. |last2=Gallou |first2=Fabrice |isbn=0471936235 }}

{{reflist|group=Note}}

{{reflist|30em}}

{{Commons category|Iron(III) chloride}}

1. {{Cite book|title=CRC Handbook of Chemistry and Physics|publisher=CRC Press|year=1990|isbn=9780849304712|veditors=Lide DR|edition=71st|location=Ann Arbor, Michigan, US}}
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{{Iron compounds}}

{{Chlorides}}

{{DEFAULTSORT:Iron(Iii) Chloride}}

Category:Chlorides

Category:Iron(III) compounds

Category:Metal halides

Category:Coordination complexes

Category:Deliquescent materials

Category:Dehydrating agents

Category:Acid catalysts