Hexane

Description

The hexane that are commonly used in organic chemistry are a mixture of various six carbon alkanes, not just n-hexane. The lower toxicity and flammability of heptane has led to a slow shift towards heptane in favor of hexane.

Chemical properties

n-Hexane is a highly flammable liquid typically derived from crude oil and widely used as an industrial solvent, including in adhesive bandage manufacturing. It is highly toxic to both animals and humans, causing adverse health effects such as nausea, skin irritation, dizziness, limb numbness, CNS depression, vertigo, and respiratory tract irritation. Occupational exposure has been linked to motor polyneuropathy in workers, with long-term exposure—such as in glue sniffing—associated with degenerative damage to axons and nerve terminals.

Chemical properties

n-Hexane is a highly flammable, colorless, and volatile liquid with a gasoline-like odor. Its odor threshold is 0.0064 mg/L in water and 230,875 mg/m3 in air.

The Uses of Hexane

To  a solution of the SM (1.12 g, 6.66  mmol) in dry ether (19 mL) at 0 C  was added dropwise PBr3 (0.626 mL, 6.66 mmol). The ice bath was removed and the reaction was stirred for 3  h. H2O was carefully added to the mixture and the layers were  separated. The org layer was washed with brine, dried (MgSO4), and  concentrated in vacuo to provide the product. [1.49 g, 97%]

General Description

A clear, colorless liquid with a petroleum-like odor and a flash point of -9°F. It is less dense than water and insoluble in water, with vapors heavier than air. It is used as a solvent, paint thinner, and chemical reaction medium.

Reactivity Profile

n-Hexane may be sensitive to light and prolonged heat exposure. It reacts vigorously with oxidizing materials, including liquid chlorine, concentrated oxygen, sodium hypochlorite, and calcium hypochlorite, and is incompatible with dinitrogen tetroxide. Additionally, it can degrade certain forms of plastics, rubber, and coatings.

Health Hazard

n-Hexane is a respiratory irritant and narcotic at high concentrations, with acute toxicity greater than n-pentane. Short-term exposure can cause convulsions and death in animals, while humans may experience hallucinations, distorted vision, headache, dizziness, nausea, and eye/throat irritation after 10 minutes at around 5000 ppm. Chronic exposure may lead to polyneuritis. Its metabolites, 2,5-hexanedione and 5-hydroxy-2-hexanone, are shared with methyl butyl ketone, but the neurotoxic metabolite 2,5-hexanedione is produced less extensively. Continuous exposure to 250 ppm induces neurotoxic effects in animals, and occupational exposure to 500 ppm may cause polyneuropathy. Additionally, n-hexane vapor has shown reproductive toxicity in rats and mice.

Potential Exposure

n-Hexane is an industrial chemical used as an emulsifier in the production of plastics and resins, as a solvent—particularly for extracting edible fats and oils—as a laboratory reagent, and as a filling fluid in low-temperature thermometers. Technical and commercial grades typically contain 45–85% n-hexane, along with cyclopentane, isohexane, and 1–6% benzene.

Source

n-Hexane is a component of gasoline, accounting for 1.2% of hydrocarbons in diesel engine exhaust (Verschueren, 1983). In unleaded gasoline with ethanol replacing methyl tert-butyl ether, hexane concentrations in headspace vapor were 4.31 wt% for regular grade, 3.74–4.8 wt% for midgrade, and 2.3 wt% for premium grade (Harley et al., 2000). Tailpipe emission rates from gasoline vehicles were 1.82 mg/km with catalytic converters and 268 mg/km without (Schauer et al., 2002).

Purification Methods

n-Hexane can be purified by washing with chlorosulfonic acid or 35% fuming sulfuric acid instead of concentrated H?SO?, followed by drying and distillation over sodium hydride. Unsaturated impurities are removed by shaking with nitrating acid (e.g., 58% H?SO? + 25% HNO?), then washing the hydrocarbon layer with concentrated H?SO? and water, drying, and distilling over sodium or n-butyl lithium. Alternative methods include distillation under nitrogen from sodium benzophenone ketyl in tetraglyme, or passage through a silica gel column prior to distillation. As a flammable liquid and potential neurotoxin, rapid purification involves discarding the initial distillate and storing over 4A molecular sieves.