Hexane Hexane /ˈhɛkseɪn/ is an alkane of six carbon
atoms, with the chemical formula C6H14. The term may refer to any of the five structural
isomers with that formula, or to a mixture of them. In IUPAC nomenclature, however, hexane
is the unbranched isomer (n-hexane); the other four structures are named as methylated derivatives
of pentane and butane. IUPAC also uses the term as the root of many compounds with a
linear six-carbon backbone, such as 2-methylhexane (C7H16), which is also called "isoheptane".
Hexanes are significant constituents of gasoline. They are all colorless liquids at room temperature,
odorless when pure, with boiling points between 50 and 70 °C. They are widely used as cheap,
relatively safe, largely unreactive, and easily evaporated non-polar solvents.
Uses In industry, hexanes are used in the formulation
of glues for shoes, leather products, and roofing. They are also used to extract cooking
oils (such as canola oil) from seeds, for cleansing and degreasing a variety of items,
and in textile manufacturing. A typical laboratory use of hexanes is to
extract oil and grease contaminants from water and soil for analysis. Since hexane cannot
be easily deprotonated, it is used in the laboratory for reactions that involve very
strong bases, such as the preparation of organolithiums. For example, butyllithiums are typically supplied
as a hexane solution. In many applications (especially pharmaceutical),
the use of n-hexane is being phased out due to its long term toxicity. It is often replaced
by n-heptane, which will not form the toxic metabolite hexane-2,5-dione.
Production Hexanes are chiefly obtained by the refining
of crude oil. The exact composition of the fraction depends largely on the source of
the oil (crude or reformed) and the constraints of the refining. The industrial product (usually
around 50% by weight of the straight-chain isomer) is the fraction boiling at 65–70 °C.
Physical properties All alkanes are colourless. The boiling points
of the various hexanes are somewhat similar and, as for other alkanes, are generally lower
for the more branched forms. The melting points are quite different and the trend is not apparent.
Normal hexane (n-hexane) has considerable vapor pressure at room temperature:
Safety Acute exposure to n-hexane usually occurs
by inhalation, but it may be absorbed orally and transdermally. Minor exposures may occur
when persons fill their automobile fuel tanks with gasoline. Recent research suggests that
certain fungi may be able to produce n-hexane. The acute toxicity of n-hexane is rather low.
However, it has been reported to be the most highly toxic member of the alkanes. When n-hexane
is ingested, it causes nausea, vertigo, bronchial irritation, intestinal irritation and CNS
effects. It has been reported that ~ 50 g of n-hexane may be fatal to humans. Furthermore,
n-hexane is biotransformed to 2-hexanol and further to 2,5-hexanediol by cytochrome P450
mixed function oxidases by omega oxidation. 2,5-Hexanediol may be further oxidized to
2,5-hexanedione, which is neurotoxic and produces a polyneuropathy.
n-Hexane is also used as a solvent in the extraction of oil from seeds (soybean, cottonseed,
flaxseed, safflower seed, and others). It is sometimes used as a denaturant for alcohol,
and as a cleaning agent in the textile, furniture, and leather industries. It is slowly being
replaced with other less toxic solvents. The National Institute for Occupational Safety
and Health recommended exposure limit is 50 ppm (180 mg m−3), expressed as an 8 h time-weighted
average (TWA). A peer reviewed study found that inhalation of n-Hexane at 5000 ppm for
10 minutes produces marked vertigo; 2500-1000 ppm for 12 hours produces drowsiness, fatigue,
loss of appetite, paresthesia in distal extremities; 2500-500 ppm produces muscle weakness, cold
pulsation in extremities, blurred vision, headache and anorexia.
Occupational hexane poisoning has occurred with Japanese sandal workers, Italian shoe
workers, Taiwan press proofing workers, and others. Analysis of Taiwanese workers has
shown occupational exposure to substances including n-Hexane. Recently, Chinese workers
manufacturing iPhones have suffered hexane poisoning.