Cyclohexene

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Cyclohexene is a simple hydrocarbon with the formula C6H10. It is a cycloalkene, meaning its six-membered ring contains one carbon–carbon double bond. At room temperature it is a colorless liquid with a sharp odor. It is an important intermediate in the production of nylon and other chemicals.

How it’s made
- In industry, cyclohexene forms mainly during the partial hydrogenation of benzene. The main product is cyclohexane, but some cyclohexene is also produced because the hydrogenation of benzene is not complete.
- In the laboratory, cyclohexene can be prepared by dehydrating cyclohexanol.

Structure and stability
- The ring prefers a half-chair shape. The double bond is planar, so that part of the ring is flat while the rest of the ring bends.

Key reactions and uses
- Hydration: Adding water to cyclohexene gives cyclohexanol, which can be turned into cyclohexanone, a building block for caprolactam and thus for nylon.
- Alkylation: Cyclohexene reacts with benzene in the presence of an acid catalyst to form cyclohexylbenzene, a precursor to phenol and to cyclohexanone.
- Oxidation: With hydrogen peroxide and a tungsten catalyst, cyclohexene can be oxidized to adipic acid, another nylon precursor.
- Bromination: Adding bromine across the double bond gives 1,2-dibromocyclohexane.
- Ethenolysis: Cyclohexene can be converted to 1,7-octadiene through ethenolysis.
- Hydrogenation context: Cyclohexene hydrogenates more readily than benzene, so during benzene hydrogenation, cyclohexane is often the main product.

Physical properties
- Density: about 0.811 g/cm3
- Boiling point: about 83 °C
- Melting point: about -103.5 °C
- Solubility: slightly soluble in water; miscible with organic solvents
- Appearance: colorless liquid with a sharp odor
- It is flammable and should be handled with care in a well-ventilated area.

Safety note
- Cyclohexene is hazardous and flammable. Use proper protective equipment and work in a suitable environment to avoid inhalation or skin contact.