Iron(III) chloride

Iron(III) chloride


IUPAC name Iron(III) chloride Iron trichloride
Other names Ferric chloride Molysite Flores martis
Identifiers
CAS number	7705-08-0^Y, 10025-77-1 (hexahydrate)
PubChem	24380
ChemSpider	22792^Y
UN number	1773 (anhydrous) 2582 (aq. soln.)
ChEBI	CHEBI:30808^Y
RTECS number	LJ9100000
Jmol-3D images	Image 1
SMILES Cl[Fe](Cl)Cl
InChI InChI=1S/3ClH.Fe/h3*1H;/q;;;+3/p-3^Y Key: RBTARNINKXHZNM-UHFFFAOYSA-K^Y
Properties
Molecular formula	FeCl₃
Molar mass	162.2 g/mol (anhydrous) 270.3 g/mol (hexahydrate)
Appearance	green-black by reflected light; purple-red by transmitted light hexahydrate: yellow solid aq. solutions: brown
Density	2.898 g/cm³ (anhydrous)
Melting point	306 °C (anhydrous) 37 °C (hexahydrate)
Boiling point	315 °C (anhydrous, decomp) 280 °C (hexahydrate, decomp) (partial decomposition to FeCl₂ + Cl₂)
Solubility in water	74.4 g/100 mL (0 °C) ^[1] 92 g/100 mL (hexahydrate, 20 °C)
Solubility in acetone Methanol Ethanol Diethyl ether	63 g/100 ml (18 °C) highly soluble 83 g/100 ml highly soluble
Viscosity	40% solution: 12 cP
Structure
Crystal structure	hexagonal
Coordination geometry	octahedral
Hazards^[2]^[3]^{[Note 1]}
MSDS	ICSC 1499
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H290, H302, H314, H318
GHS precautionary statements	P234, P260, P264, P270, P273, P280, P301+312, P301+330+331, P303+361+353, P363, P304+340, P310, P321, P305+351+338
EU Index	not listed
NFPA 704	0 2 0
Flash point	non-flammable
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 coagulants	Iron(II) sulfate Polyaluminium chloride
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Iron(III) chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula Fe Cl₃. The colour of iron(III) chloride crystals 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 is deliquescent, forming hydrated hydrogen chloride mists in moist air. It is rarely observed in its natural form, mineral molysite, known mainly from some fumaroles.

When dissolved in water, iron(III) chloride undergoes hydrolysis and gives off heat in an exothermic reaction. The resulting brown, acidic, and corrosive solution is used as a flocculent in sewage treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron(III) chloride is a fairly strong Lewis acid, and it is used as a catalyst in organic synthesis.

1 Structure and properties
2 Preparation
3 Reactions
- 3.1 Oxidization
4 Uses
5 Safety
6 See also
7 Notes and references
- 7.1 Notes
- 7.2 References
8 Further reading

Structure and properties

Iron(III) chloride adopts the BiI₃ structure, which features 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 vapour consists of the dimer Fe₂Cl₆ (c.f. aluminium chloride) which increasingly dissociates into the monomeric FeCl₃ (D_3h point group molecular symmetry) at higher temperature, in competition with its reversible decomposition to give iron(II) chloride and chlorine gas.^[5]

Preparation

Anhydrous iron(III) chloride may be prepared by union of the elements:^[6]

2 Fe(s) + 3 Cl₂(g) → 2 FeCl₃(s)

Solutions of iron(III) chloride are produced industrially both from iron and from ore, in a closed-loop process.

Dissolving pure iron in a solution of iron(III) chloride

Fe(s) + 2 FeCl₃(aq) → 3 FeCl₂(aq)
Dissolving iron ore in hydrochloric acid

Fe₃O₄(s) + 8 HCl(aq) → FeCl₂(aq) + 2 FeCl₃(aq) + 4 H₂O
Oxidation of iron (II) chloride with chlorine

2 FeCl₂(aq) + Cl₂(g) → 2 FeCl₃(aq)

Like many other hydrated metal chlorides, hydrated iron(III) chloride can be converted to the anhydrous salt by refluxing with thionyl chloride.^[7] The hydrate cannot be converted to anhydrous iron(III) chloride by only heat, as instead HCl is evolved and iron oxychloride forms.

Reactions

Iron(III) chloride undergoes hydrolysis to give an acidic solution. When heated with iron(III) oxide at 350 °C, iron(III) chloride gives iron oxychloride, a layered solid and intercalation host.

FeCl₃ + Fe₂O₃ → 3 FeOCl

It is a moderately strong Lewis acid, forming adducts with Lewis bases such as triphenylphosphine oxide, e.g. FeCl₃(OPPh₃)₂ where Ph = 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.

Alkali metal alkoxides react to give the metal alkoxide complexes of varying complexity.^[8] The compounds can be dimeric or trimeric.^[9] In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl₃ and sodium ethoxide:^[10]^[11]

FeCl₃ + 3 [C₂H₅O]^-Na⁺ → Fe(OC₂H₅)₃ + 3 NaCl

Oxalates react rapidly with aqueous iron(III) chloride to give [Fe(C₂O₄)₃]³⁻. Other carboxylate salts form complexes, e.g. citrate and tartrate.

Oxidization

Iron(III) chloride is a mild oxidising agent, for example, it is capable of oxidising copper(I) chloride to copper(II) chloride.

FeCl₃ + CuCl → FeCl₂ + CuCl₂

It also reacts with iron to form iron(II) chloride:

2 FeCl₃ + Fe → 3 FeCl₂

Reducing agents such as hydrazine convert iron(III) chloride to complexes of iron(II).

Uses

Industrial

In industrial application, iron(III) chloride is used in sewage treatment and drinking water production.^[12] 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.

Fe³⁺ + 4 OH⁻ → Fe(OH)₄⁻ → FeO(OH)₂⁻·H₂O

It is also used as a leaching agent in chloride hydrometallurgy,^[13] for example in the production of Si from FeSi. (Silgrain process)^[14]

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.^[15]

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 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.^[16] 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.

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.

Other uses

Used in anhydrous form as a drying reagent in certain reactions.
Used in water and wastewater treatment to precipitate phosphate as iron (III) phosphate.
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 knife craftsmen and sword smiths to stain blades, as to give a contrasting effect to the metal, and 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).
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.^[17]
Sometimes used in the technique of Raku firing as an additive during the reduction process, turning a pottery piece a burnt orange color due to the iron content present in the reducing atmosphere.
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.^[18]
Used in an animal thrombosis model ^[19]

Safety

Iron(III) chloride is toxic, highly corrosive and acidic. The anhydrous material is a powerful dehydrating agent.

Notes and references

Notes

^ An alternative GHS classification from the Japanese GHS Inter-ministerial Committee (2006)^[4] notes the possibility of respiratory tract irritation from FeCl₃ and differs slightly in other respects from the classification used here.

References

^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
^ HSNO Chemical Classification Information Database (New Zealand Environmental Risk Management Authority), http://www.ermanz.govt.nz/Chemicals/ChemicalDisplay.aspx?SubstanceID=10764, retrieved 2010-09-19
^ Various suppliers, collated by the Baylor College of Dentistry, Texas A&M University. (accessed 2010-09-19)
^ , Japanese GHS Inter-ministerial Committee, 2006, http://www.safe.nite.go.jp/english/ghs_index.html#results, retrieved 2010-09-19
^ Holleman, A.F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
^ Tarr, B.R.; Booth, Harold S.; Dolance, Albert (1950). "Anhydrous Iron(III) Chloride". Inorganic Syntheses. Inorganic Syntheses 3: 191–194. doi:10.1002/9780470132340.ch51. ISBN 9780470132340.
^ Pray, Alfred R.; Richard F. Heitmiller, Stanley Strycker (1990). "Anhydrous Metal Chlorides". Inorganic Syntheses. Inorganic Syntheses 28: 321–323. doi:10.1002/9780470132593.ch80. ISBN 9780470132593.
^ The chemistry of metal alkoxides, Nataliya Ya Turova , 12.22.1 'Synthesis' , p.481 google books link
^ Alkoxo and aryloxo derivatives of metals By D. C. Bradley , 3.2.10 , Alkoxides of later 3d metals , p69 google books links
^ Fe9O3(OC2H5)21·C2H5OH — A New Structure Type of an Uncharged Iron(III) Oxide-Alkoxide Cluster , Michael Veith, Frank Grätz, Volker Huch , European Journal of Inorganic Chemistry , Vol 2001, Issue 2, pp.367-368 online link
^ The synthesis of iron (III) ethoxide revisited: Characterization of the metathesis products of iron (III) halides and sodium ethoxide , Gulaim A. Seisenbaevaa, Suresh Gohila, Evgeniya V. Suslovab, Tatiana V. Rogovab, Nataliya Ya. Turovab, Vadim G. Kesslera , Inorganica Chimica Acta , Volume 358, Issue 12, 1/8/2005, pp.3506-3512 , online link
^ (PDF) Water Treatment Chemicals. Akzo Nobel Base Chemicals. 2007. http://www.akzonobel.com/ic/system/images/AkzoNobel_WTCBrochureENG_tcm18-9982.pdf. Retrieved 2007-10-26.
^ Separation and Purification Technology 51 (2006) pp 332-337
^ Chem. Eng. Sci. 61 (2006) pp 229-245
^ Greenwood, N.N.; A. Earnshaw (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann.
^ Furnell, B.S.; et al. (1989). Vogel's Textbook of Practical Organic Chemistry (5th ed.). New York: Longman/Wiley.
^ Kealy, T.J.; Pauson, P. L. (1951). "A New Type of Organo-Iron Compound". Nature 168 (4285): 1040. doi:10.1038/1681039b0.
^ Kamal, Ahmed; Ramana, K; Ankati, H; Ramana, A (2002). "Mild and efficient reduction of azides to amines: synthesis of fused [2,1-b]quinazolines". Tetrahedron Letters 43 (38): 6961. doi:10.1016/S0040-4039(02)01454-5.
^ Tseng, Michael; Dozier, A; Haribabu, B; Graham, UM (2006). "Transendothelial migration of ferric ion in FeCl3 injured murine common carotid artery". Thrombosis Research 118 (2): 275–280. doi:10.1016/j.thromres.2005.09.004. PMID 16243382.