|Molecular formula||C 6 H 14|
colorless liquid with a weak gasoline smell
|External identifiers / databases|
|Molar mass||86.18 g mol −1|
0.66 g cm −3
−95 ° C
69 ° C
162 h Pa (20 ° C)
1.3727 (20 ° C)
DFG / Switzerland: 50 ml m −3 or 180 mg m −3
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Hexane is a colorless, volatile liquid that smells slightly like gasoline . The boiling point under normal pressure is 68.8 ° C. The compound melts at −95.4 ° C. The relative dielectric constant is 1.8 at 20 ° C. It is practically insoluble in water. It is readily soluble in organic solvents such as alcohols (with the exception of methanol ), ethers and benzene .
The compound forms azeotropically boiling mixtures with a number of other solvents . The azeotropic compositions and boiling points can be found in the following table. No azeotropes are formed with cyclohexane , n- pentane , heptane , octane , toluene , ethylbenzene , xylene , cyclohexanol and diethyl ether .
|Azeotropes with various solvents (according to Smallwood)|
|Content of hexane||in%||94||72||79||96||77|
|boiling point||in ° C||62||50||59||66||63|
|solvent||1-butanol||i-butanol||2-butanol||Ethylene glycol ethyl ether||Acetonitrile|
|Content of hexane||in%||97||98||92||95||72|
|boiling point||in ° C||68||68||67||66||52|
|solvent||chloroform||acetic acid||acetone||Methyl ethyl ketone||Diisopropyl ether|
|Content of hexane||in%||16||95||41||71||47|
|boiling point||in ° C||60||68||50||64||67|
|solvent||Dioxane||THF||Methyl acetate||Ethyl acetate||Isopropyl acetate|
|Content of hexane||in%||98||50||39||62||91|
|boiling point||in ° C||60||63||52||65||69|
According to Antoine, the vapor pressure function results from log 10 (P) = A− (B / (T + C)) (P in bar, T in K) with A = 3.45604, B = 1044.038 and C = −53.893 in the temperature range from 177.70 to 264.93 K or with A = 4.00266, B = 1171.530 and C = −48.784 in the temperature range from 286.18 to 342.69 K.
|Standard enthalpy of formation||Δ f H 0 liquid
Δ f H 0 gas
|−198.7 kJ mol −1
−167.1 kJ mol −1
|as a liquid
as a gas
|Standard entropy||S 0 liquid
S 0 gas
|296.06 J mol −1 K −1
388.82 J mol −1 K −1
|as a liquid
as a gas
|Enthalpy of combustion||Δ c H 0 liquid||−4163.2 kJ mol −1|
|Heat capacity||c p||194.97 J mol −1 K −1 (25 ° C)
2.30 J g −1 K −1 (25 ° C)
142.6 J mol −1 K −1 (25 ° C )
1.65 J g −1 K −1 (25 ° C)
|as a liquid
as a gas
|Critical temperature||T c||507.5 K|
|Critical pressure||p c||29.9 bar|
|Critical volume||V c||0.368 l mol −1|
|Critical density||ρ c||2.72 mol·l −1|
|Acentric factor||ω c||0.30126|
|Enthalpy of fusion||Δ f H 0||13.08 kJ mol −1||at the melting point|
|Enthalpy of evaporation||Δ V H 0
Δ V H
|31.73 kJ mol −1
28.85 kJ mol −1
at normal pressure boiling point
The temperature dependence of the enthalpy of evaporation can be calculated according to the equation Δ V H 0 = Aexp (−αT r ) (1 − T r ) β (Δ V H 0 in kJ / mol, T r = (T / T c ) reduced temperature) with Describe A = 43.85 kJ / mol, α = −0.039, β = 0.397 and T c = 507.4 K in the temperature range between 298 K and 444 K.
Vapor pressure function of hexane
n- hexane forms highly flammable vapor-air mixtures. The compound has a flash point of −20 ° C. The explosion range is between 1% by volume (35 g / m 3 ) as the lower explosion limit (LEL) and 8.9% by volume (319 g / m 3 ) as the upper explosion limit (UEL). A correlation of the explosion limits with the vapor pressure function results in a lower explosion point of −28 ° C and an upper explosion point of 7 ° C. The explosion limits are pressure dependent. A decrease in pressure leads to a reduction in the explosion area. The lower explosion limit changes only slightly up to a pressure of 100 mbar and only increases at pressures below 100 mbar. The upper explosion limit decreases analogously with falling pressure.
|Explosion limits under reduced pressure (measured at 100 ° C)|
|Lower explosion limit (LEL)||in% by volume||0.9||0.9||0.9||0.9||1.0||1.0||1.0||1.1||1.2||1.6||3.5|
|in g m −3||30th||31||32||33||34||35||37||39||43||58||125|
|Upper explosion limit (UEL)||in% by volume||8.9||8.7||8.3||7.8||7.6||7.5||7.4||7.3||7.2||6.0||4.7|
|in g m −3||319||312||297||279||272||269||265||262||258||215||168|
The lower explosion limit decreases with increasing temperature. The linear function LEL (T) = LEL (T 0 ) · [1 + k u (TT 0 )] (with T 0 = 20 ° C) results in a temperature coefficient k u of −0.0027 K −1 .
|Lower explosion limits with increasing temperature|
|temperature||in ° C||20th||100||150||200||250|
|Lower explosion limit (LEL)||in% by volume||1.0||0.9||0.6||0.5||0.4|
The limit oxygen concentration at 20 ° C is 9.1% by volume, at 100 ° C it is 8.3% by volume. The value tends to increase with decreasing pressure and decrease with increasing temperature. The maximum explosion pressure is 9.5 bar. The maximum explosion pressure decreases as the outlet pressure decreases.
|Maximum explosion pressure and limit oxygen concentration under reduced pressure|
|Maximum explosion pressure||in cash||at 20 ° C||9.6||7.4||5.6||3.7||2.8||1.8||1.4||1.1|
|Limit oxygen concentration||in vol%||at 20 ° C||9.1||9.5||10.1||10.8|
|at 100 ° C||8.3||8.3||8.8|
With a minimum ignition energy of 0.24 mJ, vapor-air mixtures are extremely ignitable. The limit gap width was determined to be 0.93 mm. This results in an assignment to explosion group IIA. The ignition temperature is 230 ° C. The substance therefore falls into temperature class T3.
Hexane is used in organic chemistry as a solvent and reaction medium in polymerizations , as a diluent for fast-drying paints, printing inks and adhesives and as an elution and solvent in thin-layer chromatography . It is still used to manufacture plastics and synthetic rubber, as well as for oil and fat extraction . Since it does not attack polystyrene , unlike many organic solvents, and is highly volatile, it is used as a solvent for styrofoam glue .
Safety instructions / toxicology
Hexane is addictive and harmful to health. Hexane is hazardous to water ( WGK 2). Hexane is metabolized in the body to 2,5-hexanedione , this leads to nerve damage and is excreted in the urine. Because of this harmful effect, n-hexane is increasingly being replaced by n-heptane
In 2012, hexane was included in the EU's ongoing action plan ( CoRAP ) in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. Hexane uptake was caused by concerns about its classification as a CMR substance, high (aggregated) tonnage, other hazard-related concerns and widespread use. The reassessment took place from 2012 and was carried out by Germany . A final report was then published.
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