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Iron(III) chloride

Iron(III) chloride (anhydrous) Iron(III) chloride (hydrate)
Names
IUPAC names Iron(III) chloride Iron trichloride
Other names Ferric chloride Molysite Flores martis
Identifiers
CAS Number	7705-08-0  10025-77-1 (hexahydrate)  54862-84-9 (dihydrate)  64333-00-2 (3.5hydrate)
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30808
ChemSpider	22792
ECHA InfoCard	100.028.846
EC Number	231-729-4
PubChem CID	24380
RTECS number	LJ9100000
UNII	U38V3ZVV3V  0I2XIN602U (hexahydrate)  Y048945596 (dihydrate)
UN number	1773 (anhydrous) 2582 (aqueous solution)
CompTox Dashboard (EPA)	DTXSID8020622
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 aqueous 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 (anhydrous or hexahydrate, 25 °C)[1]
Solubility in Acetone Methanol Ethanol Diethyl ether[1]	630 g/L (18 °C) Highly soluble 830 g/L Highly soluble
Magnetic susceptibility (χ)	+13,450·10−6 cm3/mol[2]
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 geometry	Octahedral
Hazards[5][6][Note 1]
GHS labelling:
Pictograms
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)	2 0 0
Flash point	Non-flammable
NIOSH (US health exposure limits):
REL (Recommended)	TWA 1 mg/m3[4]
Safety data sheet (SDS)	ICSC 1499
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
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

Iron(III) chloride describes the inorganic compounds with the formula FeCl₃(H₂O)_x. Also called ferric chloride, these compounds are available both in an anhydrous and hydrated forms. They are common source of iron in the +3 oxidation state. The hydrate and the anhydrous derivative have distinct properties.

Structure and properties[edit]

All forms of ferric chloride are paramagnetic, owing to the presence of five unpaired electrons residing in 3d orbitals. This electronic configuration places electrons in molecular orbitals that are antibonding with respect to ligands. Thus, iron(III) chlorides are labile, undergoing rapid ligand exchange in solution. In contrast to their kinetic lability, iron(III) chlorides are thermodynamically robust, as reflected by the vigorous methods applied to their synthesis.

Anhydrous[edit]

The anhydrous compound is a 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 BiI₃ structure, with octahedral Fe(III) centres 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 D_3h point group molecular symmetry) at higher temperature, in competition with its reversible decomposition to give iron(II) chloride and chlorine gas.^[8]

Hydrates[edit]

In addition to the anhydrous material, ferric chloride aggressively forms hydrates upon exposure to water, reflecting its Lewis acidity. Four of these hydrates have been crystallized and examined by X-ray crystallography. They all feature trans—[FeCl₂(H₂O)₄]⁺ cations, with either chloride or [FeCl₄]⁻ as the anions.^[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]

Solution[edit]

Aqueous solutions of ferric chloride are characteristically yellow, in contrast to the pale pink solutions of [Fe(H₂O)₆]³⁺. Thus, the chloride ligand significantly influences the optical properties of the iron center. According to spectroscopic measurements, the main species in aqueous solutions of ferric chloride are the octahedral [FeCl₂(H₂O)₄]⁺ (stereochemistry unspecified) and the tetrahedral [FeCl₄]⁻.^[9] The cationic aquo complex is strongly acidic:^[11][9]

[FeCl₂(H₂O)₄)]⁺ ⇌ [FeCl₂(OH)(H₂O)₃] + H⁺

Anhydrous iron(III) chloride dissolves in diethyl ether and tetrahydrofuran forming 1:2 adducts of the formula FeCl₃(ether)₂. In these complexes, the iron is pentacoordinate.^[12]

Preparation[edit]

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

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.^[13] A similar but laboratory scale process also has been described.^[14]

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

1. Dissolving iron ore in hydrochloric acid

   Fe₃O₄ + 8 HCl → FeCl₂ + 2 FeCl₃ + 4 H₂O

2. Oxidation of iron(II) chloride with chlorine

   2 FeCl₂ + Cl₂ → 2 FeCl₃

3. 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.^[15] Similarly, dehydration can be effected with trimethylsilyl chloride:^[16]

FeCl₃·6H₂O + 12 (CH₃)₃SiCl → FeCl₃ + 6 ((CH₃)₃Si)₂O + 12 HCl

Reactions[edit]

The reactivity of ferric chloride reveals two trends: It is a Lewis acid and an oxidizing agent.

Lewis-acid reactions[edit]

Reactions of iron(III) chlorides reflect the description of iron(III) as oxophilic and a hard Lewis acid. The rapidity of these reactions are consistent with the lability of ferric ion, reflecting its typical high-spin electronic configuration. Thus, oxalate salts react rapidly with aqueous iron(III) chloride to give [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 superceded by spectroscopic methods, the ferric chloride test is a traditional colorimetric test.^[17] The affinity of iron(III) for phenols is exploited in the Trinder spot test.

Myriad other manifestation of the oxophiliicty of iron(III) chloride are available. When heated with iron(III) oxide at 350 °C it reactions to give iron oxychloride:^[18]

FeCl₃ + Fe₂O₃ → 3FeOCl

Alkali metal alkoxides react to give the iron(III) alkoxide complexes. These products have more complicated structures that the anhydrous iron(III) chloride.^[19][20] In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl₃ and sodium ethoxide:

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., FeCl₃(OP(C₆H₅)₃)₂. The related 1:2 complex , has been crystallized from ether solution.^[12]

Iron(III) chloride also reacts with tetraethylammonium chloride to give the yellow salt of the tetrachloroferrate ion ((Et₄N)[FeCl₄]). Similarly combining FeCl₃ with NaCl and KCl gives Na[FeCl₄] and K[FeCl₄], respectively.^[21]

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.

Redox reactions[edit]

Iron(III) chloride is a mild oxidizing agent. It serves as one-electron oxidant illustrated by its reaction with copper(I) chloride to give copper(II) chloride and iron(II) chloride.

FeCl₃ + CuCl → FeCl₂ + CuCl₂

In a comproportionation reaction, iron(III) chloride reacts with iron powder to form iron(II) chloride:^[13]

2 FeCl₃ + Fe → 3 FeCl₂

A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl₃ with chlorobenzene:^[22]

2 FeCl₃ + C₆H₅Cl → 2 FeCl₂ + C₆H₄Cl₂ + HCl

Organometallic chemistry[edit]

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 etherial solvents, which are compatible with the nucleophilic alkylating agents. Such studies may be relevant to the mechanism of FeCl₃-catalyzed cross coupling reactions.^[23] 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.^[24] Illustrating the sensitivity of these reactions, methyl lithium LiCH₃ reacts with iron(III) chloride to give lithium tetrachloroferrate(II) Li₂[FeCl₄]:^[25]

2 FeCl₃ + LiCH₃ → FeCl₂ + Li[FeCl₄] + 0.5 CH₃CH₃

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.^[26] These diketonate complexes have the advantages that they do not form hydrates, unlike iron(III) chloride, and they are more soluble in relevant solvents.^[23]
Cyclopentadienyl magnesium bromide undergoes a complex reaction with iron(III) chloride, resulting in ferrocene:^[27]

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.^[28]

Uses[edit]

Water treatment[edit]

In the largest application iron(III) chloride is used in sewage treatment and drinking water production as a coagulant and flocculant.^[29] In this application, an aqueous solution of FeCl₃ is treated with base to form a floc of iron(III) hydroxide (Fe(OH)₃), also formulated as FeO(OH) (ferrihydrite). This floc facilitates the separation of suspended materials, clarifying the water.^[13]

Iron(III) chloride is also used to remove soluble phosphate from wastewater. Iron(III) phosphate is insoluble and thus precipitates as a solid.^[30] One potential advantage to its use in water treatment, ferric ion oxidizes (deodorizes) hydrogen sulfide.^[31]

Etching and metal cleaning[edit]

It is also used as a leaching agent in chloride hydrometallurgy,^[32] for example in the production of Si from FeSi (Silgrain process by Elkem).^[33]

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

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).^[34]

Iron(III) chloride is used in many other hobbies involving metallic objects.^{[35][36][37][38][39]}

Organic chemistry[edit]

In industry, iron(III) chloride is used as catalyst for the reaction of ethylene with chlorine, forming ethylene dichloride (1,2-dichloroethane):^[40]

H₂C=CH₂ + Cl₂ → ClCH₂CH₂Cl

Ethylene dichloride is a commodity chemical, which is mainly used for the industrial production of vinyl chloride, the monomer for making PVC.

Several reagents for organic synthesis have been developed based especially on anhydrous iron(III) chloride:

• Ferric chloride on silica gel is a reagent that has high reactivity towards several oxygen-containing functional groups. When the reagent is dry, its acidity and high affinity for water lead to dehydration and pinacol-type rearrangement reactions. When the reagent is moistened, it instead induces hydrolysis or epimerization reactions.^[41]
• Ferric chloride on alumina is used to accelerate ene reactions.^[42]
• Ferric chloride in conjunction with NaI in acetonitrile solution reduces organic azides to primary amines.^[43]
• When mixed with sodium hydride, iron(III) chloride gives a hydride reducing agent. This reagent has been shown to convert alkenes and ketones into alkanes and alcohols, respectfully.^[44]

As a reagent in organic chemistry, iron(III) chloride has attracted interest for both its redox activity and its Lewis acidity. Furthermore, because they are inexpensive and relatively nontoxic, iron chlorides have been widely examined.^[26] 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.^[45] Iron(III) chloride oxidizes naphthols to naphthoquinones:^[26][46]

Histology[edit]

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.

Safety[edit]

Anhydrous iron(III) chloride is harmful, highly corrosive, and acidic.^[26]

Natural occurrence[edit]

The natural counterpart of FeCl₃ is the rare mineral molysite, usually related to volcanic and other-type fumaroles.^[47][48]

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.^[49]

The clouds of Venus are hypothesized to contain approximately 1% FeCl₃ dissolved in sulfuric acid.^[50][51]

Notes[edit]

References[edit]

Further reading[edit]

1. Lide DR, ed. (1990). CRC Handbook of Chemistry and Physics (71st ed.). Ann Arbor, MI, USA: CRC Press. ISBN 9780849304712.
2. Stecher PG, Finkel MJ, Siegmund OH, eds. (1960). The Merck Index of Chemicals and Drugs (7th ed.). Rahway, NJ, USA: Merck & Co.
3. Nicholls D (1974). Complexes and First-Row Transition Elements, Macmillan Press, London, 1973. A Macmillan chemistry text. London: Macmillan Press. ISBN 9780333170885.
4. Wells AF (1984). Structural Inorganic Chemistry. Oxford science publications (5th ed.). Oxford, UK: Oxford University Press. ISBN 9780198553700.
5. Reich HJ, Rigby HJ, eds. (1999). Acidic and Basic Reagents. Handbook of Reagents for Organic Synthesis. New York: John Wiley & Sons, Inc. ISBN 9780471979258.

From Wikipedia, the free encyclopedia

Iron(III) chloride

Iron(III) chloride (anhydrous) Iron(III) chloride (hydrate)
Names
IUPAC names Iron(III) chloride Iron trichloride
Other names Ferric chloride Molysite Flores martis
Identifiers
CAS Number	7705-08-0  10025-77-1 (hexahydrate)  54862-84-9 (dihydrate)  64333-00-2 (3.5hydrate)
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30808
ChemSpider	22792
ECHA InfoCard	100.028.846
EC Number	231-729-4
PubChem CID	24380
RTECS number	LJ9100000
UNII	U38V3ZVV3V  0I2XIN602U (hexahydrate)  Y048945596 (dihydrate)
UN number	1773 (anhydrous) 2582 (aqueous solution)
CompTox Dashboard (EPA)	DTXSID8020622
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 aqueous 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 (anhydrous or hexahydrate, 25 °C)[1]
Solubility in Acetone Methanol Ethanol Diethyl ether[1]	630 g/L (18 °C) Highly soluble 830 g/L Highly soluble
Magnetic susceptibility (χ)	+13,450·10−6 cm3/mol[2]
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 geometry	Octahedral
Hazards[5][6][Note 1]
GHS labelling:
Pictograms
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)	2 0 0
Flash point	Non-flammable
NIOSH (US health exposure limits):
REL (Recommended)	TWA 1 mg/m3[4]
Safety data sheet (SDS)	ICSC 1499
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
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

Iron(III) chloride describes the inorganic compounds with the formula FeCl₃(H₂O)_x. Also called ferric chloride, these compounds are available both in an anhydrous and hydrated forms. They are common source of iron in the +3 oxidation state. The hydrate and the anhydrous derivative have distinct properties.

Structure and properties[edit]

All forms of ferric chloride are paramagnetic, owing to the presence of five unpaired electrons residing in 3d orbitals. This electronic configuration places electrons in molecular orbitals that are antibonding with respect to ligands. Thus, iron(III) chlorides are labile, undergoing rapid ligand exchange in solution. In contrast to their kinetic lability, iron(III) chlorides are thermodynamically robust, as reflected by the vigorous methods applied to their synthesis.

Anhydrous[edit]

The anhydrous compound is a 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 BiI₃ structure, with octahedral Fe(III) centres 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 D_3h point group molecular symmetry) at higher temperature, in competition with its reversible decomposition to give iron(II) chloride and chlorine gas.^[8]

Hydrates[edit]

In addition to the anhydrous material, ferric chloride aggressively forms hydrates upon exposure to water, reflecting its Lewis acidity. Four of these hydrates have been crystallized and examined by X-ray crystallography. They all feature trans—[FeCl₂(H₂O)₄]⁺ cations, with either chloride or [FeCl₄]⁻ as the anions.^[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]

Solution[edit]

Aqueous solutions of ferric chloride are characteristically yellow, in contrast to the pale pink solutions of [Fe(H₂O)₆]³⁺. Thus, the chloride ligand significantly influences the optical properties of the iron center. According to spectroscopic measurements, the main species in aqueous solutions of ferric chloride are the octahedral [FeCl₂(H₂O)₄]⁺ (stereochemistry unspecified) and the tetrahedral [FeCl₄]⁻.^[9] The cationic aquo complex is strongly acidic:^[11][9]

[FeCl₂(H₂O)₄)]⁺ ⇌ [FeCl₂(OH)(H₂O)₃] + H⁺

Anhydrous iron(III) chloride dissolves in diethyl ether and tetrahydrofuran forming 1:2 adducts of the formula FeCl₃(ether)₂. In these complexes, the iron is pentacoordinate.^[12]

Preparation[edit]

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

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.^[13] A similar but laboratory scale process also has been described.^[14]

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

1. Dissolving iron ore in hydrochloric acid

   Fe₃O₄ + 8 HCl → FeCl₂ + 2 FeCl₃ + 4 H₂O

2. Oxidation of iron(II) chloride with chlorine

   2 FeCl₂ + Cl₂ → 2 FeCl₃

3. 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.^[15] Similarly, dehydration can be effected with trimethylsilyl chloride:^[16]

FeCl₃·6H₂O + 12 (CH₃)₃SiCl → FeCl₃ + 6 ((CH₃)₃Si)₂O + 12 HCl

Reactions[edit]

The reactivity of ferric chloride reveals two trends: It is a Lewis acid and an oxidizing agent.

Lewis-acid reactions[edit]

Reactions of iron(III) chlorides reflect the description of iron(III) as oxophilic and a hard Lewis acid. The rapidity of these reactions are consistent with the lability of ferric ion, reflecting its typical high-spin electronic configuration. Thus, oxalate salts react rapidly with aqueous iron(III) chloride to give [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 superceded by spectroscopic methods, the ferric chloride test is a traditional colorimetric test.^[17] The affinity of iron(III) for phenols is exploited in the Trinder spot test.

Myriad other manifestation of the oxophiliicty of iron(III) chloride are available. When heated with iron(III) oxide at 350 °C it reactions to give iron oxychloride:^[18]

FeCl₃ + Fe₂O₃ → 3FeOCl

Alkali metal alkoxides react to give the iron(III) alkoxide complexes. These products have more complicated structures that the anhydrous iron(III) chloride.^[19][20] In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl₃ and sodium ethoxide:

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., FeCl₃(OP(C₆H₅)₃)₂. The related 1:2 complex , has been crystallized from ether solution.^[12]

Iron(III) chloride also reacts with tetraethylammonium chloride to give the yellow salt of the tetrachloroferrate ion ((Et₄N)[FeCl₄]). Similarly combining FeCl₃ with NaCl and KCl gives Na[FeCl₄] and K[FeCl₄], respectively.^[21]

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.

Redox reactions[edit]

Iron(III) chloride is a mild oxidizing agent. It serves as one-electron oxidant illustrated by its reaction with copper(I) chloride to give copper(II) chloride and iron(II) chloride.

FeCl₃ + CuCl → FeCl₂ + CuCl₂

In a comproportionation reaction, iron(III) chloride reacts with iron powder to form iron(II) chloride:^[13]

2 FeCl₃ + Fe → 3 FeCl₂

A traditional synthesis of anhydrous ferrous chloride is the reduction of FeCl₃ with chlorobenzene:^[22]

2 FeCl₃ + C₆H₅Cl → 2 FeCl₂ + C₆H₄Cl₂ + HCl

Organometallic chemistry[edit]

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 etherial solvents, which are compatible with the nucleophilic alkylating agents. Such studies may be relevant to the mechanism of FeCl₃-catalyzed cross coupling reactions.^[23] 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.^[24] Illustrating the sensitivity of these reactions, methyl lithium LiCH₃ reacts with iron(III) chloride to give lithium tetrachloroferrate(II) Li₂[FeCl₄]:^[25]

2 FeCl₃ + LiCH₃ → FeCl₂ + Li[FeCl₄] + 0.5 CH₃CH₃

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.^[26] These diketonate complexes have the advantages that they do not form hydrates, unlike iron(III) chloride, and they are more soluble in relevant solvents.^[23]
Cyclopentadienyl magnesium bromide undergoes a complex reaction with iron(III) chloride, resulting in ferrocene:^[27]

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.^[28]

Uses[edit]

Water treatment[edit]

In the largest application iron(III) chloride is used in sewage treatment and drinking water production as a coagulant and flocculant.^[29] In this application, an aqueous solution of FeCl₃ is treated with base to form a floc of iron(III) hydroxide (Fe(OH)₃), also formulated as FeO(OH) (ferrihydrite). This floc facilitates the separation of suspended materials, clarifying the water.^[13]

Iron(III) chloride is also used to remove soluble phosphate from wastewater. Iron(III) phosphate is insoluble and thus precipitates as a solid.^[30] One potential advantage to its use in water treatment, ferric ion oxidizes (deodorizes) hydrogen sulfide.^[31]

Etching and metal cleaning[edit]

It is also used as a leaching agent in chloride hydrometallurgy,^[32] for example in the production of Si from FeSi (Silgrain process by Elkem).^[33]

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

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).^[34]

Iron(III) chloride is used in many other hobbies involving metallic objects.^{[35][36][37][38][39]}

Organic chemistry[edit]

In industry, iron(III) chloride is used as catalyst for the reaction of ethylene with chlorine, forming ethylene dichloride (1,2-dichloroethane):^[40]

H₂C=CH₂ + Cl₂ → ClCH₂CH₂Cl

Ethylene dichloride is a commodity chemical, which is mainly used for the industrial production of vinyl chloride, the monomer for making PVC.

Several reagents for organic synthesis have been developed based especially on anhydrous iron(III) chloride:

• Ferric chloride on silica gel is a reagent that has high reactivity towards several oxygen-containing functional groups. When the reagent is dry, its acidity and high affinity for water lead to dehydration and pinacol-type rearrangement reactions. When the reagent is moistened, it instead induces hydrolysis or epimerization reactions.^[41]
• Ferric chloride on alumina is used to accelerate ene reactions.^[42]
• Ferric chloride in conjunction with NaI in acetonitrile solution reduces organic azides to primary amines.^[43]
• When mixed with sodium hydride, iron(III) chloride gives a hydride reducing agent. This reagent has been shown to convert alkenes and ketones into alkanes and alcohols, respectfully.^[44]

As a reagent in organic chemistry, iron(III) chloride has attracted interest for both its redox activity and its Lewis acidity. Furthermore, because they are inexpensive and relatively nontoxic, iron chlorides have been widely examined.^[26] 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.^[45] Iron(III) chloride oxidizes naphthols to naphthoquinones:^[26][46]

Histology[edit]

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.

Safety[edit]

Anhydrous iron(III) chloride is harmful, highly corrosive, and acidic.^[26]

Natural occurrence[edit]

The natural counterpart of FeCl₃ is the rare mineral molysite, usually related to volcanic and other-type fumaroles.^[47][48]

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.^[49]

The clouds of Venus are hypothesized to contain approximately 1% FeCl₃ dissolved in sulfuric acid.^[50][51]

Notes[edit]

References[edit]

Further reading[edit]

1. Lide DR, ed. (1990). CRC Handbook of Chemistry and Physics (71st ed.). Ann Arbor, MI, USA: CRC Press. ISBN 9780849304712.
2. Stecher PG, Finkel MJ, Siegmund OH, eds. (1960). The Merck Index of Chemicals and Drugs (7th ed.). Rahway, NJ, USA: Merck & Co.
3. Nicholls D (1974). Complexes and First-Row Transition Elements, Macmillan Press, London, 1973. A Macmillan chemistry text. London: Macmillan Press. ISBN 9780333170885.
4. Wells AF (1984). Structural Inorganic Chemistry. Oxford science publications (5th ed.). Oxford, UK: Oxford University Press. ISBN 9780198553700.
5. Reich HJ, Rigby HJ, eds. (1999). Acidic and Basic Reagents. Handbook of Reagents for Organic Synthesis. New York: John Wiley & Sons, Inc. ISBN 9780471979258.

У этого термина существуют и другие значения, см. Хлорид железа.

Хлорид железа​(III)​
Общие
Систематическое наименование	Хлорид железа​(III)​
Хим. формула	FeCl3
Физические свойства
Состояние	твердый
Молярная масса	162.5 г/моль
Плотность	2,8 г/см³
Термические свойства
Температура
• плавления	306 °C
• кипения	315 °C
Химические свойства
Растворимость
• в воде	92 г/100 мл
Классификация
Рег. номер CAS	7705-08-0
Безопасность
ЛД50	440 мг/кг (крысы, орально)
Пиктограммы ECB
NFPA 704	0 3 0 COR
Приведены данные для стандартных условий (25 °C, 100 кПа), если не указано иное.

Хлорид железа(III) (хлорное железо, также — трихлорид железа) FeCl₃ — средняя соль трёхвалентного железа и соляной кислоты, слабое амфотерное соединение.

Физические свойства

Мерцающие, черно-коричневые, либо темно-красные, либо фиолетовые в проходящем свете, зеленые в отраженном свете листочки с металлическим блеском. Сильно гигроскопичен, на воздухе превращается в гидрат FeCl₃· 6Н₂О — гигроскопичные жёлтые, по другим источникам желто-коричневые кристаллы, хорошо растворимые в воде (при 20 °C в 100 г воды растворяется 91,9 г безводной соли).
T_пл 309 °C.

Методы получения

• Самым простым методом получения трихлорида железа является действие на железные опилки или раскалённую железную проволоку^[1] газообразным хлором. При этом, в отличие от действия соляной кислоты, образуется соль трёхвалентного железа — выделяется бурый дым из мельчайших её частиц^[2]. Также можно получить трихлорид железа взаимодействием железа с хлором на свету. Так как молекулы хлора распадаются в присутствии света на высокореакционноспособные атомы-радикалы:

[math]displaystyle{ mathsf{2Fe + 3Cl_2 xrightarrow{hnu, +250^oC} 2FeCl_3} }[/math]

• Также трихлорид получается при окислении хлором хлорида железа(II):

[math]displaystyle{ mathsf{2FeCl_2 + Cl_2 rightarrow 2FeCl_3} }[/math]

• Также существует метод окисления оксидом серы(IV):

[math]displaystyle{ mathsf{4FeCl_2 + SO_2 + 4HCl rightarrow 4FeCl_3 + S + 2H_2O} }[/math]

• Другим способом получения трихлорида железа (FeCl3) является взаимодействие оксида железа(III) с соляной кислотой, сопровождающееся выделением воды и энергии в виде тепла:

[math]displaystyle{ mathsf{Fe_2O_3 + 6HCl rightarrow 2FeCl_3 + 3H_2O} }[/math]

Химические свойства

• При нагревании в атмосферном давлении до температуры плавления начинается медленное разложение трихлорида железа с образованием дихлорида и молекулярного хлора:

[math]displaystyle{ mathsf{2FeCl_3 rightarrow 2FeCl_2 + Cl_2uparrow} }[/math]

• За счёт того, что трихлорид железа является сильной кислотой Льюиса, он вступает во взаимодействие с некоторыми другими хлоридами, при этом образуются комплексные соли тетрахлороферратной кислоты:

[math]displaystyle{ mathsf{FeCl_3 + Cl^- rightarrow [FeCl_4]^-} }[/math]

• При нагревании до 350 °C с оксидом железа(III) образуется оксохлорид железа:

[math]displaystyle{ mathsf{FeCl_3 + Fe_2O_3 rightarrow 3FeOCl} }[/math]

• Соли трёхвалентного железа являются слабыми окислителями, в частности, трихлорид железа хорошо окисляет металлическую медь, переводя её в растворимые хлориды:

[math]displaystyle{ mathsf{FeCl_3 + Cu rightarrow FeCl_2 + CuCl} }[/math]

[math]displaystyle{ mathsf{FeCl_3 + CuCl rightarrow FeCl_2 + CuCl_2} }[/math]

• реагирует с иодоводородом:

[math]displaystyle{ mathsf{2FeCl_3 + 2HI rightarrow 2FeCl_2 + I_2 + 2HCluparrow} }[/math]

Восстанавливается сернистым газом, сульфитами и органическими спиртами:

[math]displaystyle{ mathsf{2FeCl_3 + SO_2 +2H_2O longrightarrow 2FeCl_2 + H_2SO_4 + 2HCluparrow} }[/math]

[math]displaystyle{ mathsf{2FeCl_3 + Na_2SO_3 + H_2O longrightarrow 2FeCl_2 + Na_2SO_4 +2HCluparrow} }[/math]

[math]displaystyle{ mathsf{4FeCl_3 + C_2H_5OH + H_2O longrightarrow 4FeCl_2 + CH_3COOH + 4HCluparrow} }[/math]

[math]displaystyle{ mathsf{6FeCl_3 + CH_3OH + H_2O longrightarrow 6FeCl_2 + CO_2uparrow +6HCluparrow} }[/math]

Применение

• Хлорид железа(III) применяется при травлении печатных плат (радиотехника, системотехника).
• Используется для травления печатных форм (офорт, цинкография), как альтернатива азотной кислоте, реакция с которой сопровождается выделением высокотоксичных паров («лисий хвост»).
• Используется в кузнечном деле для проявления рисунка железа.
• Применяется как протрава при крашении тканей.
• В промышленных масштабах применяется как коагулянт для очистки воды.
• За счёт чётко выраженных кислотных свойств широко применяется в качестве катализатора в органическом синтезе. Например, для реакции электрофильного замещения в ароматических углеводородах.

Безопасность

Хлорид железа(III) является токсичным, высококоррозионным соединением. Безводная соль служит осушителем.

На вкус представляет терпкую безвкусную массу. Язык приобретает сильную сухость и становится губкой.

См. также

• Хлорид железа(II)

Примечания

Iron(III) chloride
Archivo:Iron(III) chloride hexahydrate.jpg
Archivo:Iron-trichloride-sheet-3D-polyhedra.png	Archivo:Iron-trichloride-sheets-stacking-3D-polyhedra.png
IUPAC name	Iron(III) chloride Iron trichloride
Other names	Ferric chloride Molysite Flores martis
Identifiers
CAS number	7705-08-0,  10025-77-1 (hexahydrate) 10025-77-1 (hexahydrate)
PubChem	24380
UN number	1773 (anhydrous) 2582 (aq. soln.)
RTECS number	LJ9100000
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
MSDS	ICSC 1499
EU Index	Not listed
Main hazards	Corrosive, especially in solution
NFPA 704	0 3 2
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
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Iron(III) chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl₃. 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 coagulant 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.

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.^[2]

Preparation[]

Anhydrous iron(III) chloride may be prepared by union of the elements:^[3]

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.

1. Dissolving pure iron in a solution of iron(III) chloride
   :Fe(s) + 2 FeCl₃(aq) → 3 FeCl₂(aq)
2. Dissolving iron ore in hydrochloric acid
   :Fe₃O₄(s) + 8 HCl(aq) → FeCl₂(aq) + 2 FeCl₃(aq) + 4 H₂O
3. Upgrading the 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.^[4] The hydrate cannot be converted to anhydrous iron(III) chloride by only heat, as instead HCl is evolved and iron oxychloride forms.

Reactions[]

Archivo:Iron(III) chloride.JPG

Iron(III) chloride under goes hydrolysis to give a an acidic solution. When heated with iron(III) oxide at 350 °C, iron(III) chloride gives iron oxychloride, a layered solid and intercalation host.^{[citation needed]}

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^[5]. The compounds can be dimeric or trimeric^[6]. In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl₃ and Sodium ethoxide:^[7][8]

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 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.^[9] 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,^[10] for example in the production of Si from FeSi. (Silgrain process)^[11]

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.^[12]

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:

Iron(III) chloride as a catalyst

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.^[13] 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 and acetylsalicylic acid (aspirin). Both these compounds contain phenolic OH groups.

Other uses[]

• Used in anhydrous form as a drying reagent in certain reactions.
• 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 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.^[14]
• 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.^[15]
• Used in an animal thrombosis model ^[16]

Safety[]

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

See also[]

• Iron(II) sulfate
• Aluminium chloride

References[]

Further reading[]

1. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
2. The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
3. D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.
4. A.F. Wells, ‘Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
5. J. March, Advanced Organic Chemistry, 4th ed., p. 723, Wiley, New York, 1992.
6. Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents, (H. J. Reich, J. H. Rigby, eds.), Wiley, New York, 1999.

Plantilla:Iron compounds
Plantilla:Good article

Iron(III) chloride
Archivo:Iron(III) chloride hexahydrate.jpg
Archivo:Iron-trichloride-sheet-3D-polyhedra.png	Archivo:Iron-trichloride-sheets-stacking-3D-polyhedra.png
IUPAC name	Iron(III) chloride Iron trichloride
Other names	Ferric chloride Molysite Flores martis
Identifiers
CAS number	7705-08-0,  10025-77-1 (hexahydrate) 10025-77-1 (hexahydrate)
PubChem	24380
UN number	1773 (anhydrous) 2582 (aq. soln.)
RTECS number	LJ9100000
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
MSDS	ICSC 1499
EU Index	Not listed
Main hazards	Corrosive, especially in solution
NFPA 704	0 3 2
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
(what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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	Commons: en Imágenes
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Iron(III) chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl₃. 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 coagulant 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.

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.^[2]

Preparation[]

Anhydrous iron(III) chloride may be prepared by union of the elements:^[3]

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.

1. Dissolving pure iron in a solution of iron(III) chloride
   :Fe(s) + 2 FeCl₃(aq) → 3 FeCl₂(aq)
2. Dissolving iron ore in hydrochloric acid
   :Fe₃O₄(s) + 8 HCl(aq) → FeCl₂(aq) + 2 FeCl₃(aq) + 4 H₂O
3. Upgrading the 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.^[4] The hydrate cannot be converted to anhydrous iron(III) chloride by only heat, as instead HCl is evolved and iron oxychloride forms.

Reactions[]

Archivo:Iron(III) chloride.JPG

Iron(III) chloride under goes hydrolysis to give a an acidic solution. When heated with iron(III) oxide at 350 °C, iron(III) chloride gives iron oxychloride, a layered solid and intercalation host.^{[citation needed]}

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^[5]. The compounds can be dimeric or trimeric^[6]. In the solid phase a variety of multinuclear complexes have been described for the nominal stoichiometric reaction between FeCl₃ and Sodium ethoxide:^[7][8]

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 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.^[9] 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,^[10] for example in the production of Si from FeSi. (Silgrain process)^[11]

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.^[12]

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:

Iron(III) chloride as a catalyst

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.^[13] 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 and acetylsalicylic acid (aspirin). Both these compounds contain phenolic OH groups.

Other uses[]

• Used in anhydrous form as a drying reagent in certain reactions.
• 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 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.^[14]
• 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.^[15]
• Used in an animal thrombosis model ^[16]

Safety[]

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

See also[]

• Iron(II) sulfate
• Aluminium chloride

References[]

Further reading[]

1. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
2. The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
3. D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.
4. A.F. Wells, ‘Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
5. J. March, Advanced Organic Chemistry, 4th ed., p. 723, Wiley, New York, 1992.
6. Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents, (H. J. Reich, J. H. Rigby, eds.), Wiley, New York, 1999.

Plantilla:Iron compounds
Plantilla:Good article

Соединения железа

Алюминат железа II (Fe(AlO2)2) Алюминат железа II Арсенат железа II (Fe3(AsO4)2) Железо мышьяковокислое Арсенат железа III (FeAsO4) Мышьяковокислое железо Ацетат железа II (Fe(CH3COO)2) Железо уксуснокислое Ацетат железа III (Fe(CH3COO)3) Уксуснокислое железо Берлинская лазурь () Прусская Синь Бромид железа II (FeBr2) Бромистое железо Бромид железа III (FeBr3) Трибромид железа Бромид железа II,III (Fe3Br8) Железо бромистое Ванадат железа III (FeVO4) Железо ванадиевокислое Вольфрамат железа II (FeWO4) Железо вольфрамовокислое Гексаплутонийжелезо (FePu6) Гексаплутонийжелезо Гексахлороплатинат IV железа (Fe[PtCl6]) Гексахлороплатеат железа Гексацианоферрат II железа II (Fe2[Fe(CN)6]) Гексацианоферрат железа II Гексацианоферрат II железа III (Fe4[Fe(CN)6]3) Гексацианоферрат железа III Гексацианоферрат III железа II,III (FeIII4FeII3[Fe(CN)6]6) Гексацианоферрат железа II,III Гексацианоферрат III железа II (Fe3[Fe(CN)6]2) Турнбулева синь Гексацианоферрат II калия (K4[Fe(CN)6]) Желтая кровяная соль Гексацианоферрат III калия (K3[Fe(CN)6]) Красная кровяная соль Гидроксид железа II (Fe(OH)2) Гидроксид железа II Гидроксид железа III (Fe(OH)3) Гидроксид железа III Динитрозилдикарбонилжелезо (Fe(CO)2(NO)2) Динитрозилдикарбонилжелезо Дипразеодимгептадекажелезо (Fe17Pr2) Гептадекажелезодипразеодим Диренийтрижелезо (Fe3Re2) Трижелезодирений Дисамарийгептадекажелезо (Fe17Sm2) Гептадекажелезодисамарий Диселенид железа (FeSe2) Железо селенистое Дисилицид железа (FeSi2) Железо кремнистое Дистаннид железа (FeSn2) Дистаннид железа Дистаннид трижелеза (Fe3Sn2) Дистаннид трижелеза Дисульфид железа II (FeS2) Дисульфид железа Дителлурид железа (FeTe2) Дителлурид железа Дихромат железа III (Fe2(Cr2O7)3) Хромовокислое железо Додекакарбонилтрижелезо (Fe3(CO)12) Додекакарбонилтрижелезо Железо (Fe) Железистосинеродистая кислота (H4[Fe(CN)6]) Кислота железистосинеродистая Железониобий (FeNb) Железониобий Железосинеродистая кислота (H3[Fe(CN)6]) Кислота железосинеродистая Йодид железа II,III (Fe3I8) Йодистое железо Йодид железа II (FeI2) Железо йодистое Карбонат железа II (FeCO3) Железо углекислое Лактат железа II (Fe(C3H5O3)2) Железо молочнокислое Лактат железа III (Fe(C3H5O3)3) Молочнокислое железо Метаванадат железа III (Fe(VO3)3) Ванадиевокислое железо Метагидроксид железа (FeO(OH)) Железо метагидроксид Молибдат железа II (FeMoO4) Железо молибденовокислое Нитрат железа II (Fe(NO3)2) Железо азотнокислое Нитрат железа III (Fe(NO3)3) Азотнокислое железо Нитрид дижелеза (Fe2N) Железо азотистое Оксалат железа II (FeC2O4) Железо щавелевокислое Оксид железа II (FeO) Оксид железа Оксид железа III (Fe2O3) Окись железа ( Железный сурик ) Оксид железа II,III (Fe3O4) Закись-окись железа Оксихлорид железа (FeOCl) Оксид-хлорид железа Пентакарбонилжелезо ([Fe(CO)5]) Пентакарбонил железа Перхлорат железа II (Fe(ClO4)2) Железо хлорнокислое Пирофосфат железа III (Fe4(P2O7)3) Железо пирофосфорнокислое Пирофосфат железа III-натрия (FeNaP2O7) Фосфорнокислое железо-натрий Платинажелезо (FePt) Железоплатина Плутонийдижелезо (Fe2Pu) Плутонийдижелезо Празеодимдижелезо (Fe2Pr) Дижелезопразеодим Ржавчина Самарийдижелезо (Fe2Sm) Дижелезосамарий Самарийпентажелезо (Fe5Sm) Пентажелезосамарий Самарийтрижелезо (Fe3Sm) Трижелезосамарий Селенид железа II (FeSe) Селенистое железо Силикат железа II (FeSiO3) Железо кремнекислое Силицид дижелеза (Fe2Si) Кремнистое железо Силицид железа (FeSi) Соль Мора (FeSO4·(NH4)2SO4·6H2O) Сульфат аммония-железа II Станнид железа (FeSn) Станнид трижелеза (Fe3Sn) Сульфат железа (FeSO4) Железо сернокислое (Железный купорос) Сульфат железа II-калия (K2Fe(SO4)2) Сернокислое железо-калий Сульфат железа III (Fe2(SO4)3) Железо сернокислое III Сульфат железа III-аммония (NH4Fe(SO4)2·12H2O) Сернокислое железо-аммоний Сульфат железа III-калия (KFe(SO4)2) Сернокислое железо-калий Сульфид железа II,III (Fe3S4) Сульфид железа II (FeS) Сульфид железа II-меди II (CuFeS2) Сульфид железа III (Fe2S3) Сульфид железа III-калия (KFeS2) Сернистое железо-калий Сульфит железа II (FeSO3) Железо сернистокислое Танталат железа II (Fe(TaO3)2) Железо танталовокислое Тартрат железа II (FeC4H4O6) Железо виннокислое Теллурид железа II (FeTe) Железо теллуристое Теллурид железа III (Fe2Te3) Теллуристое железо Тетракарбонилдигидриджелезо (H2Fe(CO)4) Тетракарбонилжелезо (Fe(CO)4) Тетракарбонил железа Тиосульфат железа II (FeSO3S) Тиосернокислое железо Тиоцианат железа II (Fe(SCN)2) Железо роданистое Тиоцианат железа III (Fe(SCN)3) Тиоциановокислое железо Титанат железа II (FeTiO3) Титановокислое железо Триренийдижелезо (Fe2Re3) Дижелезотрирений Формиат железа III (Fe(CHO2)3) Железо муравьинокислое Фосфат железа II (Fe3(PO4)2) Железо фосфорнокислое Фосфат железа III (FePO4) Фосфорнокислое железо Фосфинат железа III (Fe(PH2O2)3) Железо фосфорноватистокислое ( гипофосфит железа ) Фторид железа II (FeF2) Железо фтористое Фторид железа III (FeF3) Фтористое железо Хлорид железо II (FeCl2) Железо двухлористое Хлорид железа III (FeCl3) Железо треххлористое Хлорид железа II,III (Fe3Cl8) Хлористое железо II,III Хлорид железа III-калия (FeCl3•2KCl•H2O) Хлористое железо-калий Хромат железа III (Fe2(CrO4)3) Железо хромовокислое Хромит железа II (Fe(СrO2)2) тетраоксид железа-дихрома Цианид железа II (Fe(CN)2) Железо цианистое Цитрат железа II (FeC6H6O7) Железо лимоннокислое Цитрат железа III (FeC6H5O7) Лимоннокислое железо Цитрат железа III-аммония (Fe(NH4)3(C6H5O7)2) Лимоннокислое железо-аммоний

У этого термина существуют и другие значения, см. Хлорид железа.

Хлорид железа(III)
Общие
Систематическое наименование	Хлорид железа(III)
Химическая формула	FeCl3
Физические свойства
Состояние (ст. усл.)	твердый
Отн. молек. масса	162 а. е. м.
Молярная масса	162.2 г/моль
Плотность	2,8 г/см³
Термические свойства
Температура плавления	306 °C
Температура кипения	315 °C
Химические свойства
Растворимость в воде	92 г/100 мл
Классификация
Рег. номер CAS	7705-08-0

Хлорид железа(III), хлорное железо FeCl₃ — средняя соль трёхвалентного железа и соляной кислоты.

Физические свойства

Мерцающие, черно-коричневые, либо темно-красные, либо фиолетовые в проходящем свете, зеленые в отраженном свете листочки с металлическим блеском. Сильно гигроскопичен, на воздухе превращается в гидрат FeCl₃· 6Н₂О — гигроскопичные жёлтые, по другим источникам желто-коричневые кристаллы, хорошо растворимые в воде (при 20 °C в 100 г воды растворяется 91,9 г безводной соли). T_пл 309 °C.

Методы получения

• Самым простым методом получения трихлорида железа является действие на железные опилки газообразным хлором. При этом, в отличие от действия соляной кислоты, образуется соль трёхвалентного железа:

• Также трихлорид получается при окислении хлором хлорида железа(II):

• Также существует достаточно интересный метод окисления оксидом серы(IV):

Химические свойства

• При нагревании в атмосферном давлении до температуры плавления начинается медленное разложение трихлорида железа с образованием дихлорида и молекулярного хлора:

• За счёт того, что трихлорид железа является сильной кислотой Льюиса, он вступает во взаимодействие с некоторыми другими хлоридами, при этом образуются комплексные соли тетрахлорожелезной кислоты:

• При нагревании до 350 °C с оксидом железа(III) образуется оксохлорид железа:

• Соли трёхвалентного железа являются слабыми окислителями, в частности, трихлорид железа хорошо окисляет металлическую медь, переводя её в растворимые хлориды:

Применение

• Хлорид железа(III) применяется при травлении печатных плат (радиотехника, системотехника).
• Используется для травления печатных форм (офорт, цинкография), как альтернатива азотной кислоты, реакция с которой сопровождается выделением высокотоксичных паров («лисий хвост»).
• Применяется как протрава при крашении тканей.
• В промышленных масштабах применяется как коагулянт для очистки воды.
• За счёт чётко выраженных кислотных свойств, широко применяется в качестве катализатора в органическом синтезе. Например, для реакции электрофильного замещения в ароматических углеводородах.

Безопасность

Хлорид железа(III) является токсичным, высококоррозионным соединением. Безводная соль служит осушителем.

См. также

• Хлорид железа(II)