Hexanes

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In chemistry, hexanes are a group of aliphatic, saturated hydrocarbons or alkanes that contain all six carbon atoms in the molecule. The molecular formula of the compounds is C 6 H 14 . There are five constitutional isomers :

  1. n -hexane
  2. 2-methylpentane
  3. 3-methylpentane
  4. 2,2-dimethylbutane
  5. 2,3-dimethylbutane

In addition to the n -hexane, two methylpentanes and two dimethylbutanes can be formulated.

properties

All compounds are volatile liquids with relatively similar properties. The branching of the carbon chain results in a sometimes significant drop in the melting points. The boiling points decrease less sharply. The vapor pressure values ​​behave accordingly at lower temperatures. The given data on the inflammation behavior should be viewed critically. Some of the flash point information corresponds to the measurement limits of flash point apparatus. There is actually no measuring device for a flash point of −48 ° C. The same explosion limit data for the branched hexanes is astonishing, since the formation of ignitable atmospheres correlates with the vapor pressure function and these differ for the individual isomers. With regard to the self-ignition behavior, a clear dependence on the degree of branching of the carbon chain can be read off from the ignition temperatures. The ignition temperatures of methylpentanes increase by 70 K compared to n -hexane, those of dimethylbutanes by a further 100 K.

Comparison of physical properties of hexanes
Surname n -hexane 2-methylpentane 3-methylpentane 2,2-dimethylbutane 2,3-dimethylbutane
other names Hexane ( IUPAC ) Isohexane Neohexane Diisopropyl
Structural formula Hexane skeleton.svg 2-methylpentane.svg 3-methylpentane.svg 2,2-dimethylbutane.svg 2,3-dimethylbutane 200.svg
CAS number 110-54-3 107-83-5 96-14-0 75-83-2 79-29-8
PubChem 8058 7892 7282 6403 6589
Molecular formula C 6 H 14
Molar mass 86.18 g mol −1
Brief description colorless liquid
Melting point −95 ° C −154 ° C −118 ° C −100 ° C −129 ° C
boiling point 69 ° C 60 ° C 63 ° C 50 ° C 58 ° C
Vapor pressure (20 ° C) 162 mbar 227 mbar 203 mbar 348 mbar 255 mbar
Vapor pressure (30 ° C) 249 mbar 344 mbar 309 mbar 511 mbar 381 mbar
Vapor pressure (50 ° C) 540 mbar 719 mbar 651 mbar 1020 mbar 782 mbar
density 0.66 g cm −3 0.65 g cm −3 0.66 g cm −3 0.65 g cm −3 0.66 g cm −3
Solubility in water 10 mg l −1 14 mg l −1 18 mg l −1 24 mg l −1
Flash point <−20 ° C <−7 ° C <−20 ° C −48 ° C −29 ° C
Lower explosion limit (LEL) 1.0% by volume 1.2% by volume 1.2% by volume 1.2% by volume 1.2% by volume
35 g m −3 40 g m −3 40 g m −3 40 g m −3 40 g m −3
Upper explosion limit (UEL) 8.9% by volume 7.0% by volume 7.0% by volume 7.0% by volume 7.0% by volume
319 g m −3 250 g m −3 250 g m −3 250 g m −3 250 g m −3
Ignition temperature 230 ° C 300 ° C 300 ° C 435 ° C 415 ° C

Individual evidence

  1. ↑ All data was taken from the GESTIS database, the individual links are in the name line.
  2. ↑ Entry for CAS no. 110-54-3 in the GESTIS substance database of the IFA , accessed on July 25, 2019(JavaScript required) .
  3. ↑ Entry for CAS no. 107-83-5 in the GESTIS substance database of the IFA , accessed on April 11, 2018(JavaScript required) .
  4. ↑ Entry for CAS no. 96-14-0 in the GESTIS substance database of the IFA , accessed on April 11, 2018(JavaScript required) .
  5. ↑ Entry for CAS no. 75-83-2 in the GESTIS substance database of the IFA , accessed on April 11, 2018(JavaScript required) .
  6. ↑ Entry for CAS no. 79-29-8 in the GESTIS substance database of the IFA , accessed on July 25, 2019(JavaScript required) .