Aluminium chloride

This salt is made of metal and gas.

It looks like clear crystals. Sometimes it looks yellow.

This salt loves water. If it touches water, it makes a loud hiss. It can even make a stinging mist.

It is very useful in big factories. It helps make more metal. It can also help make dyes for colors.

Some people use it for health. It can help stop too much sweating.

It is not found in nature as a rock. It is a special tool for science.

Aluminium chloride is a special salt. It usually looks like clear crystals. Sometimes the crystals look yellow. This happens if iron is mixed in.

This salt is very helpful in science. It is a Lewis acid. This means it can help other things change. It is used as a catalyst. A catalyst helps a chemical change happen faster.

Factories use it to make many things. It helps make aluminium metal. It also helps make dyes for colors. Some people use a version of it to stop too much sweating.

This salt loves water. It is hygroscopic. This means it pulls water from the air. If you add liquid water, it makes a loud hiss. It can also make a stinging mist. This happens because it lets out hydrochloric acid.

You will not find this salt as a natural rock. However, a rare mineral called chloraluminite exists. People make this salt in large amounts. They do this by mixing aluminium metal with chlorine gas.

Aluminium chloride is a very useful chemical compound. It is often called aluminium trichloride. Most of the time, it looks like clear crystals. Sometimes the crystals appear yellow if iron is mixed in.

This substance is a Lewis acid. A Lewis acid is a type of chemical that can help other things change. It acts as a catalyst in many different ways. A catalyst is something that helps a chemical reaction happen faster. This makes it very important for making many different products.

This compound works in several different ways depending on its state. In its solid form, it has a layered structure. When it melts into a liquid, it forms something called a dimer. A dimer is a structure made of two parts joined together. At very high temperatures, these parts split into single pieces called monomers.

The liquid version has a lower density than the solid version. This change happens because the shape of the molecules changes too. It can also hold onto water to form a hexahydrate. This means it has six water molecules attached to it.

Scientists have known about these salts for a long time. In the 1700s, people called it muriate of alumina. They also used names like marine alum or muriated clay. It was first studied as a real chemical in the 1830s.

Today, we understand its structure much better. We know how it reacts with other substances like benzene. This knowledge helps us use it in big factories around the world.

There are many important facts about how we use it. One major use is in the Friedel-Crafts reaction. This process helps make things like anthraquinone, which is used for dyes.

It is also used to make aluminium metal. In the United States in 1993, people made about 21,000 tons of it. This number does not even count the amount used to make aluminium. Another use is in medicine to help treat excessive sweating.

You can think of aluminium chloride as a busy helper. It helps move pieces of molecules around to build new things. It is also very hungry for water. This is called being hygroscopic. If you put it in moist air, it will hiss and fume. This happens because it reacts with the water to release hydrochloric acid. While you won't find it as a common rock, a rare mineral called chloraluminite does exist in nature.

Aluminium chloride is a versatile inorganic compound. It is also known by the name aluminium trichloride. This substance is highly important in the chemical industry. It is used extensively to produce aluminium metal. It also serves as a powerful catalyst for many organic reactions.

A catalyst is a substance that helps a chemical reaction happen. In many cases, the aluminium chloride is not consumed by the reaction itself. However, it can sometimes bond strongly to the products. This can create a large amount of corrosive waste during industrial processes.

The compound exists in different forms depending on its environment. The anhydrous form is the version without water. It is often used in industrial settings. It can also form a hexahydrate. This means it contains six molecules of water for every unit of aluminium chloride. Both forms usually appear as colourless crystals. Sometimes, they look yellow due to contamination from iron(III) chloride. The hexahydrate form is actually a rare mineral called chloraluminite.

Another more complex hydrated mineral is known as cadwaladerite.

The structure of anhydrous aluminium chloride changes based on temperature. In its solid state, it has a layered, sheet-like structure. The chloride ions are arranged in a cubic close-packed pattern. When the substance melts, it becomes a dimer. A dimer is a structure consisting of two joined units. These dimers have a specific shape called the D2h point group. The liquid phase has a density of 1.78 g/cm3. This is lower than the solid density of 2.48 g/cm3. At even higher temperatures, the dimers split into monomers. These are single units with a trigonal planar shape.

Aluminium chloride is classified as a strong Lewis acid. A Lewis acid is a substance that can accept electron pairs from other molecules. This ability makes it very effective at starting chemical changes. One of its most famous uses is in Friedel-Crafts reactions. These reactions include both alkylation and acylation of arenes. Alkylation is more common but is more technically demanding to perform.

These processes are used to create important chemicals. For example, benzene and phosgene can be turned into anthraquinone. Anthraquinone is a key material used in the dyestuffs industry.

Beyond Friedel-Crafts reactions, this compound has many other roles in organic synthesis. It can catalyze the ene reaction. An example is adding methyl vinyl ketone to carvone. It can also induce hydrocarbon couplings and rearrangements. Scientists use it in the Fischer–Hafner synthesis to create metal complexes. This involves reacting aluminium and aluminium chloride with an arene. It is also used to make dichlorophenylphosphine. This is done by reacting benzene with phosphorus trichloride.

Even in medicine, it has a specific use. Topical aluminium chloride hexahydrate treats hyperhidrosis, which is excessive sweating.

History shows that people have known about these salts for centuries. In the 18th century, they were called muriate of alumina. Other old names included marine alum or muriated clay. Scientists began to study the chemistry of these salts in the 1830s. The way we make them has also been studied deeply. Large-scale manufacturing uses an exothermic reaction. This means the reaction releases heat. It involves reacting aluminium metal with chlorine or hydrogen chloride. These reactions happen at temperatures between 500 and 700 degrees Celsius.

One notable characteristic is that aluminium chloride is highly hygroscopic. This means it has a very strong affinity for water. If you expose anhydrous aluminium chloride to moist air, it will fume. If it touches liquid water, it will hiss. This happens because the water displaces the ligands to form the hexahydrate. This process is quite energetic. You cannot get the anhydrous form back simply by heating the hexahydrate. Instead, the substance loses hydrogen chloride. This leaves behind aluminium hydroxide or alumina. This intense reaction with water is why the substance is considered strongly corrosive.