hexane is an organic compound , a straight chain alkane with six carbon atoms and has the molecular formula C 6 H 14 .
Hexane is an important component of gasoline. It is a colorless liquid, odorless when pure, and with a boiling point of about 69 °C (156 °F). It is widely used as a cheap, relatively safe, largely unreactive and easily evaporated non-polar solvent.
The term hexanes refers to a mixture, of hexanes, composed largely (>60%) of the isomeric compounds with amounts of 2-methylpentane and 3-methylpentane, and possibly smaller amounts of the nonisomeric C 5 , C 6 , and C 7 (cyclo)alkanes. Hexanes is cheaper than hexanes and is often used in large-scale operations that do not require an isomer (for example, for cleaning solvent or chromatography).
| Property | |
|---|---|
| chemical formula | C6 H14 _ _ |
| molar mass | ८६.१७८ g·mol −1 |
| appearance | colorless liquid |
| dirt | of petrol |
| density | 0.6606 g ml −1 |
| Melting point | -96 to -94 ° C; −141 to −137 °F; 177 to 179 |
| boiling point | 68.5 to 69.1 °C; 155.2 to 156.3 degrees Fahrenheit; 341.6 to 342.2 K |
| Solubility in water | 9.5 mg L -1 |
| log p | 3.764 |
| vapor pressure | 17.60 kPa (at 20.0 °C) |
| Henry’s law constant ( kH ) | 7.6 nmol Pa -1 kg -1 |
| UV-Vis (λmax ) | 200 nm |
| Magnetic Sensitivity (χ) | −74.6 10 −6 cm 3 /mol |
| Refractive Index ( ND ) | 1.375 |
| viscosity | 0.3 MPa s |
| Dipole rotation | 0.08 d |
isomers
Use
In industry, hexane is used in the manufacture of glue for shoes, leather products and roofing. They are also used to extract cooking oil (such as canola oil or soy oil) from the seeds, to clean and degrease a variety of items, and in textile manufacturing. They are commonly used in edible-based soybean oil extraction in the United States, and are potentially present as contaminants in all soy food products in which the technology is used; The lack of FDA regulation of this contaminant is the subject of some controversy. [7] [8]
A typical laboratory use of hexane is to remove oil and grease contaminants from water and soil for analysis. [9] Since hexane cannot be easily precipitated, it is used in the laboratory for reactions that involve very strong bases, such as the preparation of organolithium. For example, butyllithium is commonly supplied as a hexane solution.
Hexane is commonly used as a non-polar solvent in chromatography. Higher alkanes present as impurities in hexane have the same retention time as the solvent, which means that even fractions containing hexanes will have these impurities. In preliminary chromatography, the concentration of a large amount of hexanes may result in a sample that is significantly contaminated by alkanes. This can result in a solid compound in the form of oil and alkanes can interfere with the analysis. [ citation needed ]
Production
Hexane is mainly obtained by refining crude oil. The exact composition of the fraction depends largely on the source of the oil (raw or refined) and the constraints of refining. The industrial product (usually about 50% by weight of the straight-chain isomer) has a boiling fraction at 65–70 °C (149–158 °F).
preparation
Although hexane is useful to laboratories as an extraction solvent, they are usually difficult to purchase outside of a professional laboratory. However, hexane can be isolated from many sources, including gasoline, camping fuel, and many hydrocarbon-based solvents. The typical process to isolate hexane from these involves fractional distillation of the hydrocarbon source, with the fraction collected at approximately 65–70 °C (149–158 °F). [10] This is followed by oxidation of the side products under acidic environments such as alcohols, alkanes, and toluene, and re-distillation of the solution to separate the mixture of n-hexane and various isomers. [11] The final product typically comprises about 50 percent of the volume of the straight chain isomer.
physical properties
All alkanes are colourless. [12] [13] The boiling points of various hexane are somewhat similar and, as with other alkanes, are usually lower for the more branched forms. Melting points vary greatly and the trend is not clear.
| isomer | MP (°C) | MP (degrees Fahrenheit) | BP (°C) | BP (degrees Fahrenheit) |
|---|---|---|---|---|
| n -hexane | -95.3 | −139.5 | 68.7 | 155.7 |
| 3-methylpentane | -118.0 | −180.4 | 63.3 | १४५.९ |
| 2-methylpentane (isohexane) | −153.7 | −244.7 | 60.3 | १४०.५ |
| 2,3-dimethylbutane | −128.6 | −199.5 | 58.0 | १३६.४ |
| 2,2-dimethylbutane (neohexane) | -99.8 | −147.6 | 49.7 | 121.5 |
Hexane at room temperature has a considerable vapor pressure:
| Temperature (°C) | Temperature (degrees Fahrenheit) | Vapor pressure (mmHg) | Vapor pressure (kPa) |
|---|---|---|---|
| -40 | -40 | 3.36 | 0.448 |
| -30 | -22 | 7.12 | 0.949 |
| -20 | -4 | 14.01 | १.८६८ |
| -10 | 14 | 25.91 | ३.४५४ |
| 0 | 32 | 45.37 | 6.049 |
| 10 | 50 | 75.74 | 10.098 |
| 20 | ६८ | १२१.२६ | १६.१६७ |
| 25 | 77 | १५१.२८ | 20.169 |
| 30 | ८६ | १८७.११ | २४.९४६ |
| 40 | १०४ | 279.42 | ३७.२५३ |
| 50 | 122 | 405.31 | 54.037 |
| 60 | 140 | ५७२.७६ | 76.362 |
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Like most alkanes, hexane exhibits particularly low reactivity and are suitable solvents for reactive compounds. Commercial samples of n-hexane however often contain methylcyclopentane, which contains tertiary C-H bonds, which are incompatible with some radical reactions. [15]
Security
Inhalation of n -hexane at 5000 ppm for 10 min produces marked dizziness; 2500-1000 ppm for 12 hours produces drowsiness, fatigue, loss of appetite, and paresthesias in the distal extremities; 2500-5000 ppm produces muscle weakness, chills in the extremities, blurred vision, headache and anorexia. [16] Long-term occupational exposure to elevated levels of n-hexane has been shown to be associated with peripheral neuropathy in auto mechanics in the Americas, and associated with neurotoxicity in workers in printing presses, and shoe and furniture factories in Asia, Europe and North America. Has happened. , [17]
The US National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) for hexane isomers (not n-hexane) at 100 ppm (350 mg/m3 (0.15 g/cu ft) ) . – Hourly workdays. [18] However, for n-hexane, the current NIOSH REL is 50 ppm (180 mg/m3 (0.079 gr/cu ft)) in an 8-hour workday . [19] This limit was proposed by the Occupational Safety and Health Administration as a permissible exposure limit (PEL) in 1989; However, in 1992 this PEL was dismissed in US courts. [20] The current n-hexane PEL in the US is 500 ppm (1,800 mg/ m3(0.79 gr/cu ft)). [19]
Hexane and other volatile hydrocarbons (petroleum ethers) present an aspiration risk. [21] n -Hexane is sometimes used as a denaturant for alcohol, and as a cleaning agent in the textile, furniture, and leather industries. It is gradually being replaced by other solvents. [22]
Like gasoline, hexane is highly volatile and poses an explosion risk. The ignition of illegally discharged hexane vapors into the sewers of Louisville (Kentucky) from a soybean processing plant owned by Ralston-Purina caused a series of explosions that destroyed more than 21 km of sewer lines and roads in that city. done.
Events
Occupational hexane poisoning has occurred to Japanese sandal workers, Italian shoe workers, [23] Taiwanese press proofing workers, and others. [24] Analysis of Taiwanese workers has shown occupational exposure to substances including n -hexane. [25] In 2010–2011, Chinese workers making iPhones suffered hexane poisoning. [26] [27]
Hexane was identified as the cause of the Louisville sewer explosions on February 13, 1981, which destroyed more than 13 miles (21 km) of sewer lines and roads in the center of Louisville in Kentucky, United States.
biological change
n -hexane is biotransformed in the body to 2-hexanol and further into 2,5-hexanediol. The conversion is catalyzed by the enzyme cytochrome P450 using oxygen from the air. 2,5-hexanediol can be further oxidized to 2,5-hexanedione, which is neurotoxic and produces a polyneuropathy. [22] Considering this behavior, the replacement of n -hexane as a solvent is discussed. n-heptane is a possible alternative.
