What Cyclohexane Is
Cyclohexane is a saturated cyclic hydrocarbon with the molecular formula C6H12 and the CAS number 110-82-7. It is a colourless, flammable liquid with a mild, sweet odour, and it is immiscible with water. Cyclohexane is a nonpolar solvent, which means it dissolves oils, fats, waxes, resins and many organic compounds while leaving polar and ionic substances largely untouched.
Commercially, cyclohexane is produced mainly by the catalytic hydrogenation of benzene. It is one of the highest-volume organic chemicals in the world because of its role as a raw material for nylon intermediates.
Cyclohexane in Nylon 6 and Nylon 6,6 Production
The largest share of cyclohexane production is consumed in the manufacture of nylon 6 and nylon 6,6 intermediates.
In the first step, cyclohexane is oxidised with air to a mixture of cyclohexanol and cyclohexanone, commonly called KA oil. The KA oil is then processed in two directions. Part of it is oxidised to adipic acid, a key monomer for nylon 6,6. Another part is converted to cyclohexanone oxime and then rearranged to caprolactam, the monomer of nylon 6.
| Intermediate | Route | Downstream polymer |
|---|---|---|
| KA oil | Air oxidation of cyclohexane | Cyclohexanol and cyclohexanone feedstock |
| Adipic acid | Oxidation of cyclohexanol and cyclohexanone | Nylon 6,6 |
| Caprolactam | Oxime formation and rearrangement | Nylon 6 |
Nylon 6 and nylon 6,6 are engineering thermoplastics used in textiles, carpets, clothing, ropes, tyre cords, fishing nets and moulded engineering parts. This value chain is why cyclohexane demand is closely linked to the textile and automotive industries.
Industrial Solvent Applications
Because cyclohexane is a strong nonpolar solvent with a narrow boiling range, it is used in several solvent duties.
Paints, varnishes and lacquers: used in specialty coatings where fast evaporation and good resin solvency are required.
Adhesives and rubber: dissolves natural and synthetic rubber and many resins, so it is used in industrial adhesives and rubber cements.
Extraction: used to extract essential oils from plant material and to dissolve oils, fats and waxes in industrial processes, with easy recovery by distillation.
Reaction medium: serves as a reaction medium where an inert, nonpolar environment is needed, and as a crystallisation solvent.
Other Derivatives and Industry Applications
Beyond nylon and solvent uses, cyclohexane is a feedstock for cyclohexanol, cyclohexanone and adipic acid, which in turn serve the production of plasticisers, coatings and pharmaceuticals. Small volumes are used in analytical chemistry as a calibration solvent and in polymerisation processes as a diluent.
Safety, Storage and Handling
Cyclohexane is highly flammable and forms explosive vapour-air mixtures at room temperature. Its vapours are heavier than air and can travel to ignition sources. Prolonged skin contact can defat the skin, and high vapour concentrations can cause dizziness and central nervous system effects.
Handling requires bonding and grounding of equipment, explosion-proof ventilation, and storage in properly labelled containers away from oxidisers and open flames. Cyclohexane is classified as a dangerous good for transport and is listed in hazardous chemical catalogues in most jurisdictions, so importers must confirm local registration and permit requirements before shipment.
Frequently Asked Questions
Q: What is the CAS number of cyclohexane?
The CAS number of cyclohexane is 110-82-7, and its molecular formula is C6H12.
Q: Is cyclohexane polar or nonpolar?
Cyclohexane is a nonpolar solvent. It dissolves oils, fats, waxes and resins but does not mix with water.
Q: Why is cyclohexane important for nylon?
Cyclohexane is oxidised to cyclohexanol and cyclohexanone, which are converted to adipic acid for nylon 6,6 and to caprolactam for nylon 6.
Q: Can cyclohexane dissolve in water?
No. Cyclohexane is essentially immiscible with water because it is a nonpolar hydrocarbon.
Q: Is cyclohexane flammable?
Yes. Cyclohexane is highly flammable with a flash point well below room temperature, and its vapours form explosive mixtures with air.
Q: How is cyclohexane produced?
Cyclohexane is produced industrially by the catalytic hydrogenation of benzene, and it is also recovered in some refinery streams.