From Kirk-Othmer
Zinc chloride melts at 275°C, boils at 720°C, and is stable in the vapor phase up to 900°C. It is very hygroscopic, extremely water-soluble, and soluble in organic liquids such as alcohols, esters, ketones, ethers, amides, and nitrides. Hydrates with 1, 1.5, 2.5, 3, and 4 molecules of water have been identified and great care must be exercised to avoid hydration of the anhydrous form. Aqueous solutions of zinc chloride are acidic ( for 6 M) and, when partially neutralized, can form slightly soluble basic chlorides, eg, ZnCl2·4Zn(OH)2 [11073-22-6] and Zn(OH)Cl [14031-59-5]. Many other basic chlorides have been reported (58).
Anhydrous zinc chloride can be made from the reaction of the metal with chlorine or hydrogen chloride. It is usually made commercially by the reaction of aqueous hydrochloric acid with scrap zinc materials or roasted ore, ie, crude zinc oxide. The solution is purified in various ways depending upon the impurities present. For example, iron and manganese precipitate after partial neutralization with zinc oxide or other alkali and oxidation with chlorine or sodium hypochlorite. Heavy metals are removed with zinc powder. The solution is concentrated by boiling, and hydrochloric acid is added to prevent the formation of basic chlorides. Zinc chloride is usually sold as a 47.4 wt % (sp gr 1.53) solution, but is also produced in solid form by further evaporation until, upon cooling, an almost anhydrous salt crystallizes. The solid is sometimes sold in fused form.
The fumes of zinc chloride are highly toxic and can damage mucous membranes and cause pale gray cyanation. It can also ulcerate the skin of workers using it as a soldering flux or those handling wood impregnated with it (59).
The largest use of zinc chloride in the United States is in wood preservation, fluxes, and batteries . Zinc chloride solution dissolves vegetable fiber and is widely used in mercerizing cotton (qv), swelling fibers, as a mordant in dyeing, parchmentizing paper, etc . It dissolves metal oxides and is used as a flux, especially in galvanizing . Zinc electroplating is often done with a chloride bath ( ELECTROPLATING). In medicine, it is used in antiseptics, deodorants, dental cements, and disinfectants (qv). Zinc chloride solutions preserve wood and textiles and are used in adhesives (qv) and embalming fluids ( TEXTILES). Other uses are in organic synthesis, eg, in the preparation of methyl chloride and diethylzinc, as a dehydrant, in rubber vulcanization, and in oil refining.
58 .J. W. Hoffman and I. Lander, Aust. J. Chem. 21, 1439 (1968).
59. N. L. Sax, Dangerous Properties of Industrial Materials, 5th ed., Van Nostrand Reinhold, New York, 1979, pp. 1100-1104.