What Is Adamantane?
Adamantane is a cage-shaped organic compound formed from three chair-shaped cyclohexanes.
In nature, it is a stable compound found in trace amounts in petroleum. Its name is derived from the Greek word “adamas,” meaning diamond.
Adamantane is very stable and free from distortion because it is composed of chair-shaped cyclohexane.
Properties of Adamantane
| Chemical formula | C10H16 |
| English name | Adamantane |
| Molecular weight | 136.23 |
Uses of Adamantane
Adamantane is a very stable chemical substance and is used for stabilization purposes by combining with unstable chemical species. It is characterized by excellent heat resistance, fat solubility, sublimation resistance, moisture resistance, high refractive index, and chemical resistance.
Adamantane derivatives can be used as photoresists for semiconductor manufacturing in the electronics field and as raw materials in the pharmaceutical field. For example, 1-aminoadamantane is commercially available as an antiviral agent. In addition, 1-adamantyl methacrylate derivative has been put to practical use as a monomer for photoresists in semiconductor manufacturing.
Properties of Adamantane
Adamantane is a colorless, transparent crystal that sublimates and has a camphor-like odor. Its melting point is 518°F (270°C), very high among hydrocarbons. It is virtually insoluble in water and soluble in non-polar organic solvents.
Adamantane and its derivatives undergo ionic reactions with carbocations as intermediates. For example, the reaction of antimony pentafluoride with 1-fluoro adamantane gives adamantyl ions, which are more stable than the usual tertiary ions and other carbocation.
Structure of Adamantane
The chemical formula of adamantane is C10H16, its molecular weight is 136.23, and its density at 20°C is 1.08 g/cm3. The numerical value of the molecular structure has been determined by X-ray crystallography and electron diffraction. For example, the carbon-carbon bond length (C-C) is 154 pm, approximately equal to that of a diamond. The carbon-hydrogen bond length (C-H) is 111.2 pm.
The bond angle of each carbon is close to 109.5°, which is the natural angle of sp3 carbon, and the structure of adamantane is strain-free. The crystal structure of adamantane is usually a face-centered cubic lattice. The unit lattice contains four molecules, and the molecules are oriented in various directions in the crystal.
When cooled to 208 K or pressurized to 0.5 gigapascals, it assumes a body-centered square lattice structure of two molecules in the unit lattice.
Other Information on Adamantane
1. Synthesis of Adamantane by Vladimir Prelog
Adamantane was first synthesized by Vladimir Prelog in 1941. It was a complex five-step synthesis from the starting material Meerwein’s ester, with a total yield of about 0.16%. Subsequent improvements to the synthetic method have resulted in a total yield of 6.5%.
2. Synthesis of Adamantane by Paul von Ragué Schleyer
In 1957, Paul von Ragué Schleyer accidentally discovered a simple method for the synthesis of adamantane. First, dicyclopentadiene is hydrogenated in the presence of a catalyst such as a platinum oxide to obtain tetrahydrodicyclopentadiene.
Then, when heated with a Lewis acid such as aluminum chloride, the hydride is withdrawn and the resulting carbocation is successively rearranged. Finally, a stable adamantane skeleton can be produced.
Initial yields were 30-40%, but have since increased to 60%. It is also an efficient method of supplying adamantane, and the process is still used in laboratories today.