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Heptane boils at about 98.4 °C (371.5 K, 209 °F) at normal atmospheric pressure (1 atm, 760 mmHg). That is the NIST Chemistry WebBook average for n-heptane (C7H16, CAS 142-82-5), and NOAA CAMEO Chemicals lists 209.1 °F (98.4 °C) at 760 mmHg. This page turns the number into a bench solvent datasheet: what the source values are, why they differ slightly, and what the boiling point, freezing point, density and vapor pressure mean for evaporation, extraction and chromatography. It is general reference information, not a safety data sheet; use the supplier’s SDS for handling.
Short answer: heptane boiling point
- Boiling point: 371.5 ± 0.3 K, which is 98.35 °C (NIST WebBook, average of 215 of 227 values). CAMEO Chemicals: 209.1 °F, 98.4 °C at 760 mmHg.
- Freezing/melting point: 182.6 ± 0.4 K, which is about −90.55 °C (NIST, average of 51 of 52 values). CAMEO: −131 °F, −90.6 °C.
- Density: specific gravity 0.6838 at 20 °C (CAMEO), so heptane is lighter than water.
- Flash point: 25 °F (−3.9 °C) (CAMEO), so it is a highly flammable liquid at room temperature.
Definition and scope
Heptane is a straight-chain alkane with the formula C7H16 and a molecular weight of 100.2 (NIST lists 100.2019). The boiling point is the temperature at which the liquid’s vapor pressure equals the surrounding pressure; the values on this page are for 1 atm unless stated. The related variants people search for (density, vapor pressure, freezing point) are covered below. Polarity, dielectric constant, refractive index and viscosity are not tabulated here because values should be taken from a current reference such as the CRC Handbook or the supplier’s technical data sheet, and quoted with their temperature.
Boiling point by source and unit
The same physical constant appears as 98.35, 98.4 and 209.1 in different places. That is rounding and unit conversion, not disagreement.
| Source | Value as published | In °C | Note |
|---|---|---|---|
| NIST Chemistry WebBook | 371.5 ± 0.3 K | 98.35 °C (K − 273.15) | Average of 215 of 227 reported values |
| NOAA CAMEO Chemicals | 209.1 °F at 760 mmHg | 98.4 °C | Values attributed to USCG 1999 and NIOSH 2024 |
To convert, subtract 273.15 from kelvin to get Celsius, and use °F = °C × 1.8 + 32. NIST’s ± 0.3 K shows that the third significant figure is already uncertain, so quoting 98 °C is usually enough for solvent selection.
How to calculate or convert a boiling point and melting point
For a pure, well-characterised compound you do not calculate the boiling point from first principles at the bench; you look up a measured value and convert units. The two things that change what you observe are pressure and purity. A boiling point is quoted at a stated pressure (here 760 mmHg), and under reduced pressure, as in a rotary evaporator, a solvent boils at a lower temperature. Do not apply a rule of thumb to heptane without a vapor-pressure table or an equation from a reference you trust. The melting point is read the same way: NIST gives 182.6 K for the freezing point and a triple point of 182.56 ± 0.03 K, with a heat of fusion of 14.04 kJ/mol (Domalski and Hearing, 1996), which converts to −90.5 °C.
Density and vapor pressure
Heptane density
CAMEO Chemicals lists a specific gravity of 0.6838 at 68 °F (20 °C) and describes heptane as less dense than water. Supplier labels often quote a density near 0.684 g/mL at 25 °C; always read the temperature printed beside any density value. At the bench this means heptane forms the top layer when shaken with water.
Heptane vapor pressure
CAMEO gives 37.49 mmHg at 70 °F (about 21 °C). Safety data sheets from suppliers quote slightly different figures (for example around 40 mmHg or 48 hPa at 20 °C), because the temperature, units and method differ. Vapor pressure rises steeply with temperature, so compare values only at the same temperature.
Where it matters for labs: a heptane solvent card
| Property | Value (source) | What it means at the bench |
|---|---|---|
| Boiling point | 98.4 °C at 760 mmHg (CAMEO); 371.5 K (NIST) | Higher boiling than hexane and pentane, so it evaporates more slowly; see the hexane boiling point and pentane boiling point guides to compare. |
| Flash point | −3.9 °C (CAMEO) | Vapors can ignite below room temperature; keep away from ignition sources. |
| Flammable range | LEL 1 %, UEL 7 % (CAMEO) | Vapor in air between these concentrations can burn. |
| Autoignition | 433 °F, 223 °C (CAMEO) | SDS values differ by method and supplier; use the SDS for your product. |
| Water solubility | 0.0003 % (NIOSH 2024, via CAMEO) | Practically immiscible with water, so it separates as a distinct upper layer. |
| Density | 0.6838 at 20 °C (CAMEO) | Lighter than water: the organic phase is on top. |
Because the table compares properties across the sources named, it also shows why heptane is often considered where a slower-evaporating nonpolar alkane is wanted, but any substitution of one solvent for another in a method should follow the validated method or your own validation. For other solvent property pages in this cluster see tetrahydrofuran boiling point and chloroform density.
Common misunderstandings
- “98 °C, 98.4 °C and 209 °F are different answers.” They are one value in different units and rounding.
- “The boiling point is fixed.” It is defined at a stated pressure; at lower pressure the liquid boils at a lower temperature.
- “All heptane is the same.” The numbers above are for n-heptane. Commercial products labelled heptane can be a mixture of isomers or a defined grade, and their specifications are on the supplier’s technical data sheet.
- “One SDS number is the number.” Vapor pressure and autoignition temperature vary between SDS documents because of method and temperature differences.
FAQ
What is the boiling point of heptane in Celsius?
About 98.4 °C at 1 atm (NIST 371.5 K = 98.35 °C; CAMEO 98.4 °C).
What is the freezing point of heptane?
About −90.5 °C: NIST lists 182.6 ± 0.4 K and CAMEO −90.6 °C.
Are heptane and heptane the same?
Two entries with the same name usually refer to n-heptane (the straight-chain compound, CAS 142-82-5) on one side and a commercial heptane grade on the other. Check the CAS number and the stated purity on the label before assuming the property values transfer.
How many isomers does heptane have?
The formula C7H16 has nine constitutional isomers; n-heptane is the straight-chain one. The properties on this page apply to n-heptane only.
How do I calculate a boiling point and melting point?
You normally look them up at a stated pressure and convert units (K − 273.15 = °C). Measured values from NIST or the CRC Handbook are preferred over estimates.
Is heptane polar?
Heptane is a nonpolar alkane and is practically insoluble in water (0.0003 %, NIOSH 2024 via CAMEO). For dielectric constant, refractive index and viscosity, take temperature-stated values from a current reference or the supplier’s data sheet.
Sources
- NIST Chemistry WebBook, heptane (CAS 142-82-5): webbook.nist.gov, read 2026-11-08.
- NOAA CAMEO Chemicals, n-heptane datasheet: cameochemicals.noaa.gov, read 2026-11-08.
- PubChem compound record, heptane (CID 8900), formula and molecular weight.
