Hexane vs Heptane: Alkane Solvent Comparison

n-Hexane (C6H14) and n-heptane (C7H16) are straight-chain alkane hydrocarbons commonly used as non-polar solvents in laboratories and industry. While chemically similar, they differ in evaporation rate, toxicity, and regulatory status. This comparison helps you select the appropriate alkane solvent for your application.

View Hexane (n-Hexane) Details View Heptane (n-Heptane) Details

Property Comparison

Property	Hexane (n-Hexane)	Heptane (n-Heptane)
Chemical Formula	C6H14	C7H16
Boiling Point	68.7 °C	98.4 °C
Evaporation Rate (n-BuAc=1)	~8.3 (very fast)	~4.0 (fast)
Flash Point	-22 °C	-4 °C
Density	0.659 g/mL	0.684 g/mL
PEL (OSHA)	500 ppm TWA	500 ppm TWA
Neurotoxicity	High — causes peripheral neuropathy (n-hexane)	Low — minimal neurotoxic potential
Toxic Metabolite	2,5-Hexanedione (neurotoxic)	None known
Vapor Pressure	17.6 kPa at 20 °C	6.1 kPa at 20 °C
Octane Rating	~25 (poor fuel)	0 (reference standard for octane scale)

Safety Comparison

The most critical safety difference is neurotoxicity. n-Hexane is metabolized to 2,5-hexanedione, which causes progressive peripheral neuropathy (nerve damage in hands and feet) with chronic occupational exposure. This is a well-documented hazard in the shoe manufacturing and printing industries. Heptane has no known neurotoxic metabolites and is considered significantly safer for chronic exposure. Both are highly flammable (Class IA flammable liquids) with very low flash points. Both have the same OSHA PEL (500 ppm), but this is misleading — the IDLH for hexane is 5,000 ppm, and for heptane it's 750 ppm, suggesting heptane is more acutely dangerous at very high concentrations. Both are CNS depressants at high concentrations. Both require explosion-proof equipment and bonding/grounding during transfer.

Uses Comparison

n-Hexane is widely used as a solvent for oil extraction (vegetable oils, seed oils), laboratory chromatography (HPLC, GC), and as a reaction solvent in polymer synthesis. It's also used in the production of adhesives, printing inks, and rubber cement. However, its use is declining due to neurotoxicity concerns. Heptane is the preferred solvent for applications where slower evaporation is beneficial — it's used in brush-applied coatings, adhesives, and as a laboratory solvent for extractions and recrystallizations. Heptane is also the zero-point reference for the octane rating scale (iso-octane = 100, n-heptane = 0). In the lab, hexane is more common for TLC and column chromatography due to its faster evaporation; heptane is preferred for UV spectroscopy due to its higher UV cutoff.

Verdict

Bottom Line: Choose heptane over hexane whenever possible — heptane has no neurotoxic metabolite, has a slower evaporation rate (better for many applications), and is generally safer for chronic exposure. The only advantage of hexane is its lower cost and faster evaporation (useful for quick-dry applications). For laboratory use, many labs are switching from hexane to heptane for chromatography to reduce neurotoxicity risk. For industrial extraction, hexane remains more common due to cost and proven performance, but heptane-based alternatives are available.

Frequently Asked Questions

Why is n-hexane neurotoxic but heptane is not?

n-Hexane is metabolized by cytochrome P450 to 2-hexanol, then to 2,5-hexanedione via successive oxidations. 2,5-Hexanedione is a gamma-diketone that reacts with neurofilament proteins, causing cross-linking and axonal degeneration. Heptane's metabolism produces 2,5-heptanedione, which is a gamma-diketone with a longer carbon chain that is less reactive with neurofilament proteins.

Can I substitute heptane for hexane in chromatography?

Yes — heptane can replace hexane in most chromatography applications. The main difference is slower elution (heptane is slightly less polar than hexane) and slower evaporation. For TLC, hexane is preferred for faster development. For column chromatography, heptane gives better separation for some compounds.

Is 'hexane' from the hardware store the same as n-hexane?

No — commercial 'hexane' is a mixture of hexane isomers (n-hexane, 2-methylpentane, 3-methylpentane, methylcyclopentane, etc.). The neurotoxic component is specifically n-hexane. Mixtures typically contain 20–60% n-hexane, reducing but not eliminating neurotoxicity risk. Always check the MSDS for n-hexane content.

Which is better for essential oil extraction?

n-Hexane is the traditional solvent for oilseed extraction (soybean, canola) because it's cheap, evaporates completely, and has excellent oil solubility. However, residual hexane in food products is regulated. Heptane can be used similarly but is more expensive. For small-scale essential oil extraction, ethanol or CO2 extraction are preferred over both.

Explore Chemical Details

CAS 111-27-3

Hexane (n-Hexane) (C6H14)

n-hexane, normal hexane, hexyl hydride

CAS 142-82-5

Heptane (n-Heptane) (C7H16)

n-heptane, dipropyl methane, heptyl hydride