Cyclohexa-1,3-diene
Names
Preferred IUPAC name
Cyclohexa-1,3-diene
Other names
1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD, Benzane
Identifiers
3D model (JSmol)
506024
ChEBI
ChemSpider
ECHA InfoCard 100.008.878
EC Number
  • 209-764-1
1657
RTECS number
  • GU4702350
UNII
UN number 1993
  • InChI=1S/C6H8/c1-2-4-6-5-3-1/h1-4H,5-6H2 checkY
    Key: MGNZXYYWBUKAII-UHFFFAOYSA-N checkY
  • InChI=1/C6H8/c1-2-4-6-5-3-1/h1-4H,5-6H2
    Key: MGNZXYYWBUKAII-UHFFFAOYAH
  • C\1=C\C=C/CC/1
Properties
C6H8
Molar mass 80.13 g/mol
Appearance Colorless liquid
Density 0.841 g/cm3
Melting point −98 °C (−144 °F; 175 K)
Boiling point 80 °C (176 °F; 353 K)
-48.6·10−6 cm3/mol
Hazards
GHS labelling:
GHS02: FlammableGHS07: Exclamation mark
Danger
H225, H335
P210, P233, P240, P241, P242, P243, P261, P271, P280, P303+P361+P353, P304+P340, P312, P370+P378, P403+P233, P403+P235, P405, P501
Flash point 26 °C (79 °F; 299 K) c.c.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cyclohexa-1,3-diene (also known as Benzane) is an organic compound with the formula (C2H4)(CH)4. It is a colorless, flammable liquid. Its refractive index is 1.475 (20 °C, D). A naturally occurring derivative of cyclohexa-1,3-diene is terpinene, a component of pine oil.

Synthesis

Cyclohexadiene is prepared by the dehydrobromination of 1,2-dibromocyclohexane:[1]

(CH2)4(CHBr)2 + 2 NaH → (CH2)2(CH)4 + 2 NaBr + 2 H2

Reactions

Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.[2]

Conversion of cyclohexa-1,3-diene to benzene + hydrogen is exothermic by about 25 kJ/mol in the gas phase.[3][4]

cyclohexane → cyclohexa-1,3-diene + 2 H2 (ΔH = +231.5 kJ/mol; endothermic)
cyclohexane → benzene + 3 H2 (ΔH = +205 kJ/mol; endothermic)
cyclohexa-1,3-diene → benzene + H2 (ΔH = -26.5 kJ/mol; exothermic)

Compared with its isomer cyclohexa-1,4-diene, cyclohexa-1,3-diene is about 1.6 kJ/mol more stable.[5]

Cyclohexadiene and its derivatives form metal-alkene complexes. Illustrative is [(C6H8)Fe(CO)3], an orange liquid. This complex reacts with hydride-abstracting reagents to give the cyclohexadienyl derivative [(C6H7)Fe(CO)3]+.[6] Cyclohexadienes react with ruthenium trichloride to give (Benzene)ruthenium dichloride dimer.[7]

See also

References

  1. ↑ Schaefer, John P.; Endres, Leland (1967). "1,3-Cyclohexadiene". Organic Syntheses. 47: 31. doi:10.15227/orgsyn.047.0031.
  2. ↑ Sanjeeva Rao Guppi, George A. O'Doherty, "1,3-Cyclohexadiene" Encyclopedia of Reagents for Organic Synthesis, 2008 John Wiley & Sons. doi:10.1002/047084289X.rn00921
  3. ↑ US National Institute of Standards and Technology, NIST Chemistry WebBook 1,3-Cyclohexadiene Benzene
  4. ↑ J. Sherman The heats of hydrogenation of unsaturated hydrocarbons Archived 2011-07-14 at the Wayback Machine Journal of the American Oil Chemists' Society; Volume 16, Number 2 / February, 1939
  5. ↑ NIST Chemistry WebBook 1,4-Cyclohexadiene
  6. ↑ Pearson, Anthony J.; Sun, Huikai (2008). "Cyclohexadieneiron Tricarbonyl". E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00791. ISBN 978-0471936237.
  7. ↑ Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. (1982). "16. (η6 -Hexamethylbenzene)Ruthenium Complexes". (η6-Hexamethylbenzene)ruthenium Complexes. Inorganic Syntheses. Vol. 21. pp. 74–78. doi:10.1002/9780470132524.ch16. ISBN 9780470132524.
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