PETROLEUM ETHER OR BENZINE: FORMULA, STRUCTURE, USES - CHEMISTRY - 2025

The petroleum ether or benzene is a distillation fraction of oil. Its boiling point ranges between 40ºC and 60ºC. It is considered economically important because it is made up of five-carbon (pentane) and six-carbon (hexane) aliphatic hydrocarbons, with little presence of aromatic hydrocarbons.

The name of petroleum ether is due to its origin, and to the volatility and lightness of the compound that resembles it to ether. However, ethyl ether has a molecular formula (C ₂ H ₅) O; whereas petroleum ether has a molecular formula: C ₂ H _{2n + 2}. Therefore, it can be said that petroleum ether is not an ether in itself.

Bottle with petroleum ether. Source: Seilvorbau / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Petroleum ether is grouped into compounds with boiling points between 30-50 ° C, 40-60 ° C, 50-70 ° C and 60-80 ° C. It is an efficient non-polar solvent for dissolving fats, oils and wax. In addition, it is used as a detergent and fuel, as well as in paints, varnishes, and in photography.

Formula and structure

Petroleum ether is not a compound: it is a mixture, a fraction. This is composed of aliphatic hydrocarbons, which have a general molecular formula C ₂ H _{2n + 2}. Their structures are based solely on CC and CH bonds, and on a carbon skeleton. Therefore, this substance has no chemical formula formally speaking.

None of the hydrocarbons that make up petroleum ether, by definition logically, have oxygen atoms. Thus, not only is it not a compound, it is also not an ether. It is referred to as an ether for the simple fact of having a similar boiling point to that of ethyl ether; the rest do not bear any similarity.

Petroleum ether is made up of linear, short-chain aliphatic hydrocarbons, type CH ₃ (CH ₂) _x CH ₃. Being of low molecular mass, it is not surprising that this liquid is volatile. Its nonpolar character due to the absence of oxygen or some other heteroatom or functional group makes it a good solvent for fats.

Properties

Appearance

Colorless or slightly yellowish, translucent and volatile liquid.

Other names for light petroleum

Hexane, benzine, naphtha and ligroin.

Molar mass

82.2 g / mol

Density

0.653 g / mL

Melting point

-73 ºC

Boiling point

42 - 62 ºC

Water solubility

Insoluble. This is because all of its components are apolar and hydrophobic.

Vapor pressure

256 mmHg (37.7 ° C). This pressure corresponds to almost a third of atmospheric pressure. As such, petroleum ether is a less volatile substance compared to butane or dichloromethane.

Vapor density

3 times that of air

Refractive index (nD)

1,370

ignition point

Autoignition temperature

246.11 ºC

Applications

Solvents

Petroleum ether is a nonpolar solvent used in dry cleaners to dissolve grease, oil, and wax stains. It is also used as a detergent, fuel and insecticide, as well as being present in paints and varnishes.

It is used to clean stationery, carpets and tapestries. It is also used to clean engines, automotive parts and all kinds of machines.

Dissolves and removes gum from self-adhesive stamps. Therefore, it is part of the tag remover products.

Chromatography

Petroleum ether is used in conjunction with acetone in the extraction and analysis of plant pigments. Acetone performs the extraction function. Meanwhile, petroleum ether has a high affinity for pigments, so it acts as a separator in their chromatography.

Pharmaceutical industry

Petroleum ether is used in the extraction of stigmasterol and β-sitosterol from a plant of the genus Ageratum. Stigmasterol is a plant sterol, similar to cholesterol in animals. This is used as a precursor to the semisynthetic hormone progesterone.

Petroleum ether is also used in the extraction of immunomodulatory substances from an herb, known as the pyrethrum of Anacyclus. On the other hand, with it an extract of myrrh with anti-inflammatory activity is obtained.

Advantage

In many cases, petroleum ether is used in the extraction of natural products from plants as the sole solvent. This reduces extraction time and process costs, since petroleum ether is less expensive to produce than ethyl ether.

It is an apolar solvent that is not miscible with water, so it can be used for the extraction of natural products in plant and animal tissues with high water content.

Petroleum ether is less volatile and flammable than ethyl ether, the main solvent used in the extraction of natural products. This determines that its use in extraction processes is less risky.

Risks

Inflammability

Petroleum ether is a liquid that, like its vapors, are highly flammable, so there is a risk of explosions and fires during handling.

Exposition

This compound acts deleteriously on various organs considered as targets; such as the central nervous system, lungs, heart, liver and ear. It can be fatal if swallowed and enters the respiratory tract.

It is capable of producing skin irritation and allergic dermatitis, caused by the degreasing action of the solvent. It also causes eye irritation when it comes into contact with the eyes.

Ingestion of petroleum ether can be fatal, and ingestion of 10 mL is thought to be sufficient to cause death. Pulmonary aspiration of ingested ether causes damage to the lungs, which can even lead to pneumonitis.

The action of petroleum ether on the central nervous system manifests itself with headaches, dizziness, fatigue, etc. Petroleum ether causes kidney damage, manifested by the urinary excretion of albumin, as well as hematuria, and an increase in the presence of liver enzymes in plasma.

Excessive exposure to petroleum ether vapors can cause irritation of the respiratory tract, with the same consequences as ingesting the solvent. Experiments with rats do not indicate that petroleum ether has a carcinogenic or mutagenic action.

References

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