Zinc chloride 752048 222855807 2008-07-01T13:11:26Z AdultSwim 885146 <ref></ref> {{Chembox new | Name = Zinc chloride | ImageFile = Zinc chloride.jpg | ImageSize = 200px | ImageName = Zinc chloride hydrate | IUPACName = Zinc chloride | OtherNames = Zinc(II) chloride,<br />zinc dichloride,<br />butter of zinc, <br />Zinc butter | Section1 = {{Chembox Identifiers | CASNo = 7646-85-7 | RTECS = ZH1400000 }} | Section2 = {{Chembox Properties | Formula = ZnCl<sub>2</sub> | MolarMass = 136.315 g/mol | Appearance = White crystalline solid. | Density = 2.907 g/cm³, solid | Solubility = 432 g/100 mL (25 °C) | MeltingPt = 275 °C (548 K) | BoilingPt = 756 °C (1029 K) }} | Section3 = {{Chembox Structure | Coordination =<span style="font-size: 0.9em;">[[Tetrahedral]], 4-coordinate,<br />linear in the gas phase.</span> | CrystalStruct =<span style="font-size: 0.9em;">Four forms known<br />[[Close-packing|Hexagonal close-packed]] (δ)<br />is the only stable form<br />when anhydrous.</span> }} | Section7 = {{Chembox Hazards | ExternalMSDS = [http://physchem.ox.ac.uk/MSDS/ZI/zinc_chloride.html External MSDS] | EUClass = Irritant ('''I'''),<br />Corrosive('''C'''). | RPhrases = {{R34}}, {{R50}}, {{R53}} | SPhrases = {{S7/8}}, {{S28}}, {{S45}}, {{S60}},<br />{{S61}} }} | Section8 = {{Chembox Other | OtherAnions = [[Zinc fluoride]],<br />[[zinc bromide]],<br />[[zinc iodide]] | OtherCations = [[Copper(II) chloride]],<br />[[cadmium chloride]]}} }} '''Zinc chloride''' is the name of [[chemical compound]] with the [[chemical formula|formula]] [[zinc|Zn]][[chlorine|Cl]]<sub>2</sub> and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white and highly soluble in water. ZnCl<sub>2</sub> itself is [[hygroscopic]] and even [[deliquescent]]. Samples should therefore be protected from sources of moisture, including the water vapor present in ambient air. Zinc chloride finds wide application in [[textile]] processing, [[Flux (metallurgy)|metallurgical fluxes]], and chemical synthesis. ==Structure and basic properties== Four crystalline forms, so-called [[Polymorphism (materials science)|polymorph]]s, of ZnCl are known, and in each case the Zn<sup>2+</sup> ions are tetrahedrally coordinated to four chloride ligands.<ref name=Wells>Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref> Rapid cooling of molten ZnCl<sub>2</sub> gives a glass, that is, a rigid amorphous solid. Additionally ZnCl<sub>2</sub> forms [[water of crystallization|hydrate]]s and at least one mixed hydroxide, ZnClOH.<ref name=Wells/> The [[covalent]] character of the anhydrous material is indicated by its relatively low [[melting point]] of 275 °C. Further evidence for covalency is provided by the high solubility of the dichloride in [[ether]]ial solvents such as wherein it forms [[adduct]]s with the formula ZnCl, where L = [[ligand]] such as [[diethylether|O(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>]]. Consistent with the [[Lewis acid]]ity of Zn<sup>2+</sup>, aqueous solutions of ZnCl<sub>2</sub> are acidic solutions: a 6 [[Concentration#Molarity|M]] aqueous solution has a [[pH]] of 1.<ref name=Holleman>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> Four hydrates of zinc chloride are known. ZnCl<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub> crystallizes from aqueous solutions of zinc chloride. Also characterized are ZnCl<sub>2</sub>(H<sub>2</sub>O)<sub>n</sub> where n = 1, 1.5, 2.5, and 3.<ref name=Holleman/> When hydrated zinc chloride is heated, one obtains a residue of ZnOHCl. In aqueous solution, zinc chloride fully dissociates into Zn<sup>2+</sup>. Thus, although many zinc salts have different formulas and different [[crystal structure]]s, these salts behave very similarly in aqueous solution. For example, solutions prepared from any of the polymorphs of ZnCl<sub>2</sub> as well as other halides (bromide, iodide) and the sulfate can often be used interchangeably for the preparation of other zinc compounds. Illustrative is the preparation of zinc carbonate: :ZnCl<sub>2</sub>([[aqueous|aq]]) + [[Sodium carbonate|Na<sub>2</sub>CO<sub>3</sub>]](aq) → [[Zinc carbonate|ZnCO<sub>3</sub>]](s) + 2 [[Sodium chloride|NaCl]](aq) ==Preparation and purification== Anhydrous ZnCl<sub>2</sub> can be prepared from [[zinc]] and [[hydrogen chloride]]. :Zn + 2 HCl → ZnCl<sub>2</sub> + H<sub>2</sub> Hydrated forms and aqueous solutions may be readily prepared by treating pieces of Zn metal with concentrated hydrochloric acid. Zinc oxide and [[zinc sulfide]] react with HCl: :ZnS([[solid|s]]) + 2 [[Hydrochloric acid|HCl]](aq) → ZnCl<sub>2</sub>(aq) + [[Hydrogen sulfide|H<sub>2</sub>S]]([[gas|g]]) Unlike many other elements, zinc essentially exists in only one oxidation state, 2+, which simplifies purification. Commercial samples of zinc chloride typically contain [[water]] and products from [[hydrolysis]] product. Such samples may be purified by extraction into hot [[dioxane]], which is filtered hot and the filtrate is cooled to afford a precipitate of ZnCl<sub>2</sub>. Anhydrous samples can be purified by [[sublimation (chemistry)|sublimation]] in a stream of [[hydrogen chloride]] gas, followed by heating to 400 °C in a stream of dry [[nitrogen]] gas. Finally, the simplest method relies on treating the zinc chloride with [[thionyl chloride]].<ref>Pray, A. P. “Anhydrous Metal Chlorides” "Inorganic Syntheses," vol. XXVIII, 321-2, 1990ISBN 0-471-52619-3. Describes the formation of anhydrous LiCl, CuCl<sub>2</sub>, ZnCl<sub>2</sub>, CdCl<sub>2</sub>, ThCl<sub>4</sub>, CrCl<sub>3</sub>, FeCl<sub>3</sub>, CoCl<sub>2</sub>, and NiCl<sub>2</sub> from the corresponding hydrates.</ref> ==Applications== ====As a metallurgical flux==== Zinc chloride has the ability to attack metal oxides (MO) to give derivatives of the formula MZnOCl<sub>2</sub>. This reaction is relevant to the utility of ZnCl<sub>2</sub> as a [[Flux (metallurgy)|flux]] for [[soldering]] - it dissolves oxide coatings exposing the clean metal surface.<ref name=Holleman/> Fluxes with ZnCl as an active ingredient are sometimes called "Tinner's Fluid." Typically this flux was prepared by dissolving zinc foil in dilute [[hydrochloric acid]] until the liquid ceased to evolve hydrogen; for this reason, such flux was once known as [[killed spirits]]. Because of its corrosive nature, this flux is not suitable for situations where any residue cannot be cleaned away, such as electronic work. This property also leads to its use in the manufacture of [[magnesium oxide|magnesia]] cements for [[dental fillings]] and certain [[mouthwashes]] as an active ingredient. ====In organic synthesis==== In the laboratory, zinc chloride finds wide use, principally as a moderate-strength [[Lewis acid]]. It can [[catalysis|catalyse]] (A) the [[Fischer indole synthesis]]<ref>R. L. Shriner, W. C. Ashley, E. Welch, in ''Organic Syntheses Collective Volume 3'', p 725, Wiley, New York, 1955.</ref>, and also (B) [[Friedel-Crafts acylation]] reactions involving activated [[aromatic rings]]<ref>S. R. Cooper, in ''Organic Syntheses Collective Volume 3'', p 761, Wiley, New York, 1955.</ref><ref>S. Y. Dike, J. R. Merchant, N. Y. Sapre, ''Tetrahedron'', '''47''', 4775 (1991)</ref> [[Image:ZnCl2 aromatics.gif|480px]] Related to the latter is the classical preparation of the dye [[fluorescein]] from [[phthalic anhydride]] and [[resorcinol]], which involves a [[Friedel-Crafts acylation]].<ref>B. S. Furnell et al., ''Vogel's Textbook of Practical Organic Chemistry'', 5th edition, Longman/Wiley, New York, 1989.</ref> This transformation has in fact been accomplished using even the hydrated ZnCl<sub>2</sub> sample shown in the picture above. [[Image:ZnCl2 fluorescein.png|480px]] [[Hydrochloric acid]] alone reacts poorly with [[primary alcohol]]s and [[secondary alcohol]]s, but a combination of HCl with ZnCl<sub>2</sub> (known together as the "[[Lucas reagent]]") is effective for the preparation of alkyl chlorides. Typical reactions are conducted at 130 °C. This reaction probably proceeds via an [[SN2 reaction|S<sub>N</sub>2 mechanism]] with primary alcohols but [[SN1 reaction|S<sub>N</sub>1]] pathway with secondary alcohols. [[Image:ZnCl2 Lucas.gif|300px]] Zinc chloride also activates [[benzylic]] and [[allylic]] halides towards substitution by weak [[nucleophile]]s such as [[alkene]]s<ref>E. Bauml, K. Tschemschlok, R. Pock, H. Mayr, ''Tetrahedron Letters'', '''29''', 6925 (1988)</ref>: [[Image:ZnCl2 benzylation.gif|480px]] In similar fashion, ZnCl<sub>2</sub> promotes selective [[sodium cyanoborohydride|NaBH<sub>3</sub>CN]] reduction of tertiary, allylic or benzylic halides to the corresponding hydrocarbons. Zinc chloride is also a useful starting reagent for the synthesis of many [[organozinc]] reagents, such as those used in the palladium catalysed [[Negishi coupling]] with [[aryl halide]]s or [[vinyl halide]]s.<ref>S. Kim, Y. J. Kim, K. H. Ahn, ''Tetrahedron Letters'', '''24''', 3369 (1983).</ref> In such cases the organozinc compound is usually prepared by [[transmetallation]] from an [[organolithium]] or a [[Grignard reagent]], for example: [[Image:ZnCl2 Negishi.gif|480px]] Zinc [[enolate]]s, prepared from alkali metal enolates and ZnCl<sub>2</sub>, provide control of [[stereochemistry]] in [[aldol condensation]] reactions due to [[chelation]] on to the zinc. In the example shown below, the ''[[threo]]'' product was favored over the ''[[erythro]]'' by a factor of 5:1 when ZnCl<sub>2</sub> in [[Dimethoxyethane|DME]]/[[Diethyl ether|ether]] was used.<ref>H. O. House, D. S. Crumrine, A. Y. Teranishi, H. D. Olmstead, ''Journal of the American Chemical Society'', '''95''', 3310 (1973)</ref> The chelate is more stable when the bulky phenyl group is pseudo-[[equatorial]] rather than pseudo-[[axial]], i.e., ''threo'' rather than ''erythro''. [[Image:ZnCl2 aldol.gif|600px]] ====In textile processing==== Concentrated aqueous solutions of zinc chloride (more than 64% weight/weight zinc chloride in water) have the interesting property of dissolving [[starch]], [[silk]], and [[cellulose]]. Thus, such solutions cannot be filtered through standard filter papers. Relevant to its affinity for these materials, ZnCl<sub>2</sub> is used as a fireproofing agent and in fabric "refresheners" such as Febreze ==Safety considerations== Zinc salts are relatively non-toxic. Precautions that apply to anhydrous ZnCl<sub>2</sub> are those applicable to other anhydrous metal halides, i.e. hydrolysis can be exothermic and contact should be avoided. Concentrated solutions are acidic and [[corrosive]] and specifically attack cellulose and silk as [[Lewis acid]]s. See MSDS in table. ==References== <references/> ==Bibliography== # N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. # ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990. # ''The Merck Index'', 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960. # D. Nicholls, ''Complexes and First-Row Transition Elements'', Macmillan Press, London, 1973. # A. F. Wells, '''Structural Inorganic Chemistry'', 5th ed., Oxford University Press, Oxford, UK, 1984. # J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992. # G. J. McGarvey, in ''Handbook of Reagents for Organic Synthesis, Volume 1: Reagents, Auxiliaries and Catalysts for C-C Bond Formation'', (R. M. Coates, S. E. Denmark, eds.), pp. 220-3, Wiley, New York, 1999. ==External links== * [http://muby.itgo.com/zincchloride.html Grades and Applications of Zinc Chloride] *[http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5727 PubChem ZnCl<sub>2</sub> summary]. * [http://physchem.ox.ac.uk/MSDS/ZI/zinc_chloride.html External MSDS Data Sheet]. [[Category:Chlorides]] [[Category:Zinc compounds]] [[Category:Inorganic compounds]] [[Category:Metal halides]] [[Category:Deliquescent substances]] [[bg:Цинков хлорид]] [[da:ZnCl2]] [[de:Zinkchlorid]] [[es:Cloruro de zinc]] [[fr:Chlorure de zinc]] [[it:Cloruro di zinco]] [[nl:Zinkchloride]] [[ja:塩化亜鉛]] [[pl:Chlorek cynku]] [[pt:Cloreto de zinco]] [[sl:Cinkov klorid]] [[fi:Sinkkikloridi]] [[zh:氯化锌]]