Iron(III) chloride Iron(III) chloride is the inorganic compound with the Iron(III) chloride 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. Contents Structure and properties Anhydrous Iron(III) chloride (hydrate) Hydrates Aqueous solution Preparation Reactions Redox reactions With carboxylate anions With alkali metal alkoxides With organometallic compounds Uses Industrial Laboratory use Other uses Safety Iron(III) chloride (anhydrous) Natural occurrence See also Notes References Further reading Names IUPAC names Iron(III) chloride Structure and properties Iron trichloride Other names Anhydrous Ferric chloride Molysite Anhydrous iron(III) chloride has the BiI structure, with 3 Flores martis octahedral Fe(III) centres interconnected by two-coordinate chloride ligands.[3] Identifiers CAS Number 7705-08-0 (http://www.c Iron(III) chloride has a relatively low melting point and boils ommonchemistry.org/Ch at around 315 °C. The vapour consists of the dimer Fe Cl (cf. 2 6 emicalDetail.aspx?ref=7 aluminium chloride) which increasingly dissociates into the 705-08-0) monomeric FeCl3 (with D3h point group molecular 10025-77-1 (http://www. symmetry) at higher temperature, in competition with its commonchemistry.org/C reversible decomposition to give iron(II) chloride and hemicalDetail.aspx?ref= [8] chlorine gas. 10025-77-1) (hexahydrate) Hydrates 54862-84-9 (http://www. commonchemistry.org/C In addition to the anhydrous material, ferric chloride forms hemicalDetail.aspx?ref= four hydrates. All forms of iron(III) chloride feature two or 54862-84-9) (dihydrate) more chlorides as ligands, and three hydrates feature 64333-00-2 (http://www. FeCl −.[9] 4 commonchemistry.org/C hemicalDetail.aspx?ref= hexahydrate: FeCl .6H O has the structural formula 3 2 64333-00-2) trans-[Fe(H O) Cl ]Cl.2H O[10] 2 4 2 2 (3.5hydrate) . FeCl3 2.5H O has the structural formula cis-[Fe(H2O)4Cl2] 2 3D model (JSmol) Interactive image (http [FeCl ].H O. 4 2 s://chemapps.stolaf.edu/ . dihydrate: FeCl3 2H2O has the structural formula trans- jmol/jmol.php?model=C [Fe(H2O)4Cl2][FeCl4]. l%5BFe%5D%28Cl%29 . FeCl3 3.5H2O has the structural formula cis- Cl) [FeCl (H O) ][FeCl ].3H O. 2 2 4 4 2 ChEBI CHEBI:30808 (https://w ww.ebi.ac.uk/chebi/sear Aqueous solution chId.do? chebiId=30808) Aqueous solutions of ferric chloride are characteristically ChemSpider 22792 (http://www.chem 3+ yellow, in contrast to the pale pink solutions of [Fe(H2O)6] . spider.com/Chemical-St According to spectroscopic measurements, the main species ructure.22792.html) in aqueous solutions of ferric chloride are the octahedral + ECHA InfoCard 100.028.846 (https://ech complex [FeCl2(H2O)4] (stereochemistry unspecified) and − [9] a.europa.eu/substance-i the tetrahedral [FeCl4] . nformation/-/substancei nfo/100.028.846) Preparation EC Number 231-729-4 Anhydrous iron(III) chloride may be prepared by union of PubChem CID 24380 (https://pubchem. [11] the elements: ncbi.nlm.nih.gov/compo und/24380) RTECS number LJ9100000 Solutions of iron(III) chloride are produced industrially both UNII U38V3ZVV3V (https://fd from iron and from ore, in a closed-loop process. asis.nlm.nih.gov/srs/srs 1. Dissolving iron ore in hydrochloric acid direct.jsp?regno=U38V3 ZVV3V) 0I2XIN602U (https://fda sis.nlm.nih.gov/srs/srsdi rect.jsp?regno=0I2XIN6 02U) (hexahydrate) UN number 1773 (anhydrous) 2582 (aq. soln.) DTXSID8020622 (http CompTox s://comptox.epa.gov/das Dashboard (EPA) hboard/DTXSID802062 2) InChI InChI=1S/3ClH.Fe/h3*1H;/q;;;+3/p-3 Key: RBTARNINKXHZNM-UHFFFAOYSA-K InChI=1S/3ClH.Fe/h3*1H;/q;;;+3/p-3 Key: RBTARNINKXHZNM-DFZHHIFOAF Key: RBTARNINKXHZNM-UHFFFAOYSA-K SMILES Cl[Fe](Cl)Cl Properties Chemical formula FeCl3 Molar mass 162.204 g/mol (anhydrous) 270.295 g/mol (hexahydrate)[1] Appearance Green-black by reflected light; purple- red by transmitted light; yellow solid as hexahydrate; brown as aq. solution Odor Slight HCl Density 2.90 g/cm3 (anhydrous) 1.82 g/cm3 (hexahydrate)[1] Melting point 307.6 °C (585.7 °F; 580.8 K) (anhydrous) 37 °C (99 °F; 310 K) (hexahydrate)[1] Boiling point 316 °C (601 °F; 589 K) (anhydrous, decomposes)[1] 280 °C (536 °F; 553 K) (hexahydrate, decomposes) Solubility in water 912 g/L (anh. or hexahydrate, 25 °C)[1] Solubility in Acetone 630 g/L (18 °C) Methanol Highly soluble Ethanol 830 g/L [1] Diethyl ether Highly soluble +13,450·10−6 cm3/mol[2] Magnetic susceptibility (χ) Viscosity 12 cP (40% solution) Structure Crystal 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 Octahedral geometry Hazards[5][6][Note 1] Safety data sheet ICSC 1499 (http://www.i nchem.org/documents/i csc/icsc/eics1499.htm) GHS pictograms GHS Signal word Danger GHS hazard H290, H302, H314, statements H318 GHS P234, P260, P264, precautionary P270, P273, P280, statements P301+312, P301+330+331, P303+361+353, P363, P304+340, P310, P321, P305+351+338, P390, P405, P406, P501 NFPA 704 (fire diamond) 0 2 0 Flash point Non-flammable NIOSH (US health exposure limits): REL TWA 1 mg/m3[4] (Recommended) Related compounds Other anions Iron(III) fluoride Iron(III) bromide Other cations Iron(II) chloride Manganese(II) chloride Cobalt(II) chloride Ruthenium(III) chloride Related Iron(II) sulfate coagulants Polyaluminium chloride Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references 2. Oxidation of iron(II) chloride with chlorine 3. Oxidation of iron(II) chloride with oxygen Small amounts can be produced by reacting iron with hydrochloric acid, then with hydrogen peroxide. The hydrogen peroxide is the oxidant in turning ferrous chloride into ferric chloride Anhydrous iron(III) chloride cannot be obtained from the hydrate by heating. Instead, the solid decomposes into HCl and iron oxychloride. The conversion can be accomplished by treatment with thionyl chloride.[12] Similarly, dehydration can be effected with trimethylsilyl chloride:[13] Reactions Iron(III) chloride undergoes hydrolysis to give a strongly acidic solution.[14][9] When heated with iron(III) oxide at 350 °C, iron(III) chloride gives iron oxychloride, a layered solid and intercalation host.[15] The anhydrous salt is a moderately strong Lewis acid, forming adducts with Lewis bases such as triphenylphosphine oxide; e.g., A brown, acidic solution of iron(III) FeCl3(OPPh3)2 where Ph is phenyl. It also reacts with other chloride − − 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 oxidising agent, for example, it is capable of oxidising copper(I) chloride to copper(II) chloride. It also reacts with iron to form iron(II) chloride: [16] A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene: With carboxylate anions 3− Oxalates react rapidly with aqueous iron(III) chloride to give [Fe(C2O4)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 [19][20] been described for the nominal stoichiometric reaction between FeCl3 and sodium ethoxide: With organometallic compounds Iron(III) chloride in ether solution oxidizes methyl lithium LiCH3 to give first light greenish yellow lithium tetrachloroferrate(III) LiFeCl4 solution and then, with further addition of methyl lithium, [21][22] lithium tetrachloroferrate(II) Li2FeCl4: 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 [23] flocculant. In this application, FeCl3 in slightly basic water reacts with the hydroxide ion to form a floc of iron(III) hydroxide, or more precisely formulated as FeO(OH)− , that can remove suspended materials. It is also used as a leaching agent in chloride hydrometallurgy,[24] for example in the production of Si from FeSi (Silgrain process).[25] 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.[26] 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. Laboratory use In the laboratory iron(III) chloride is commonly employed as a Lewis acid for catalysing reactions such as chlorination of aromatic compounds and Friedel–Crafts reaction of aromatics. It is less powerful than aluminium 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 neutralised with sodium hydroxide until a slight precipitate of FeO(OH) is formed.[27] The mixture is filtered before use. The organic substance is dissolved in water, methanol or ethanol, then the neutralised iron(III) chloride solution is added—a transient or permanent coloration (usually purple, green or blue) indicates the presence of a phenol or enol.