Hexane () or ''n''-hexane is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

, a straight-chain

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...

with six

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

atoms and the

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

C₆H₁₄. Hexane is a colorless liquid, odorless when pure, and with a boiling point of approximately . It is widely used as a cheap, relatively safe, largely unreactive, and easily evaporated

non-polar solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

, and modern

gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...

blends contain about 3% hexane. The term hexanes refers to a

mixture In chemistry, a mixture is a material made up of two or more different chemical substances which can be separated by physical method. It is an impure substance made up of 2 or more elements or compounds mechanically mixed together in any proporti ...

, composed largely (>60%) of ''n''-hexane, with varying amounts of the isomeric compounds 2-methylpentane and 3-methylpentane, and possibly, smaller amounts of nonisomeric C₅, C₆, and C₇ (cyclo)alkanes. These "hexanes" mixtures are cheaper than pure hexane and are often used in large-scale operations not requiring a single

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

(e.g., as cleaning solvent or for

chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...

Isomers

Uses

In industry, hexanes are used in the formulation of

glue Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...

s for shoes,

leather Leather is a strong, flexible and durable material obtained from the tanning (leather), tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffal ...

products, and roofing. They are also used to extract

cooking oil Cooking oil (also known as edible oil) is a plant or animal liquid fat used in frying, baking, and other types of cooking. Oil allows higher cooking temperatures than water, making cooking faster and more flavorful, while likewise distributing h ...

s (such as canola oil or

soybean oil Soybean oil (British English: soyabean oil) is a vegetable oil extracted from soybean (''Glycine max'') legumes. It is one of the most widely consumed cooking oils and the second most consumed vegetable oil. As a drying oil, processed soybean 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. Hexanes are commonly used in

as a non-polar solvent. Higher alkanes present as impurities in hexanes have similar retention times as the solvent, meaning that fractions containing hexane will also contain these impurities. In preparative chromatography, concentration of a large volume of hexanes can result in a sample that is appreciably contaminated by alkanes. This may result in a solid compound being obtained as an oil and the alkanes may interfere with analysis. As an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

fuel, n-hexane has low research and motor octane numbers of 25 and 26 respectively. In 1983 its share in Japanese gasoline varied around 6%, in 1992 it was present in American gas between 1 and 3%, and in Swedish automobile fuel in the same year the share was consistently under 2%, often below 1%. By 2011 its share in US gas stood between 1 and 7%.

Production

Hexane is chiefly obtained by

refining Refining is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum w ...

crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...

. 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 .

Physical properties

All alkanes are colorless. 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. Hexane has considerable

vapor pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

at room temperature:

Reactivity

Like most alkanes, hexanes characteristically exhibit low reactivity and are suitable solvents for reactive compounds. Commercial samples of ''n''-hexane however often contains methylcyclopentane, which features tertiary C-H bonds, which are incompatible with some radical reactions.

Safety

Inhalation of ''n''-hexane at 5000 ppm for 10 minutes produces marked vertigo; 2500-1000 ppm for 12 hours produces

drowsiness Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

, loss of appetite, and

paresthesia Paresthesia is a sensation of the skin that may feel like numbness (''hypoesthesia''), tingling, pricking, chilling, or burning. It can be temporary or Chronic condition, chronic and has many possible underlying causes. Paresthesia is usually p ...

in the distal extremities; 2500–5000 ppm produces muscle weakness, cold pulsation in the extremities, blurred vision,

headache A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of Depression (mood), depression in those with severe ...

, and

anorexia Anorexia nervosa (AN), often referred to simply as anorexia, is an eating disorder characterized by Calorie restriction, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. Individuals wit ...

. Chronic occupational exposure to elevated levels of ''n''-hexane has been demonstrated to be associated with

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

in auto mechanics in the US, and

neurotoxicity Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...

in workers in printing presses, and shoe and furniture factories in Asia, Europe, and North America. The US

National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the List of United States federal agencies, United States federal agency responsible for conducting research and making recommendations for the prevention of work-related occ ...

(NIOSH) has set a recommended exposure limit (REL) for hexane isomers (not ''n''-hexane) of 100 ppm () over an 8-hour workday. However, for ''n''-hexane, the current NIOSH REL is 50 ppm () over an 8-hour workday. This limit was proposed as a

permissible exposure limit The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agents such as high level noise. Permissible exposure limits were established by the Occupational ...

(PEL) by the

Occupational Safety and Health Administration The Occupational Safety and Health Administration (OSHA; ) is a regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. The United States Congress established ...

in 1989; however, this PEL was overruled in US courts in 1992. The current n-hexane PEL in the US is 500 ppm (). Hexane and other volatile hydrocarbons (

petroleum ether Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35–60 °C, and commonly used as a laboratory solvent. Despite the name, petroleum ether is not an ether; the term is used only figurativ ...

) present an aspiration risk. ''n''-Hexane is sometimes used as a denaturant for alcohol, and as a cleaning agent in the

textile Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, and different types of #Fabric, fabric. ...

furniture Furniture refers to objects intended to support various human activities such as seating (e.g., Stool (seat), stools, chairs, and sofas), eating (table (furniture), tables), storing items, working, and sleeping (e.g., beds and hammocks). Furnitur ...

, and leather industries. It is slowly being replaced with other solvents. Like gasoline, hexane is highly volatile and is an explosion risk. The 1981 Louisville sewer explosions, which destroyed over of sewer lines and streets in Kentucky, were caused by ignition of hexane vapors which had been illegally discharged from a

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...

processing plant owned by Ralston-Purina. Hexane was attributed as the cause of an explosion that occurred in the National University of Río Cuarto, Argentina on 5 December 2007, due to a hexane spill near a heat-producing machine that exploded, producing a fire that killed one student and injured 24 more.

Incidents

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. In 2010–2011, Chinese workers manufacturing iPhones were reported to have suffered hexane poisoning.

Biotransformation

''n''-Hexane is biotransformed to 2-hexanol and further to 2,5-hexanediol in the body. The conversion is catalyzed by the enzyme

cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...

utilizing oxygen from air. 2,5-Hexanediol may be further oxidized to 2,5-hexanedione, which is

neurotoxic Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...

and produces a

polyneuropathy Polyneuropathy () is damage or disease affecting peripheral nerves (peripheral neuropathy) in roughly the same areas on both sides of the body, featuring weakness, numbness, and burning pain. It usually begins in the hands and feet and may prog ...

. In view of this behavior, replacement of ''n''-hexane as a solvent has been discussed. ''n''-Heptane is a possible alternative.

References

External links

International Chemical Safety Card 1262
(2-methylpentane)

Phytochemica l database entry

*Australian ttps://web.archive.org/web/20090912082512/http://www.npi.gov.au/database/substance-info/profiles/47.html National Pollutant Inventory (NPI)page
"EPA does not consider n-hexane classifiable as a human carcinogen."
Federal Register / Vol. 66, No. 71 / Thursday, 12 April 2001 / Rules and Regulations {{authority control Alkanes Hydrocarbon solvents Commodity chemicals