Cyclohexane

This liquid is clear and has no color.

It smells like soap or cleaning tools. This liquid is very useful. It helps make nylon. Nylon is used for many things.

The tiny parts of it form a ring. This ring looks like a chair. It stays in this chair shape. This shape helps it stay stable. It is a very important part of making things.

Cyclohexane is a clear liquid. It has a smell like soap. It can catch fire easily.

This liquid helps make nylon. Nylon is a material used for many things. To make nylon, workers use cyclohexane to make two other things. These are called adipic acid and caprolactam.

Most cyclohexane is made in a factory. Scientists use a process called hydrogenation. This means they add hydrogen to a substance called benzene. They use a special helper called a Raney nickel catalyst. This helps the change happen.

If you look at the tiny parts, they form a ring. This ring is not flat like a drawing. It looks like a chair. This is called the chair conformation. The shape helps the ring stay stable. The ring can also change into a shape called a boat. This change is called a chair flip.

Cyclohexane can also be found in naphtha. Naphtha is a liquid from oil. Workers use a way to separate it called distillation. This helps them get the cyclohexane out.

Cyclohexane is a clear, flammable liquid. It has a scent that reminds people of cleaning products or detergent. This substance is very important for making things we use every day. Most of it is used to create adipic acid and caprolactam. These two things are the building blocks for nylon. Without cyclohexane, making nylon would be much harder.

There are two main ways to make cyclohexane. One way is to take it from naphtha. Naphtha is a liquid found in oil. Workers use a method called distillation to separate it. They might also use isomerization to change methylcyclopentane into cyclohexane. The other way is through industrial synthesis. In this way, workers add hydrogen to benzene. They use a helper called a Raney nickel catalyst to make this happen.

Finding the right way to make cyclohexane took a long time. Early scientists had some trouble with it. In 1867, Marcellin Berthelot tried to make it using benzene and hydroiodic acid. In 1870, Adolf von Baeyer tried a similar way. He called his result hexahydrobenzene. In 1890, Vladimir Markovnikov thought he found it in petroleum. He called his version hexanaphtene. Later, in 1895, Markovnikov, N.M. Kishner, and Nikolay Zelinsky realized those were actually different things.

Success finally came in 1894. That year, Baeyer made cyclohexane from pimelic acid. Also in 1894, E. Haworth and W.H. Perkin Jr. made it using a Wurtz reaction. Today, the liquid is used in many places. It is a solvent in some correction fluids. It is also used to help crystals grow in a process called recrystallization. Some machines use it to check their settings. It works well because it changes from a crystal to a liquid at −87.1 °C.

If you could see the tiny molecules, they would look very interesting. They do not form a flat shape like a drawing of a hexagon. Instead, they form a 3D shape called a chair conformation. This shape is the most stable way for the ring to sit. The molecules can also flip into a shape called a boat conformation. This movement is known as a chair flip. Hermann Sachse first suggested the chair shape back in 1890. This shape helps the ring stay strong and steady.

Cyclohexane is a specific type of chemical called a cycloalkane. It is a colorless, flammable liquid with a smell like detergent or cleaning products. This substance is very important to modern industry. It serves as a primary building block for making nylon. Specifically, it is used to produce adipic acid and caprolactam. These two chemicals are precursors, or starting materials, for nylon production.

There are two main ways to obtain cyclohexane for industrial use. One method involves extracting it from naphtha. Naphtha is a component of petroleum. Workers use advanced distillation to separate cyclohexane from other parts of the naphtha. They might also use isomerization to turn methylcyclopentane into cyclohexane. These extraction methods only meet about 15% to 20% of the modern demand. The rest of the world's supply comes from industrial synthesis.

Modern industrial synthesis uses a process called hydrogenation. In this process, hydrogen is added to a chemical called benzene. To make this reaction happen, producers use a Raney nickel catalyst. This catalyst helps the benzene and hydrogen react more effectively. This chemical reaction is highly exothermic. This means it releases a large amount of heat energy. In fact, the energy released is -216.37 kJ/mol at 500 K. Because of this, producers of cyclohexane account for about 11.4% of the global demand for benzene.

Finding a reliable way to make cyclohexane was a major challenge for early chemists. Unlike benzene, cyclohexane is not found in natural resources like coal. In 1867, Marcellin Berthelot tried to reduce benzene using hydroiodic acid at high temperatures. In 1870, Adolf von Baeyer repeated this and called his product "hexahydrobenzene." Later, in 1890, Vladimir Markovnikov thought he had distilled a version called "hexanaphtene" from Caucasus petroleum.

These early attempts actually resulted in a mistake. The substances they created were actually methylcyclopentane. This happened because of an unexpected rearrangement reaction. In 1895, Markovnikov, N.M. Kishner, and Nikolay Zelinsky solved this riddle by identifying the error. Real success arrived in 1894. That year, Baeyer synthesized cyclohexane through the decarboxylation of pimelic acid. At the same time, E. Haworth and W.H. Perkin Jr. prepared it using a Wurtz reaction of 1,6-dibromohexane.

Cyclohexane is used in many specialized scientific and industrial ways. It can undergo autoxidation to create a mixture called "KA oil." This mixture contains cyclohexanone and cyclohexanol. Several million kilograms of these two substances are produced every year. Cyclohexane is also used as a solvent in some correction fluids. Scientists use it as a recrystallization solvent because organic compounds dissolve well in it when it is hot. It also works well when it is cold.

Beyond making plastics, cyclohexane is used for precise scientific measurements. It is used to calibrate differential scanning calorimetry (DSC) instruments. This is possible because it has a very convenient crystal-to-crystal transition at -87.1 °C. In heavy industry, cyclohexane vapor is used in vacuum carburizing furnaces. These furnaces are used in the manufacture of heat-treating equipment.

The molecular structure of cyclohexane is quite unique. While we often draw it as a flat hexagon, it is actually a three-dimensional shape. A flat shape would cause too much strain on the chemical bonds. To reduce this torsional strain, the molecule adopts a "chair conformation." This shape allows the carbon atoms to sit at an angle of 109.5 degrees. The molecule can also undergo a "chair flip." This is a process where the molecule rapidly moves between different shapes.

During a chair flip, the molecule passes through several intermediate stages. These include the half-chair, the boat conformation, and the twist-boat. The half-chair is the most unstable state, representing an energy maximum. The boat is also a transition state. The twist-boat is more stable than the boat, but less stable than the chair. The chair and twist-boat are considered energy minima. Hermann Sachse first proposed the chair conformation idea in 1890. This shape is so stable that cyclohexane has zero total ring strain.