Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Iron(III) chloride: Difference between pages

{{good article}}

{{Short description|Inorganic compound}}

{{cs1 config|name-list-style=vanc}}

{{Chembox <!-- infobox -->

|Verifiedfields = changed

|Watchedfields = changed

|verifiedrevid = 476995973

|ImageFileL1 = Iron(III) chloride anhydrate.jpg

|ImageCaptionL1 = Iron(III) chloride (anhydrous)

|ImageFileR1 = Хлорид железа.jpg

|ImageCaptionR1 = Iron(III) chloride (hydrate)

|ImageFileL2 = Iron-trichloride-sheet-3D-polyhedra.png

|ImageFileR2 = Iron-trichloride-sheets-stacking-3D-polyhedra.png

|IUPACName = Iron(III) chloride<br />Iron trichloride

|OtherNames = {{ubl

|Ferric chloride

|Molysite

|Flores martis}}

|Section1={{Chembox Identifiers

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|ChemSpiderID = 22792

|InChI = 1S/3ClH.Fe/h3*1H;/q;;;+3/p-3

|InChIKey = RBTARNINKXHZNM-DFZHHIFOAF

|ChEBI_Ref = {{ebicite|correct|EBI}}

|ChEBI = 30808

|SMILES = Cl[Fe](Cl)Cl

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|StdInChI = 1S/3ClH.Fe/h3*1H;/q;;;+3/p-3

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|StdInChIKey = RBTARNINKXHZNM-UHFFFAOYSA-K

|InChIKey1 = RBTARNINKXHZNM-UHFFFAOYSA-K

|CASNo = 7705-08-0

|CASNo_Ref = {{cascite|correct|CAS}}

|CASNo2_Ref = {{cascite|correct|CAS}}

|CASNo2 = 10025-77-1

|CASNo2_Comment = (hexahydrate)

|CASNo3_Ref = {{cascite|correct|CAS}}

|CASNo3 = 54862-84-9

|CASNo3_Comment = (dihydrate)

|CASNo4 = 64333-00-2

|CASNo4_Comment = (3.5hydrate)

|UNII_Ref = {{fdacite|correct|FDA}}

|UNII = U38V3ZVV3V

|UNII2_Ref = {{fdacite|correct|FDA}}

|UNII2 = 0I2XIN602U

|UNII2_Comment = (hexahydrate)

|UNII3_Ref = {{fdacite|correct|FDA}}

|UNII3 = Y048945596

|UNII3_Comment = (dihydrate)

|EINECS = 231-729-4

|PubChem = 24380

|RTECS = LJ9100000

|UNNumber = {{ubl

|1773 (anhydrous)

|2582 (aqueous solution)}}}}

|Section2={{Chembox Properties

|Formula = {{chem2|FeCl3}}

|MolarMass = {{ubl

|162.204{{nbsp}}g/mol (anhydrous)

|270.295{{nbsp}}g/mol (hexahydrate)<ref name=crc/>}}

|Appearance = Green-black by reflected light; purple-red by transmitted light; yellow solid as hexahydrate; brown as aqueous solution

|Odor = Slight [[hydrochloric acid|HCl]]

|Density = {{ubl

|2.90{{nbsp}}g/cm³ (anhydrous)

|1.82{{nbsp}}g/cm³ (hexahydrate)<ref name=crc/>}}

|MeltingPtC = 307.6

|MeltingPt_notes = (anhydrous)<br />{{convert|37|C|F K}} (hexahydrate)<ref name=crc>{{RubberBible92nd|page=4.69}}</ref>

|BoilingPt = {{ubl

|{{convert|316|C|F K}} (anhydrous, decomposes)<ref name=crc/>

|{{convert|280|C|F K}} (hexahydrate, decomposes)}}

|Solubility = 912{{nbsp}}g/L (anhydrous or hexahydrate, 25{{nbsp}}°C)<ref name=crc/>

|SolubleOther = {{ubl

|{{nbsp}}

|630&nbsp;g/L (18&nbsp;°C)

|Highly soluble

|830&nbsp;g/L

|Highly soluble}}

|Solvent = {{ubl

|[[Acetone]]

|[[Methanol]]

|[[Ethanol]]

|[[Diethyl ether]]<ref name=crc/>}}

|Viscosity = 12&nbsp;c[[Poise (unit)|P]] (40%&nbsp;solution)

|MagSus = +13,450·10⁻⁶{{nbsp}}cm³/mol<ref>{{RubberBible92nd|page=4.133}}</ref>}}

|Section5={{Chembox Structure

|CrystalStruct = [[Hexagonal crystal system|Hexagonal]], [[Pearson symbol|hR24]]

|SpaceGroup = R{{overline|3}}, No. 148<ref name="str">{{cite journal|vauthors=Hashimoto S, Forster K, Moss SC|year=1989|title=Structure refinement of an FeCl₃ crystal using a thin plate sample|journal=[[Journal of Applied Crystallography|J. Appl. Crystallogr.]]|volume=22|issue=2|pages=173–180|doi=10.1107/S0021889888013913|bibcode=1989JApCr..22..173H }}</ref>

|Coordination = [[Octahedral]]

|LattConst_a = 0.6065{{nbsp}}nm

|LattConst_b = 0.6065{{nbsp}}nm

|LattConst_c = 1.742{{nbsp}}nm

|LattConst_alpha = 90

|LattConst_beta = 90

|LattConst_gamma = 120

|UnitCellFormulas = 6

|Section3={{Chembox Hazards

| Hazards_ref = <ref>{{GHS class NZ|id=10764|access-date=19 Sep 2010}}</ref><ref>[http://webcomm.bcd.tamhsc.edu/bcdfacilities/msds9.html Various suppliers], collated by the Baylor College of Dentistry, [[Texas A&M University]]. (accessed 2010-09-19)</ref>{{refn|An alternative GHS classification from the Japanese GHS Inter-ministerial Committee (2006)<ref>{{GHS class JP|id=831|access-date=19 Sep 2010}}</ref> notes the possibility of respiratory tract irritation from {{Chem2|FeCl3}} and differs slightly in other respects from the classification used here.|group=Note}}

|ExternalSDS = {{ICSC-small|1499}}

|GHSPictograms = {{GHS05|Corr. Met. 1; Skin Corr. 1C; Eye Dam. 1}}{{GHS07|Acute Tox. 4 (oral)}}

|GHSSignalWord = DANGER

|HPhrases = {{H-phrases|290|302|314}}

|PPhrases = {{P-phrases|234|260|264|270|273|280| 301+312|301+330+331|303+361+353|363|304+340|310|321|305+351+338|390| 405|406|501}}

|FlashPt = Non-flammable

|NFPA-F = 0 | NFPA-H = 2 | NFPA-R = 0 | NFPA-S =

|REL = TWA 1{{nbsp}}mg/m³<ref>{{PGCH|0346}}</ref>}}

|Section4={{Chembox Related

|OtherAnions = {{ubl

|[[Iron(III) fluoride]]

|[[Iron(III) bromide]]}}

|OtherCations = {{ubl

|[[Iron(II) chloride]]

|[[Manganese(II) chloride]]

|[[Cobalt(II) chloride]]

|[[Ruthenium(III) chloride]]}}

|OtherFunction = {{ubl

|[[Iron(II) sulfate]]

|[[Aluminium chloride|Polyaluminium chloride]]}}

|OtherFunction_label = [[Flocculation|coagulants]]

}}}}

'''Iron(III) chloride''' describes the inorganic compounds with the formula {{chem2|[[Iron|Fe]][[chloride|Cl]]3}}(H₂O)_x. Also called '''ferric chloride''', these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated forms which are both [[hygroscopic]]. They feature iron in its +3 [[oxidation state]]. The anhydrous derivative is a [[Lewis acid]], while all forms are mild oxidizing agents. It is used as a [[water treatment|water cleaner]] and as an [[Chemical milling|etchant]] for metals.

==Electronic and optical properties==

[[Image:Aluminium-trichloride-dimer-3D-balls.png|thumb|left|144px|Anhydrous iron(III) chloride evaporates at relatively low temperatures to give the bitetrahedral dimer.]]

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|d-orbital]]. The [[spin states (d electrons)|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.<ref>{{ 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 }}</ref><ref name=Cotton>{{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}}</ref>

==Structure==

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

===Anhydrous===

The [[anhydrous]] compound is a hygroscopic crystalline solid with a melting point of 307.6&nbsp;°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|{{Chem2|BiI3}}]] structure, with [[octahedral]] Fe(III) centres interconnected by two-coordinate chloride [[ligand]]s.<ref name="str"/><ref name="UllmannFe" />

Iron(III) chloride has a relatively low melting point and boils at around 315&nbsp;°C. The vapor consists of the [[Dimer (chemistry)|dimer]] {{Chem2|Fe2Cl6}}, much like [[aluminium chloride]]. This dimer dissociates into the [[monomeric]] {{Chem2|FeCl3}} (with D_3h [[symmetry group|point group]] [[molecular symmetry]]) at higher temperatures, in competition with its reversible decomposition to give [[iron(II) chloride]] and [[chlorine]] gas.<ref>{{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}}</ref>

===Hydrates===

Ferric chloride form [[hydrate]]s 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 complex]]es with the formula {{chem2|[FeCl2(H2O)4]+}}. This cation can adopt either [[cis-trans isomer|''trans'' or ''cis'']] [[stereochemistry]], reflecting the relative location of the chloride [[ligand]]s on the [[octahedral molecular geometry|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]].<ref name=Cotton/> 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.<ref>{{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}}</ref>

===Solution===

[[File:Iron(III) chloride 2.JPG|thumb|left|A brown, acidic solution of iron(III) chloride.]]

Like the solid hydrates, aqueous solutions of ferric chloride also consist of the octahedral {{chem2|[FeCl2(H2O)4]+}} of unspecified stereochemistry.<ref name=Cotton/> 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, is kinetically labile, which means that ligands rapidly dissociate and reassociate. A further complication is that these solutions are strongly acidic, as expected for [[aquo complex]]es of a tricationic metal. Iron aquo complexes are prone to [[olation]], the formation of [[polymeric]] [[oxo complex|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.<ref>{{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 }}</ref> 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 [[ether]]s form 1:2 [[adduct]]s of the general formula FeCl₃(ether)₂. In these complexes, the iron is pentacoordinate.<ref name=ZaaC/>

==Preparation==

Several hundred thousand kilograms of anhydrous iron(III) chloride are produced annually. The principal method, called ''direct chlorination'', uses scrap iron as a precursor:<ref name="UllmannFe" />

:{{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.<ref name=UllmannFe/> A similar but laboratory-scale process also has been described.<ref>{{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 }}</ref><ref name=Brauer>{{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}}</ref>

''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:<ref name="UllmannFe" />

:{{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.<ref name="UllmannFe" /> 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]]<ref>{{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}}</ref> or [[trimethylsilyl chloride]]:<ref>{{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}}</ref>

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

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

==Reactions==

Being [[spin states (d electrons)|high spin]] d⁵ electronic configuration iron(III) chlorides are [[labile]], meaning that its Cl- and H₂O ligands exchange rapidly with free chloride and water.<ref name="Cotton" /><ref name="greenwood" /> 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.

===Anhydrous FeCl₃===

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 [[redox|oxidizing agent]].<ref name="EROS" />

Reactions of anhydrous iron(III) chloride reflect its description as both [[oxophilic]] and a [[HSAB theory|hard Lewis acid]]. Myriad manifestations of the oxophiliicty of iron(III) chloride are available. When heated with [[iron(III) oxide]] at 350&nbsp;°C it reacts to give [[iron oxychloride]]:<ref>

{{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}}</ref>

:{{chem2|FeCl3 + Fe2O3 → 3FeOCl}}

Alkali metal [[alkoxide]]s react to give the iron(III) [[metal alkoxide|alkoxide complex]]es. These products have more complicated structures than anhydrous iron(III) chloride.<ref>{{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}}</ref><ref>{{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}}</ref> 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 base]]s 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.<ref name=ZaaC>{{cite journal |doi=10.1002/zaac.200300008|title=Alkoxo-Verbindungen des dreiwertigen Eisen: Synthese und Charakterisierung von &#91;Fe2(Ot ''Bu'')6&#93;, &#91;Fe2Cl2(Ot ''Bu'')4&#93;, &#91;Fe2Cl4(Ot ''Bu'')2&#93; und &#91;N(n ''Bu'')4&#93;2&#91;Fe6OCl6(OMe)12&#93; |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 }}</ref>

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.<ref>{{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 }}</ref>

In addition to these simple [[stoichiometric]] reactions, the Lewis acidity of ferric chloride enables its use in a variety of acid-[[catalysis|catalyzed]] reactions as described below in the section on organic chemistry.<ref name="UllmannFe" />

In terms of its being an oxidant, iron(III) chloride oxidizes iron powder to form iron(II) chloride via a [[comproportionation]] reaction:<ref name=UllmannFe/>

:{{chem2|2 FeCl3 + Fe → 3 FeCl2}}

A traditional synthesis of anhydrous [[ferrous chloride]] is the reduction of [[ferric chloride|FeCl₃]] with [[chlorobenzene]]:<ref>{{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 }}</ref>

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

iron(III) chloride releases chlorine gas when heated above 160&nbsp;°C, generating [[ferrous chloride]]:<ref name=Brauer/>

:{{chem2|2FeCl3 → 2FeCl2 + Cl2}}

To suppress this reaction, the preparation of iron(III) chloride requires an excess of chlorinating agent, as discussed above.<ref name=Brauer/><ref name="UllmannFe" />

===Hydrated FeCl₃===

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).

Like the anhydrous material, hydrated ferric chloride is oxophilic. For example, [[Oxalic acid|oxalate]] salts react rapidly with aqueous iron(III) chloride to give {{Chem2|[Fe(C2O4)3](3−)}}, known as [[ferrioxalate]]. Other [[carboxylate]] sources, e.g., [[Citric acid|citrate]] and [[tartaric acid|tartrate]], bind as well to give [[carboxylate complex]]es. 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.<ref>{{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]]/[[John Wiley & Sons|Wiley]]|year=1989|isbn=9780582462366|edition=5th|location=New York|display-authors=3}}</ref> The affinity of iron(III) for phenols is exploited in the [[Trinder spot test]].<ref>{{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}}</ref>

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.

===Organometallic chemistry===

The interaction of anhydrous iron(III) chloride with [[organolithium]] and [[organomagnesium compound]]s 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 agent]]s. Such studies may be relevant to the mechanism of FeCl₃-catalyzed [[cross-coupling reaction]]s.<ref name=Byers>{{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 }}</ref> 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.<ref>{{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.</ref> Illustrating the sensitivity of these reactions, [[methyl lithium]] {{Chem2|LiCH3}} reacts with iron(III) chloride to give lithium [[tetrachloroferrate]](II) {{Chem2|Li2[FeCl4]}}:<ref>{{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=[[Zeitschrift für anorganische und allgemeine Chemie|Z. Anorg. Allg. Chem.]]|language=de|volume=391|issue=3|pages=193–202|doi=10.1002/zaac.19723910302}}</ref>

:{{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.<ref name=EROS/> These diketonate complexes have the advantages that they do not form hydrates, unlike iron(III) chloride, and they are more soluble in relevant solvents.<ref name=Byers/>

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

:{{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.<ref name = Pauson2001>{{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}}</ref>

==Uses==

=== Water treatment===

In the largest application iron(III) chloride is in [[sewage treatment]] and [[water treatment|drinking water production]]. By forming highly dispersed networks of Fe-O-Fe containing materials, ferric chlorides serve as coagulant and flocculants.<ref name="wtcbrochure">{{cite book|url=http://www.akzonobel.com/ic/system/images/AkzoNobel_WTCBrochureENG_tcm18-9982.pdf|title=Water Treatment Chemicals|publisher=[[Akzo Nobel|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}}</ref> In this application, an aqueous solution of {{Chem2|FeCl3}} is treated with base to form a [[Flocculation|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.<ref name=UllmannFe>{{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 }}</ref>

Iron(III) chloride is also used to remove soluble [[phosphate]] from wastewater. [[Iron(III) phosphate]] is [[insoluble]] and thus precipitates as a solid.<ref>{{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]] }}</ref> One potential advantage to its use in water treatment, ferric ion oxidizes (deodorizes) [[hydrogen sulfide]].<ref>{{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 }}</ref>

===Etching and metal cleaning===

It is also used as a [[Leaching (chemistry)|leaching]] agent in chloride hydrometallurgy,<ref>{{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}}</ref> for example in the production of Si from FeSi (Silgrain process by [[Elkem]]).<ref>{{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=[[Chemical Engineering Science|Chem. Eng. Sci.]]|volume=61|issue=1|pages=229–245|doi=10.1016/j.ces.2005.01.047|bibcode=2006ChEnS..61..229D }}</ref>

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).<ref name="greenwood">{{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}}</ref>

Iron(III) chloride is used in many other hobbies involving metallic objects.<ref>{{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}}</ref><ref>{{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}}</ref><ref>{{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}}</ref><ref>{{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}}</ref><ref>{{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 }}</ref>

===Organic chemistry===

[[File:UJIMUV.jpg|thumb|Structure of FeCl₃(diethylether)₂. Color code: Cl=green,Fe = blue, O = red.|left]]

In industry, iron(III) chloride is used as a catalyst for the reaction of [[ethylene]] with [[chlorine]], forming ethylene dichloride ([[1,2-dichloroethane]]):<ref>{{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 }}</ref>

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

Ethylene dichloride is a [[Commodity chemicals|commodity chemical]], which is mainly used for the industrial production of [[vinyl chloride]], the [[monomer]] for making [[polyvinyl chloride|PVC]].<ref>{{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}}</ref>

Illustrating it use as a [[Lewis acid]], iron(III) chloride [[catalyst|catalyses]] [[electrophilic aromatic substitution]] and [[chlorination reaction|chlorination]]s. In this role, its function is similar to that of [[aluminium chloride]]. In some cases, mixtures of the two are used.<ref>{{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 }}</ref>

====Organic synthesis research====

Although iron(III) chlorides are seldom used in practical [[organic synthesis]], they have received considerable attention as [[reagent]]s because they are inexpensive, earth abundant, and relatively nontoxic. Many experiments probe both its redox activity and its Lewis acidity.<ref name=EROS/> For example, iron(III) chloride oxidizes naphthols to naphthoquinones:<ref name=EROS/><ref>{{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 }}</ref> 3-Alkyl[[thiophene]]s are polymerized to [[polythiophene]]s upon treatment with ferric chloride.<ref>{{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 }}</ref> Iron(III) chloride has been shown to promote C-C [[coupling reaction]].<ref>{{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 }}</ref>

Several reagents have been developed based on [[catalyst support|supported]] iron(III) chloride. On [[silica gel]], the anhydrous salt has been applied to certain [[Dehydration reaction|dehydration]] and [[pinacol rearrangement|pinacol-type rearrangement]] reactions. A similar reagent but moistened induces hydrolysis or [[epimerization]] reactions.<ref>{{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 }}</ref> On [[alumina]], ferric chloride has been shown to accelerate [[ene reaction]]s.<ref>{{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 }}</ref>

<!--Ferric chloride in conjunction with [[Sodium iodide|NaI]] in [[acetonitrile]] solution reduces organic [[azide]]s to primary [[amine]]s.<ref>{{cite journal|display-authors=3|vauthors=Kamal A, Ramana K, Ankati H, Ramana A|year=2002|title=Mild and efficient reduction of azides to amines: synthesis of fused [2,1-''b'']quinazolines|journal=[[Tetrahedron Letters|Tetrahedron Lett.]]|volume=43|issue=38|pages=6861–6863|doi=10.1016/S0040-4039(02)01454-5}}</ref>-->

When pretreated with [[sodium hydride]], iron(III) chloride gives a hydride [[reducing agent]] that convert [[alkene]]s and [[ketone]]s into [[alkane]]s and [[Alcohol (chemistry)|alcohol]]s, respectively.<ref>{{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 }}</ref>

[[File:FeCl3oxidation.svg|center|386px]]

=== Histology===

<!--* Used in veterinary practice to treat overcropping of an animal's claws, particularly when the overcropping results in bleeding{{cn|date=January 2023}}

* Used in an animal thrombosis model.<ref>{{cite journal|display-authors=3|vauthors=Tseng M, Dozier A, Haribabu B, Graham UM|year=2006|title=Transendothelial migration of ferric ion in FeCl₃ injured murine common carotid artery|journal=[[Thrombosis Research|Thromb. Res.]]|volume=118|issue=2|pages=275–280|doi=10.1016/j.thromres.2005.09.004|pmid=16243382}}</ref>

* -->Iron(III) chloride is a component of useful stains, such as [[Carnoy's solution]], a [[Fixation (histology)|histological fixative]] with many applications. Also, it is used to prepare [[Verhoeff's stain]].<ref name="ucdavis">{{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, [[University of California, Davis|U.C. Davis]] | access-date =2 January 2013 }}</ref>

==Natural occurrence==

Like many metal halides, {{chem2|FeCl3}} naturally occurs as a trace mineral. The rare mineral '''molysite''' is usually associated with [[volcano]]es and [[fumarole]]s.<ref>{{cite web |title=Molysite |url=https://www.mindat.org/min-2749.html |website=mindat.org |publisher=Mindat |access-date=5 February 2024}}</ref><ref name="IMA">{{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}}</ref>

{{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|Atmospheric Methane Removal]].<ref>{{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}}</ref>

The clouds of [[Venus]] are hypothesized to contain approximately 1% {{chem2|FeCl3}} dissolved in [[sulfuric acid]].<ref name="kras006">{{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 }}</ref><ref>{{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}}</ref>

== Safety ==

Iron(III) chlorides are widely used in the [[water treatment|treatment of drinking water]],<ref name="UllmannFe" /> 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|[[Iron|Fe]][[chloride|Cl]]3}} aqueous solution, is highly [[Corrosive substance|corrosive]], and must be handled using proper protective equipment.<ref name=EROS>{{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 }}</ref>

==Notes==

{{reflist|group=Note}}

==References==

{{reflist|30em}}

==Further reading==

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

#{{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}}

#{{Cite book|title=The Merck Index of Chemicals and Drugs|publisher=Merck & Co|year=1960|veditors=Stecher PG, Finkel MJ, Siegmund OH|edition=7th|location=Rahway, New Jersey, US}}

#{{Cite book|title=Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.|vauthors=Nicholls D|publisher=Macmillan Press|year=1974|isbn=9780333170885|series=A Macmillan chemistry text|location=London}}

#{{Cite book|title=Structural Inorganic Chemistry|vauthors=Wells AF|publisher=Oxford University Press|year=1984|isbn=9780198553700|edition=5th|series=Oxford science publications|location=Oxford, UK}}

#{{Cite book|title=Acidic and Basic Reagents|publisher=John Wiley & Sons, Inc.|year=1999|isbn=9780471979258|veditors=Reich HJ, Rigby HJ|series=Handbook of Reagents for Organic Synthesis|location=New York}}

{{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]]