Product Code Database
Hexane () or n-hexane is an organic compound, a straight-chain alkane with six carbon atoms and the molecular formula 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, and modern gasoline blends contain about 3% hexane.
The term hexanes refers to a mixture, 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 (e.g., as cleaning solvent or for chromatography).
| Normal hexane, n-Hexane | Hexane | CH3(CH2)4CH3 | |
| Isohexane | 2-Methylpentane | (CH3)2CH(CH2)2CH3 | |
| 3-Methylpentane | CH3CH2CH(CH3)CH2CH3 | ||
| 2,3-Dimethylbutane | (CH3)2CHCH(CH3)2 | ||
| Neohexane | 2,2-Dimethylbutane | (CH3)3CCH2CH3 |
A typical laboratory use of hexanes is to extract petroleum and grease contaminants from water and soil for analysis. Since hexane cannot be easily deprotonation, 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 chromatography 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 fuel, n-hexane has low research and motor Octane rating 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%.
Hexane has considerable vapor pressure at room temperature:
The US National Institute for Occupational Safety and Health (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 (PEL) by the Occupational Safety and Health Administration 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) present an aspiration risk. n-Hexane 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 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 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.
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