Nepedia
Back to Discover
Advanced Reader
⚛️

Zinc chloride

physical science Maturity 11-13 Next article →

Zinc chloride is an inorganic chemical compound with the formula ZnCl2·nH2O. The "n" in the formula represents the number of water molecules attached to the structure. This number can range from 0 to 4.5, creating what scientists call hydrates. In its pure, anhydrous form, it is a colorless or white crystalline solid. It is also highly soluble, meaning it dissolves very easily in water. This compound is a versatile tool in both laboratory science and large-scale industry.

CSD CIF TOCMON02
CSD CIF TOCMON02

To create zinc chloride, scientists usually react zinc or its various compounds with hydrogen chloride. This can involve using zinc metal, zinc carbonate, zinc oxide, or zinc sulfide. When making hydrates, the process relies on the controlled evaporation of aqueous solutions. The specific temperature used during evaporation determines which hydrate is produced. For instance, evaporating at room temperature creates the 1.33-hydrate. Using lower evaporation temperatures results in higher hydrates.

CSD CIF TOCMON02
CSD CIF TOCMON02

The structure of zinc chloride is quite complex. Anhydrous zinc chloride can exist in four different crystalline shapes, known as polymorphs. These are labeled as the alpha, beta, gamma, and delta forms. Each of these forms features zinc centers surrounded by four chloride ligands in a tetrahedral arrangement. The delta form is particularly unstable in the open air. It can rapidly change into another polymorph when exposed to the atmosphere. This change likely happens because ions from absorbed water help the structure rearrange itself.

CSD CIF TOCMON02
CSD CIF TOCMON02

History shows that zinc chloride has been used for many different purposes. In 1839, Sir William Burnett promoted its use as a disinfectant and a wood preservative. During the cholera epidemic of 1849, the Royal Navy even conducted trials using dilute zinc chloride as a disinfectant. In 1855, Stanislas Sorel investigated an amorphous cement made from zinc oxide and aqueous zinc chloride. This research eventually led to the study of magnesium oxychloride cement, which is named after him. While Burnett had commercial success, his disinfectant was later replaced by carbolic acid.

CSD CIF TOCMON02
CSD CIF TOCMON02

In the world of chemistry, zinc chloride acts as a powerful Lewis acid. A Lewis acid is a substance that can accept electron pairs from other molecules. This property allows it to form complexes with many different Lewis bases. For example, it can form adducts with weak bases like tetrahydrofuran. It also reacts with ammonia to produce various ammine complexes. In organic chemistry, it is used as a catalyst to drive important reactions. One famous example is the production of the dye fluorescein from phthalic anhydride and resorcinol.

Preparation of Fluorescein
Preparation of Fluorescein

Industrial applications of zinc chloride are vast and reach many different sectors. In the textile industry, it is used for various processing tasks. In metallurgy, it serves as a flux for soldering. As a flux, it dissolves metal oxides to expose clean metal surfaces for better bonding. It is also essential for producing benzaldehyde. In Western countries alone, about 20,000 tons of benzaldehyde are produced annually using zinc chloride as a catalyst. This process involves the chlorination of toluene to create benzal chloride.

Modern science has also used zinc chloride to unlock new ways of building molecules. It is a common precursor for making organozinc reagents. These reagents are vital for the Negishi coupling, a reaction involving aryl or vinyl halides. This specific method was so significant to the field of chemistry that Ei-ichi Negishi won the Nobel Prize in Chemistry in 2010.

ZnCl2 Negishi
ZnCl2 Negishi

Furthermore, zinc chloride can help facilitate the formation of carbon-carbon bonds. This capability was first reported in 1880 by Joseph Achille Le Bel and William H. Greene. These diverse uses show how a single white solid can impact everything from medicine to heavy industry.

604 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

🖼️ Images & Media (6)
File:CSD CIF TOCMON02.png
CSD CIF TOCMON02.png
File:ZnCl2 aromatics (cropped indole).gif
ZnCl2 aromatics (cropped indole).gif
File:Preparation_of_Fluorescein.svg
Preparation_of_Fluorescein.svg
File:ZnCl2 benzylation (cropped).gif
ZnCl2 benzylation (cropped).gif
File:ZnCl2 aldol (cropped).gif
ZnCl2 aldol (cropped).gif
File:ZnCl2 Negishi.gif
ZnCl2 Negishi.gif
More to explore

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.