![]() | |
![]() | |
Names | |
---|---|
IUPAC name Zinc chloride | |
Other names Zinc(II) chloride Neutral zinc chloride (1:2) Butter of zinc Zinc bichloride (archaic) | |
Identifiers | |
| |
3D model (JSmol) | |
ChEBI | |
ChEMBL | |
ChemSpider | |
DrugBank | |
ECHA InfoCard | 100.028.720 |
EC Number |
|
PubChem CID | |
RTECS number |
|
UNII | |
UN number | 2331 |
CompTox Dashboard (EPA) | |
| |
| |
Properties | |
ZnCl2 | |
Molar mass | 136.315 g/mol |
Appearance | white crystalline solid hygroscopic and very deliquescent |
Odor | odorless |
Density | 2.907 g/cm3 |
Melting point | 290 °C (554 °F; 563 K) [1] |
Boiling point | 732 °C (1,350 °F; 1,005 K) [1] |
432.0 g/ 100 g (25 °C) | |
Solubility | soluble in ethanol, glycerol and acetone |
Solubility in ethanol | 430.0 g/100ml |
−65.0·10−6 cm3/mol | |
Structure | |
Tetrahedral, linear in the gas phase | |
Pharmacology | |
B05XA12 ( WHO ) | |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards | Moderately toxic, irritant [2] |
GHS labelling: | |
![]() ![]() ![]() | |
Danger | |
H302, H314, H410 | |
P273, P280, P301+P330+P331, P305+P351+P338, P308+P310 | |
NFPA 704 (fire diamond) | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 350 mg/kg (rat, oral) 350 mg/kg (mouse, oral) 200 mg/kg (guinea pig, oral) 1100 mg/kg (rat, oral) 1250 mg/kg (mouse, oral) [3] |
LC50 (median concentration) | 1260 mg/m3 (rat, 30 min) 1180 mg-min/m3 [3] |
NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 1 mg/m3 (fume) [4] |
REL (Recommended) | TWA 1 mg/m3 ST 2 mg/m3 (fume) [4] |
IDLH (Immediate danger) | 50 mg/m3 (fume) [4] |
Safety data sheet (SDS) | External MSDS |
Related compounds | |
Other anions | Zinc fluoride Zinc bromide Zinc iodide |
Other cations | Cadmium chloride Mercury(II) chloride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Zinc chloride is the name of inorganic chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. [5] This salt is hygroscopic and even deliquescent. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn5(OH)8Cl2·H2O.
Four crystalline forms (polymorphs) of ZnCl2 are known: α, β, γ, and δ. Each case features tetrahedral Zn2+ centers. [6]
Form | Symmetry | Pearson symbol | Group | No | a (nm) | b (nm) | c (nm) | Z | ρ (g/cm3) |
---|---|---|---|---|---|---|---|---|---|
α | tetragonal | tI12 | I42d | 122 | 0.5398 | 0.5398 | 0.64223 | 4 | 3.00 |
β | tetragonal | tP6 | P42/nmc | 137 | 0.3696 | 0.3696 | 1.071 | 2 | 3.09 |
γ | monoclinic | mP36 | P21/c | 14 | 0.654 | 1.131 | 1.23328 | 12 | 2.98 |
δ | orthorhombic | oP12 | Pna21 | 33 | 0.6125 | 0.6443 | 0.7693 | 4 | 2.98 |
Here a, b, and c are lattice constants, Z is the number of structure units per unit cell, and ρ is the density calculated from the structure parameters. [7] [8] [9]
The orthorhombic form (δ) rapidly changes to one of the other forms on exposure to the atmosphere. A possible explanation is that the OH− ions originating from the absorbed water facilitate the rearrangement. [6] Rapid cooling of molten ZnCl2 gives a glass. [10]
Molten ZnCl2 has a high viscosity at its melting point and a comparatively low electrical conductivity, which increases markedly with temperature. [11] [12] As indicated by a Raman scattering study, the viscosity is explained by the presence of polymers, [13] . Neutron scattering study indicated the presence of tetrahedral {ZnCl4} centers, which requires aggregation of ZnCl2 monomers as well.. [14]
In the gas phase, ZnCl2 molecules are linear with a bond length of 205 pm.
Five hydrates of zinc chloride are known: ZnCl2(H2O)n with n = 1, 1.5, 2.5, 3 and 4. [15] The tetrahydrate ZnCl2(H2O)4 crystallizes from aqueous solutions of zinc chloride. [15]
Anhydrous ZnCl2 can be prepared from zinc and hydrogen chloride:
Hydrated forms and aqueous solutions may be readily prepared similarly by treating Zn metal, zinc carbonate, zinc oxide, and zinc sulfide with hydrochloric acid:
Unlike many other elements, zinc essentially exists in only one oxidation state, 2+, which simplifies the purification of the chloride.
Commercial samples of zinc chloride typically contain water and products from hydrolysis as impurities. Such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas. [16] Finally, the simplest method relies on treating the zinc chloride with thionyl chloride. [17]
Molten anhydrous ZnCl2 at 500–700 °C dissolves zinc metal, and, on rapid cooling of the melt, a yellow diamagnetic glass is formed, which Raman studies indicate contains the Zn2+
2 ion. [15]
A number of salts containing the tetrachlorozincate anion, ZnCl2−
4, are known. [11] "Caulton's reagent", V2Cl3(thf)6Zn2Cl6 is an example of a salt containing Zn2Cl2−
6. [18] [19] The compound Cs3ZnCl5 contains tetrahedral ZnCl2−
4 and Cl− anions. [6] No compounds containing the ZnCl4−
6 ion have been characterized. [6]
Zinc chloride dissolves readily in water to give ZnClxH2O(4−x) species and some free chloride. [20] [21] [22] Aqueous solutions of ZnCl2 are acidic: a 6 M aqueous solution has a pH of 1. [15] The acidity of aqueous ZnCl2 solutions relative to solutions of other Zn2+ salts (say the sulfate) is due to the formation of the tetrahedral chloro aqua complexes where the reduction in coordination number from 6 to 4 further reduces the strength of the O–H bonds in the solvated water molecules. [23]
In alkali solution, zinc chloride converts to various zinc hydroxychlorides. These include Zn(OH)3Cl2−, Zn(OH)2Cl2−
2, ZnOHCl2−
3, and the insoluble Zn5(OH)8Cl2·H2O. The latter is the mineral simonkolleite. [24] When zinc chloride hydrates are heated, HCl gas evolves and hydroxychlorides result. [25]
When solutions of zinc chloride are treated with ammonia, various complexes of "ammines" are produced. These include Zn(NH3)4Cl2·H2O and on concentration ZnCl2(NH3)2. [26] The former contains the Zn(NH3)62+ ion, [6] and the latter is molecular with a distorted tetrahedral geometry. [27] The species in aqueous solution have been investigated and show that Zn(NH3)42+ is the main species present with Zn(NH3)3Cl+ also present at lower NH3:Zn ratio. [28]
Aqueous zinc chloride reacts with zinc oxide to form an amorphous cement that was first investigated in 1855 by Stanislas Sorel. Sorel later went on to investigate the related magnesium oxychloride cement, which bears his name. [29]
When hydrated zinc chloride is heated, one obtains a residue of Zn(OH)Cl e.g. [30]
The compound ZnCl2·1⁄2HCl·H2O may be prepared by careful precipitation from a solution of ZnCl2 acidified with HCl. It contains a polymeric anion (Zn2Cl5−)n with balancing monohydrated hydronium ions, H5O2+ ions. [6] [31]
Cellulose dissolves in aqueous solutions of ZnCl2, and zinc-cellulose complexes have been detected. [32] Cellulose also dissolves in molten ZnCl2 hydrate and carboxylation and acetylation performed on the cellulose polymer. [33]
Thus, although many zinc salts have different formulas and different crystal structures, these salts behave very similarly in aqueous solution. For example, solutions prepared from any of the polymorphs of ZnCl2, 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:
Zinc chloride is used as a catalyst or reagent in diverse reactions conducted on an industrial scale. The partial hydrolysis of benzal chloride in the presence of zinc chloride is the main route to benzoyl chloride. It serves as a catalyst for the production of methylene-bis(dithiocarbamate). [5]
The combination of hydrochloric acid and ZnCl2, known as the "Lucas reagent", is effective for the preparation of alkyl chlorides from alcohols. Similar reactions are the basis of industrial routes from methanol and ethanol respectively to methyl chloride and ethyl chloride.
Zinc chloride is a common reagent in the laboratory useful Lewis acid in organic chemistry. [34]
Molten zinc chloride catalyses the conversion of methanol to hexamethylbenzene: [35]
Other examples include catalyzing (A) the Fischer indole synthesis, [36] and also (B) Friedel-Crafts acylation reactions involving activated aromatic rings [37] [38]
Related to the latter is the classical preparation of the dye fluorescein from phthalic anhydride and resorcinol, which involves a Friedel-Crafts acylation. [39] This transformation has in fact been accomplished using even the hydrated ZnCl2 sample shown in the picture above.
Zinc chloride also activates benzylic and allylic halides towards substitution by weak nucleophiles such as alkenes: [40]
In similar fashion, ZnCl2 promotes selective NaBH3CN 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 catalyzed Negishi coupling with aryl halides or vinyl halides. [41] In such cases the organozinc compound is usually prepared by transmetallation from an organolithium or a Grignard reagent, for example:
Zinc enolates, prepared from alkali metal enolates and ZnCl2, 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 ZnCl2 in DME/ether was used. [42] The chelate is more stable when the bulky phenyl group is pseudo-equatorial rather than pseudo-axial, i.e., threo rather than erythro.
The use of zinc chloride as a flux, sometimes in a mixture with ammonium chloride (see also Zinc ammonium chloride), involves the production of HCl and its subsequent reaction with surface oxides.
Zinc chloride reacts with metal oxides (MO) to give derivatives of the idealized formula MZnOCl2. [43] [ additional citation(s) needed ] This reaction is relevant to the utility of ZnCl2 solution as a flux for soldering — it dissolves passivating oxides, exposing the clean metal surface. [43] Fluxes with ZnCl2 as an active ingredient are sometimes called "tinner's fluid".
Zinc chloride forms two salts with ammonium chloride: (NH4)2ZnCl4 and (NH4)3ClZnCl4, which decompose on heating liberating HCl, just as zinc chloride hydrate does. The action of zinc chloride/ammonium chloride fluxes, for example, in the hot-dip galvanizing process produces H2 gas and ammonia fumes. [44]
Concentrated aqueous solutions of zinc chloride (more than 64% weight/weight zinc chloride in water) have dissolving starch, silk, and cellulose.
Relevant to its affinity for these materials, ZnCl2 is used as a fireproofing agent and in fabric "refresheners" such as Febreze. Vulcanized fibre is made by soaking paper in concentrated zinc chloride.
The zinc chloride smoke mixture ("HC") used in smoke grenades contains zinc oxide, hexachloroethane and granular aluminium powder, which, when ignited, react to form zinc chloride, carbon and aluminium oxide smoke, an effective smoke screen. [45]
Ninhydrin reacts with amino acids and amines to form a colored compound "Ruhemann's purple" (RP). Spraying with a zinc chloride solution forms a 1:1 complex RP:ZnCl(H2O)2, which is more readily detected as it fluoresces more intensely than RP. [46]
Dilute aqueous zinc chloride was used as a disinfectant under the name "Burnett's Disinfecting Fluid". [47] From 1839 Sir William Burnett promoted its use as a disinfectant as well as a wood preservative. [48] The Royal Navy conducted trials into its use as a disinfectant in the late 1840s, including during the cholera epidemic of 1849; and at the same time experiments were conducted into its preservative properties as applicable to the shipbuilding and railway industries. Burnett had some commercial success with his eponymous fluid. Following his death however, its use was largely superseded by that of carbolic acid and other proprietary products.
Zinc chloride is a chemical irritant of the eyes, skin, and respiratory system. [5] [49]
Hydroxylamine is an inorganic compound with the formula NH2OH. The material is a white crystalline, hygroscopic compound. Hydroxylamine is almost always provided and used as an aqueous solution. It is consumed almost exclusively to produce Nylon-6. It is also an intermediate in biological nitrification. The oxidation of NH3 to hydroxylamine is a step in biological nitrification.
Iron(III) chloride is the inorganic compound with the 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 colour depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red.
Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mineral cotunnite.
Neodymium(III) chloride or neodymium trichloride is a chemical compound of neodymium and chlorine with the formula NdCl3. This anhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl3·6H2O. Neodymium(III) chloride is produced from minerals monazite and bastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-based lasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination, corrosion protection of aluminium and its alloys, and fluorescent labeling of organic molecules (DNA).
Samarium(III) chloride, also known as samarium trichloride, is an inorganic compound of samarium and chloride. It is a pale yellow salt that rapidly absorbs water to form a hexahydrate, SmCl3.6H2O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.
Europium(III) chloride is an inorganic compound with the formula EuCl3. The anhydrous compound is a yellow solid. Being hygroscopic it rapidly absorbs water to form a white crystalline hexahydrate, EuCl3·6H2O, which is colourless. The compound is used in research.
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both are colourless crystals, but samples are often contaminated with iron(III) chloride, giving a yellow color.
Dysprosium(III) chloride (DyCl3), also known as dysprosium trichloride, is a compound of dysprosium and chlorine. It is a white to yellow solid which rapidly absorbs water on exposure to moist air to form a hexahydrate, DyCl3·6H2O. Simple rapid heating of the hydrate causes partial hydrolysis to an oxychloride, DyOCl.
Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoCl
2. The compound forms several hydrates CoCl
2·nH
2O, for n = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed. The anhydrous form is a blue crystalline solid; the dihydrate is purple and the hexahydrate is pink. Commercial samples are usually the hexahydrate, which is one of the most commonly used cobalt compounds in the lab.
Copper(I) chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid. Impure samples appear green due to the presence of copper(II) chloride (CuCl2).
Copper(II) chloride is the chemical compound with the chemical formula CuCl2. The anhydrous form is yellowish brown but slowly absorbs moisture to form a blue-green dihydrate.
Chromium(III) chloride (also called chromic chloride) describes any of several chemical compounds with the formula CrCl3 · xH2O, where x can be 0, 5, and 6. The anhydrous compound with the formula CrCl3 is a violet solid. The most common form of the trichloride is the dark green hexahydrate, CrCl3 · 6 H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.
Nickel(II) chloride (or just nickel chloride) is the chemical compound NiCl2. The anhydrous salt is yellow, but the more familiar hydrate NiCl2·6H2O is green. Nickel(II) chloride, in various forms, is the most important source of nickel for chemical synthesis. The nickel chlorides are deliquescent, absorbing moisture from the air to form a solution. Nickel salts have been shown to be carcinogenic to the lungs and nasal passages in cases of long-term inhalation exposure.
In polyatomic cations with the chemical formula PR+
4. These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions.
Rhodium(III) chloride refers to inorganic compounds with the formula RhCl3(H2O)n, where n varies from 0 to 3. These are diamagnetic solids featuring octahedral Rh(III) centres. Depending on the value of n, the material is either a dense brown solid or a soluble reddish salt. The soluble trihydrated (n = 3) salt is widely used to prepare compounds used in homogeneous catalysis, notably for the industrial production of acetic acid and hydroformylation.
In coordination chemistry, metal ammine complexes are metal complexes containing at least one ammonia ligand. "Ammine" is spelled this way due to historical reasons; in contrast, alkyl or aryl bearing ligands are spelt with a single "m". Almost all metal ions bind ammonia as a ligand, but the most prevalent examples of ammine complexes are for Cr(III), Co(III), Ni(II), Cu(II) as well as several platinum group metals.
Chromium(II) chloride describes inorganic compounds with the formula CrCl2(H2O)n. The anhydrous solid is white when pure, however commercial samples are often grey or green; it is hygroscopic and readily dissolves in water to give bright blue air-sensitive solutions of the tetrahydrate Cr(H2O)4Cl2. Chromium(II) chloride has no commercial uses but is used on a laboratory-scale for the synthesis of other chromium complexes.
Hexafluorosilicic acid is an inorganic compound with the chemical formula H
2SiF
6. Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless.
Zinc cyanide is the inorganic compound with the formula Zn(CN)2. It is a white solid that is used mainly for electroplating zinc but also has more specialized applications for the synthesis of organic compounds.
Chloroauric acid is an inorganic compound with the chemical formula H[AuCl4]. It forms hydrates H[AuCl4]·nH2O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4]− anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.