Hexane: A Mixture of Isomers

Hexane is a six-carbon alkane (C₆H₁₄), commonly used as a non-polar solvent in laboratories and industry. What many people refer to simply as "hexane" is often not pure n-hexane, but rather a mixture of isomers — different structural forms with the same molecular formula but different atomic arrangements.

This mixture of hexane isomers is widely used for its solvency power, low cost, and relatively low toxicity compared to other solvents. However, certain isomers (notably n-hexane) have specific health concerns that require careful handling.

Molecular Formula and Isomerism

• Molecular Formula: C₆H₁₄

• Molar Mass: 86.18 g/mol

• Number of Isomers: 5 structural isomers

The 5 Main Structural Isomers of Hexane:

Name	Structure (skeletal)	Description
n-Hexane	CH₃–(CH₂)₄–CH₃	Straight-chain
2-Methylpentane	CH₃–CH(CH₃)–CH₂–CH₂–CH₃	Branched at carbon 2
3-Methylpentane	CH₃–CH₂–CH(CH₃)–CH₂–CH₃	Branched at carbon 3
3-Ethylbutane	CH₃–CH₂–CH(CH₂CH₃)–CH₃	Rare; least common
2,3-Dimethylbutane	CH₃–CH(CH₃)–CH(CH₃)–CH₃	Highly branched

 

Physical Properties Overview

Isomer	Boiling Point (°C)	Density (g/cm³ @ 20°C)
n-Hexane	68.7	0.659
2-Methylpentane	60.3	0.664
3-Methylpentane	63.3	0.666
3-Ethylbutane	~53–55	~0.675
2,3-Dimethylbutane	58.0	0.670

 

As branching increases, boiling point decreases due to weaker London dispersion forces.

Commercial "Hexane" Mixture

• Often contains 45–60% n-hexane, with the rest being branched isomers.

• Sold as "technical grade hexane" or "hexanes"

• Used when exact isomer identity isn’t critical, such as in:

  • Oil extraction (e.g., from soybeans)

  • Rubber and adhesive manufacturing

  • Cleaning and degreasing agents

  • Chromatography (especially non-polar solvent systems)

Applications

1. Solvent in Laboratories:

   • Used in recrystallization, extraction, and chromatography (especially TLC and column).

2. Industrial Use:

   • Vegetable oil extraction (e.g., soybean processing)

   • Adhesive and glue manufacturing

   • Leather processing, printing, and rubber cement

3. Fuel Component:

   • Found in gasoline blends as a volatility enhancer.

Health and Safety Considerations

While the hexane isomer mixture is generally less hazardous than other solvents, n-hexane in particular poses neurological risks with prolonged exposure.

• Acute exposure: Dizziness, nausea, irritation

• Chronic exposure (especially to n-hexane):

  • Can cause peripheral neuropathy

  • Symptoms: Numbness, muscle weakness, blurred vision

Safety precautions:

• Use in ventilated areas

• Wear gloves and goggles

• Store away from heat and open flames (highly flammable)

Environmental Impact

• Hexane is a volatile organic compound (VOC)

• Contributes to ground-level ozone and air pollution

• Should be disposed of as hazardous waste — avoid releasing into drains or soil

Summary Table

Feature	Description
Formula	C₆H₁₄
Type	Alkane (saturated hydrocarbon)
Isomers	5 structural isomers
Common Use	Solvent, extraction, fuel additive
Commercial Product	Mixture of isomers (hexanes)
Health Hazard	n-Hexane: neurotoxic with long-term exposure
Environmental Risk	VOC; air pollutant

 

Final Thoughts

Hexane mixtures are essential solvents in both industrial and research environments, thanks to their low reactivity, volatility, and effective solvency. However, the presence of n-hexane demands attention to safety and exposure limits, especially in food or occupational settings.

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