What Is Cyclooctatetraene?
Cyclooctatetraene (COT), with the molecular formula C8H8, is a cyclic unsaturated hydrocarbon, and a member of the annulenes, specifically [8]annulene. Its CAS number is 629-20-9. This compound, a colorless or pale yellow liquid at room temperature, is known for its distinct odor and is insoluble in water but soluble in organic solvents like ether, benzene, and ethanol.
With a molecular weight of 104.149, COT has a melting point of -3 °C and a boiling point of 143 °C. It is slightly hygroscopic and gradually polymerizes in air.
Uses of Cyclooctatetraene
COT is used in the synthesis of organic films for silicon surfaces, liquid-state organic dye lasers, and as a triplet-state quencher. It’s a valuable synthetic intermediate for various cyclic compounds and raw material for chemicals like terephthalaldehyde and phenylacetaldehyde.
Synthesis and Chemical Properties of Cyclooctatetraene
1. Synthesis of Cyclooctatetraene
COT is synthesized via Reppe synthesis, involving the polymerization of acetylene in tetrahydrofuran using nickel cyanide as a catalyst under high pressure. It was first synthesized from natural pelletierine by Richard Willstätter in 1912.
2. Chemical Properties of Cyclooctatetraene
COT is an 8π electron system and is non-aromatic, as it doesn’t adhere to the Hückel rule for aromaticity. It adopts a boat conformation and is reactive to addition, rearrangement, and oxidation reactions. Interestingly, reactions like those with potassium can convert COT from non-aromatic to aromatic, forming a dianion that satisfies the Hückel rule.
Types and Storage of Cyclooctatetraene
COT is primarily used as a research reagent and is available in small quantities, typically sold in glass bottles and requiring refrigerated or frozen storage. It often contains a small percentage of polymerization inhibitors like hydroquinone due to its propensity to polymerize.
Related compounds like cyclooctatetraene iron tricarbonyl, where COT acts as an iron ligand, are also marketed for research and development purposes.