Pentane

Pentane

Distilled lab-grade pentane.
Names
IUPAC name Pentane
Preferred IUPAC name n-Pentane
Systematic IUPAC name n-Pentane
Other names Amyl hydride Pentan Skellysolve A
Identifiers
Jmol-3D images	Image
SMILES CCCCC
Properties
Chemical formula	C5H12
Molar mass	72.15 g/mol
Appearance	Colorless volatile liquid
Odor	Lighter-fluid like
Density	0.626 g/cm3
Melting point	−129.8 °C (−201.6 °F; 143.3 K) (decomposes)
Boiling point	36 °C (97 °F; 309 K)
Solubility in water	0.04 g/L (at 20 °C)
Solubility	Miscible with chloroform, ethanol, hydrocarbons
Vapor pressure	57.90 kPa (at 20.0 °C)
Acidity (pKa)	~45
Viscosity	0.240 cP (at 20 °C)
Thermochemistry
Std molar entropy (So298)	263.47 J·K−1·mol−1
Std enthalpy of formation (ΔfHo298)	−174.1–−172.9 kJ/mol
Hazards
Safety data sheet	BOC
Flash point	−49 °C (-56.2 °F; 224 K)
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	3,000 mg/kg (dermal, rabbit) 5,000 mg/kg (oral, mouse)
LC50 (Median concentration)	130,000 mg/m3 (mouse, 30 min) 128,200 ppm (mouse, 37 min) 325,000 mg/m3 (mouse, 2 hr)
Related compounds
Related compounds	Butane Hexane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Pentane is an organic compound, an alkane with 5 carbon atoms, with the chemical formula C₅H₁₂. It is composed of three isomers, n-pentane, isopentane (or methylbutane) and neopentane. While the term "pentane" may refer to any of the isomers, the IUPAC nomenclature specifies that the term must only be used for the n isomer.

Properties

Chemical

Pentane, like other hydrocarbons, will burn in air when ignited by an open flame to release carbon dioxide and water vapor.

C₅H₁₂ + 8 O₂ → 5 CO₂ + 6 H₂O

Like other alkanes, pentane undergo free radical chlorination:

C₅H₁₂ + Cl₂ → C₅H₁₁Cl + HCl

Such reactions are unselective; with n-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur.

Physical

Pentane is a colorless liquid hydrocarbon, with a characteristic smell. It is insoluble in water, but miscible with other organic solvents. Pentane has a density of 0.621 g/cm³, meaning it's lighter than water. It boils at 36 °C and melts at -130 °C.

Its isomer neopentane, though, is a gas that boils at 9.5 °C, is the heaviest and the most high-boiling of all hydrocarbon gases.

Availability

Pentane can be purchased form chemical suppliers. Certain pesticides contain pentane.

Some car starter fluids contain pentane to increase the volatility of the fluid. You will need very a long fractional distillation column or repeated distillations to separate it from the mixture, as the boiling point of diethyl ether (34.6 °C), the other useful compound from starter fluid, is very close to that of pentane (36.3 °C). Additionally, you can add conc. sulfuric acid to separate the pentane from the ether (diethyl ether is soluble in conc. sulfuric acid, pentane is insoluble), then use a separatory funnel to remove the ether-acid and pentane layers. The ether can be recovered from the solution via distillation. This route however, is not very cost effective.

At least one type of charcoal lighter fluids can contain up to 25% n-pentane. Fractional distillation is required to extract the compound from the mixture.

Preparation

Pentane can be prepared by decarboxylating the salts of caproic acid, found in various oily plants, with a strong base. Be careful, as the reaction may foam up.

Projects

• Extraction (solvent)
• Phthalic and maleic anhydride synthesis
• Purification of organometallic compounds
• Liquid chromatography

Handling

Safety

Pentane, due to its low boiling point, evaporates very fast and the vapors are hazardous if inhaled, work should be performed in a fumehood or outside, never in a closed chamber without ventilation. If pentane is inhaled in large amounts, further exposure should be limited and one should seek fresh air.

Pentane is highly flammable and should be kept away from open flames.

Storage

Due to its low boiling point, pentane should be stored in closed glass bottles, at constant temperature, away from any source of heat, even small ones. If it's stored at low temperatures, and then brought at room temperatures or slightly higher, pressure will build up in the bottle from the vapors and the bottle can explode. It is mandatory to open the bottle from time to time, to release the pressure.

Commercial pentane contains small amounts of inhibitors, that prevent its degradation, over long periods of time. They can be removed by distillation, as their boiling point is much higher than that of pentane.

Disposal

Pentane can be safely burned, as it theoretically should not generate any toxic byproducts. However, like other hydrocarbons, carbon monoxide can be formed so this should not be performed indoors.

References

Relevant Sciencemadness threads

• Hexane or Pentane?