Petroleum ether is a common, colorless, and volatile liquid used widely in laboratory and industrial settings as a solvent. It is a petroleum distillate, separated from crude oil through a refining process. Despite its misleading name, petroleum ether is not a true ether (a class of organic compounds containing oxygen). The name stems from its high volatility and strong solvent power, which historically resembled that of diethyl ether. It functions as a highly effective nonpolar solvent.
Chemical Identity and Composition
Petroleum ether is chemically defined as a complex mixture of low-boiling aliphatic hydrocarbons. It is obtained through the fractional distillation of crude petroleum, a process that separates components based on their different boiling points. The final product is not a single compound but a blend of saturated chain-like molecules known as alkanes.
The primary constituents are typically pentanes and hexanes, though some grades may include heptanes depending on the specific distillation cut. This composition makes the solvent largely non-polar, dictating its ability to dissolve substances. The mixture usually contains minimal amounts of aromatic hydrocarbons, such as benzene, which is often reduced in modern formulations for safety concerns.
Physical Properties and Grades
Physically, petroleum ether is a clear, colorless liquid with an odor similar to gasoline or kerosene. It is highly volatile, evaporating rapidly at room temperature due to its low-molecular-weight hydrocarbon makeup. This volatility is a key feature, making it desirable in applications where quick drying is necessary.
The product is categorized and sold according to its specific boiling range, which indicates its average composition and volatility. Common commercial grades include 30–60°C, 40–60°C, 60–80°C, and 90–120°C. Lower boiling ranges indicate a more volatile solvent dominated by pentanes and hexanes. Petroleum ether is immiscible with water but readily mixes with most other organic solvents.
Primary Applications as a Solvent
The primary function of petroleum ether is its use as an inexpensive, non-polar solvent, making it highly effective for dissolving substances like fats, oils, and waxes. In laboratories, it is frequently used in extraction processes to isolate lipids from biological materials or natural products.
It is a standard component in analytical chemistry, serving as a mobile phase in chromatographic techniques. Its non-polar nature allows it to separate complex mixtures into their constituent non-polar compounds. Industrially, the solvent serves as an effective degreasing agent in the automotive and metalworking sectors. It is also incorporated into the formulation of various commercial products, including paints, varnishes, and adhesives, where it acts as a diluent and solvent.
Safety and Handling Considerations
Petroleum ether presents an extreme flammability hazard. The vapors are heavier than air and can travel along the ground to distant ignition sources, creating a serious fire and explosion risk. All handling must take place in an area free from open flames, sparks, or hot surfaces. This requires the use of explosion-proof electrical equipment and non-sparking tools.
Strict ventilation, ideally using a local exhaust system or chemical fume hood, is necessary to keep vapor concentrations below exposure limits. Inhalation of high concentrations can cause central nervous system effects, such as dizziness, headache, and nausea. Prolonged or repeated skin contact should be avoided by wearing solvent-resistant gloves and protective clothing, as it can cause irritation.
Storage requires keeping the container tightly closed in a cool, well-ventilated, and segregated area designed for flammable liquids. It must be kept away from incompatible materials like strong oxidizers.