1,3-Cyclohexadiene
 | |||
| |||
| Names | |||
|---|---|---|---|
| IUPAC name
Cyclohexa-1,3-diene | |||
| Other names
1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD | |||
| Identifiers | |||
3D model (JSmol) |
|||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.008.878 | ||
PubChem CID |
|||
| RTECS number | GU4702350 | ||
| |||
| |||
| 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 | |||
EU classification (DSD) (outdated) |
Flammable (F) | ||
| R-phrases (outdated) | R11 | ||
| S-phrases (outdated) | S9 S16 S29 S33 | ||
| 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). | |||
  | |||
| Infobox references | |||
1,3-Cyclohexadiene is an organic compound with the formula (CH2)2(CH)4. It is a colorless, flammable liquid. Its refractive index is 1.475 (20 °C, D). A naturally occurring derivative of 1,3-cyclohexadiene 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
1,3-Cyclohexadiene can also be prepared by the electrocyclic reaction from 1,3,5-hexatriene either photochemically or at temperatures above 110 °C.[2]
Reactions
Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.[3]
Conversion of 1,3-cyclohexadiene to benzene + hydrogen is exothermic by about 25 kJ/mol (gas phase).[4][5]
- cyclohexane → 1,3-cyclohexadiene + 2 H2 ΔH +231.5 kJ/mol (endothermic)
- cyclohexane → benzene + + 3 H2 ΔH +205 kJ (endothermic)
- 1,3-cyclohexadiene → benzene + H2 ΔH -26.5 kJ (exothermic)
Compared with its isomer 1,4-cyclohexadiene, 1,3-cyclohexadiene is about 8.5 kJ/mol more stable.[6]
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]+.[7] Cyclohexadienes react with ruthenium trichloride to give (benzene)ruthenium dichloride dimer.
See also
References
- ↑ John P. Schaefer and Leland Endres (1967). "1,3-Cyclohexadiene". Organic Syntheses. 47: 31. ; Collective Volume, 5, p. 285
- ↑ Roberts, Stanley (1995). Comprehensive Organic Functional Group Transformations: Synthesis: Carbon with No Attached Heteroatoms. Cambridge, UK: Elsevier Science Ltd. p. 419. ISBN 0080423221.
- ↑ 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
- ↑ US National Institute of Standards and Technology, NIST Chemistry WebBook 1,3-Cyclohexadiene Benzene
- ↑ 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
- ↑ NIST Chemistry WebBook 1,4-Cyclohexadiene
- ↑ Pearson, Anthony J.; Sun, Huikai (2008). "Cyclohexadieneiron Tricarbonyl". e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00791.