HEXANE (C6H14): PHYSICAL AND CHEMICAL PROPERTIES, STRUCTURE, USES, TOXICITY - CHEMISTRY - 2025

The hexane is a hydrocarbon which is characterized by being an organic compound whose chemical formula is condensed C ₆ H ₁₄. It is a colorless, transparent liquid that cannot be mixed with water. It has five isomers, the linear one being one of the most important paraffinic hydrocarbons in industry and research.

Hexane is obtained by fractional distillation of crude oil. Likewise, it is naturally present in citrus fruits and in volatile fractions of various plants or fruits such as apple, guava, roasted hazelnuts, sweet potato and sage.

N-hexane molecule. Source: Benjah-bmm27

It is a highly flammable volatile liquid found in gasoline, quick-drying glues, and rubber cement. Hexane is used as a solvent in the extraction process of vegetable oils, as well as lipids and fats present in contaminated water and soils.

People who are professionally exposed to hexane may experience peripheral nervous system damage, manifested by tingling and cramps in the legs and arms; in addition to generalized muscle weakness and, in severe cases, skeletal muscle atrophy.

Physical and chemical properties of hexanes

Physical appearance

Colorless, transparent and highly volatile liquid.

Molar mass

86.178 g / mol

Odor

Similar to gasoline

Odor threshold

1.5 ppm

Density

0.6606 g / mL

Melting point

-96 to -94 ºC

Boiling point

68.5 to 69.1 ºC

ignition point

-22 ºC (closed cup).

Water solubility

9.5 mg / L (practically immiscible with water)

Solubility in solvents

Very soluble in ethanol, soluble in ethyl ether and chloroform. Miscible with alcohol, chloroform and ether.

Relative vapor density with air

2.97 (air = 1)

Octanol / water partition coefficient

Log P = 3,764

Vapor pressure

17.60 kPa at 20 ºC

Wavelength of maximum optical density

200 nm

Refractive index

1,375

Viscosity

0.3 mPa s

Caloric capacity

265.2 J K ^-1 mol ^-1

Heat of combustion

4,163.2 kJ mol ^-1

Heat of vaporization

31.56 kJ mol ^-1

Surface tension

17.89 mN / m at 25 ºC

Ionization potential

10.18 eV

Stability

Stable. Incompatible with oxidizing agents, chlorine, fluorine, magnesium perchlorate. Forms an explosive mixture with air.

Reactivity

Hexane can react vigorously with oxidizing materials, which can include liquid chlorine, concentrated oxygen, sodium hypochlorite, and calcium hypochlorite. It is also incompatible with dinitrogen tetroxide. Hexane can attack some forms of plastics, rubber, and coatings.

Structure of hexane

Intermolecular interactions

The first image shows the n-hexane molecule represented by a spheres and bars model. The black spheres correspond to the carbon atoms, making up the zigzagging carbon skeleton, while the white spheres are the hydrogen atoms. The n-hexane is therefore a hydrocarbon, linear and highly dynamic.

Because all of its CH bonds are of low polarity, the molecule lacks a dipole moment. In doing so, their intermolecular interactions are not of the dipole-dipole type, but depend exclusively on molecular mass and London dispersive forces.

Each n-hexane molecule "fits" one on top of the other at very low temperatures, as would be assumed in its crystalline structure. On the other hand, in the liquid their skeletons flex and rotate their CH bonds, causing said liquid to be volatile and boil at 68.7 ºC.

Isomers

The five isomers of hexane. Source: Steffen 962

The hydrocarbon hexane actually consists of five isomers, with n-hexane being the least branched, (1). The other four isomers are, in increasing order:

2-methylpropane (2)

3-methylpropane (3)

2,2-dimethylbutane (4)

2,3-dimethylbutane (5)

Also note that the structures become more branched from (1) to (5). Being more branched, the dispersive forces decrease, since there are no longer linear portions that wedge efficiently. This leads to a decrease and variation in the boiling points of the isomers; although some acceptable discrepancies are observed.

Both 2-methylpropane (bp = 60.3 ° C) and 3-methylpropane (bp = 63.3 ° C) are equally branched, but their boiling points are different. Then it is followed by 2,3-dimethylbutane (peb = 58 ºC), to finally locate 2,2-dimethylbutane as the most volatile liquid (peb = 49.7 ºC).

Applications

Hexane is mixed with similar chemicals to produce solvents. Among the names given to these solvents are commercial hexane, mixed hexanes, etc. They are used as cleaning agents in the textile, furniture and gravure printing industries.

Hexane is an ingredient in glues used to waterproof roofs, footwear, and leather. It is also used for binding books, for molding pills and tablets, canning, making tires and baseballs.

Hexane is used in the determination of the refractive index of minerals and filling liquid for thermometers instead of mercury; usually with a red or blue tint. It is also used in the extraction of fat and oil from water for the analysis of its contaminants.

Hexane is used as a solvent in the extraction of oil from vegetable seeds, such as soybeans, canola, or blackberry. In addition, it is used to degrease parts of different origins. It is used in the denaturation of alcohol, in the HPLC analysis method and in spectrophotometry.

Toxicity

Inhalation and contact

The acute toxicity of hexane is relatively low, although it is a mild anesthetic. Acute exposure to high concentrations of hexane can produce, by inhalation, mild central nervous system (CNS) depression, manifested by dizziness, vertigo, mild nausea, and headache.

It can also cause dermatitis and irritation of the eyes and throat. Chronic inhalation of hexane, related to work activity, can cause damage to the peripheral nervous system (sensorimotor polyneuropathy).

Initial symptoms are tingling and cramps in the legs and arms, followed by muscle weakness. In severe cases, skeletal musculature atrophy may occur, along with loss of coordination and vision problems.

The toxicity of hexane is related to the generation of the hexane-2,5-dione metabolite. This reacts with the amino acid lysine of a protein side chain, causing loss of protein function.

Safe dose

The Enviromental Protection Agency (EPA) calculated a reference concentration (RfC) for hexane of 0.2 mg / m ³, and a reference dose (RfD) of 0.06 mg / kg of body weight / day.

In the 1960s and 1970s, a group of workers in the shoemaking industry in Japan had the presence of nervous disorders. The reason was that they breathed in a 500 - 2,500 ppm hexane atmosphere for 8-14 hours per day.

The workers exhibited the known symptoms of chronic inhalation of hexane, discovering the doctors that the nerves that controlled the muscles of the arms and legs were damaged.

References

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2. National Center for Biotechnology Information. (2019). Hexane. PubChem Database. CID = 8058. Recovered from: pubchem.ncbi.nlm.nih.gov
3. Wikipedia. (2019). Hexane. Recovered from: en.wikipedia.org
4. World of Molecules. (sf). Hexane molecule. Recovered from: worldofmolecules.com
5. Chemical Book. (2017). Hexane. Recovered from: chemicalbook.com
6. Commonwealth of Australia. (sf). n-Hexane: Sources of emissions. Recovered from: npi.gov.au
7. EPA. (2000). Hexane.. Recovered from: epa.gov
8. Agency for Toxic Substances and Disease Registry. (1999). Public Health Statement for n-Hexane. Recovered from: atsdr.cdc.gov