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Cyclohexane boils at 80.7 °C (353.9 K, about 177 °F) at 760 mmHg. NIST gives 353.9 ± 0.2 K as an average of published values, and PubChem lists 80.7 °C (Merck Index 2013), 80.73 °C and 81 °C from different sources. Cyclohexane (C6H12, CAS 110-82-7) is a nonpolar, highly flammable hydrocarbon solvent. This page is a bench datasheet: the numbers, where each comes from, and what they mean for evaporation, storage and extraction.
Values by source
The small spread in the boiling point comes from rounding and from different compilations, not from different chemistry. All values below are at normal pressure (760 mmHg).
| Source | Boiling point |
|---|---|
| NIST Chemistry WebBook (average of 93 of 116 values) | 353.9 ± 0.2 K (80.75 °C) |
| Merck Index, 2013 (via PubChem) | 80.7 °C |
| PAC/DOE (via PubChem) | 80.73 °C |
| ILO-WHO ICSC (via PubChem) | 81 °C |
| NIOSH, OSHA (via PubChem) | 177 °F |
For a lab notebook, 80.7 °C is the figure to quote; 81 °C is common in safety documents that round.
Pressure and vapor pressure
The boiling point is the temperature at which vapor pressure equals the surrounding pressure, so it moves with the vacuum you pull. NIST publishes Antoine constants for cyclohexane in the form log10(P) = A – B / (T + C), with P in bar and T in kelvin. The Willingham (1945) set, valid 293.06 to 354.73 K, is A = 3.96988, B = 1203.526, C = -50.287.
Applying that equation (our own calculation from the NIST constants):
| Temperature | Calculated vapor pressure |
|---|---|
| 25 °C (298.15 K) | 0.130 bar, about 98 mmHg |
| 40 °C (313.15 K) | 0.246 bar, about 185 mmHg |
| 50 °C (323.15 K) | 0.362 bar, about 272 mmHg |
| 60 °C (333.15 K) | 0.519 bar, about 389 mmHg |
| 80.75 °C (353.9 K) | 1.01 bar, about 760 mmHg |
The 25 °C result agrees with the experimental values PubChem reports: 13.0 kPa (CRC Handbook, 76th ed.), 96.9 mmHg (Chao 1983) and 95 mmHg (NTP). The Gaw and Swinton (1968) constants (303 to 343 K: A = 3.9920, B = 1216.93, C = -48.621) give the same pressures within about 0.1 percent across this range, a useful consistency check.
Cyclohexane vapor pressure in practice
A vapor pressure near 0.13 bar at room temperature means cyclohexane evaporates readily on an open bench. The same calculation shows how vacuum evaporation works for it: with a 40 °C bath, a vacuum of roughly 185 mmHg or lower brings the solvent to its boiling point; deeper vacuum boils it faster or lets you use a cooler bath. Treat these as starting points derived from the equation, not a validated method; condenser temperature and flask loading change real behavior.
Related properties
| Property | Value | Source |
|---|---|---|
| Density | 0.7781 g/mL at 20/4 °C; 0.7739 at 25 °C | Merck Index, 2013 (PubChem) |
| Freezing / melting point | 6.47 °C (279.6 ± 0.3 K) | Merck Index (PubChem); NIST WebBook |
| Refractive index | 1.42662 at 20 °C (D line) | CRC Handbook, 94th ed. (PubChem) |
| Viscosity | 0.977 mPa·s at 20 °C | Ullmann’s, Campbell 2011 (PubChem) |
| Water solubility | 55 mg/L at 25 °C | Yalkowsky 2010 (PubChem) |
| Flash point | about -20 °C; -18 °C closed cup | NTP; Merck Index (PubChem) |
| Heat of vaporization | 33.1 ± 0.4 kJ/mol | NIST WebBook |
| Critical point | 554 ± 1 K, 40.7 ± 0.5 bar | NIST WebBook |
Cyclohexane density
At 20 °C cyclohexane is about 0.778 g/mL, well below water, so as a water-insoluble liquid it forms the upper layer in a separatory funnel. For comparison with other solvents see the site’s pages on acetone density, ethyl acetate density and diethyl ether density.
Cyclohexane polarity, polarity index and dielectric constant
Cyclohexane is a saturated hydrocarbon ring with no polar functional group, so it is a nonpolar solvent. With a water solubility of only 55 mg/L it is effectively immiscible with water.
Cyclohexane pKa
Cyclohexane has no ionizable group, so it has no practical pKa in water.
Cyclohexane freezing point
Freezing at about 6.5 °C means cyclohexane can solidify in a cold room or a 4 °C refrigerator, which surprises people used to liquid solvents.
At the bench
- Comparison with neighbors. Compare its 80.7 °C boiling point with hexane and toluene when choosing a solvent you must later remove.
- Flammability. A flash point near -20 °C means vapor can ignite well below room temperature. Keep it away from ignition sources and follow your institution’s flammable-liquid storage rules and the safety data sheet.
- Extraction. Low water solubility and a density below water give a clean upper organic layer.
- Cold storage. Because it freezes near 6.5 °C, check containers stored cold before assuming a clear liquid.
Common misunderstandings
- “The boiling point is a constant.” It is the value at 760 mmHg; it falls under vacuum, as the Antoine table shows.
- “Different sources disagree.” 80.7, 80.73, 80.75 and 81 °C are the same quantity at different rounding.
- “Cyclohexane never freezes in a lab.” Its freezing point is about 6.5 °C.
FAQ
What is the boiling point of cyclohexane in Celsius?
80.7 °C at 760 mmHg (Merck Index 2013); NIST’s averaged value is 353.9 K, or 80.75 °C.
What is the vapor pressure of cyclohexane?
About 13.0 kPa (roughly 97 mmHg) at 25 °C per the CRC Handbook and Chao (1983) values reported by PubChem.
Is cyclohexane soluble in water?
Barely. Reported solubility is 55 mg/L at 25 °C (Yalkowsky 2010).
What is the freezing point of cyclohexane?
About 6.5 °C (6.47 °C per the Merck Index; 279.6 K per NIST).
General reference information, not safety or medical advice. Consult the supplier’s safety data sheet before handling.
Sources
- NIST Chemistry WebBook, Cyclohexane, CAS 110-82-7: webbook.nist.gov (read 2026-11-07).
- PubChem, Cyclohexane, CID 8078, experimental properties: pubchem.ncbi.nlm.nih.gov (read 2026-11-07).
