Cyclohexa-1,3-diene
Chemical compound
From Wikipedia, the free encyclopedia
Cyclohexa-1,3-diene 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). It is one of two isomers of cyclohexadiene, the other being 1,4-cyclohexadiene. It is commonly referred to as "benzane" due to the structural similarities to benzene and benzyne.
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| Names | |||
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| Preferred IUPAC name
Cyclohexa-1,3-diene | |||
| Other names
1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD, Benzane | |||
| Identifiers | |||
3D model (JSmol) |
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| 506024 | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.008.878 | ||
| EC Number |
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| 1657 | |||
PubChem CID |
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| RTECS number |
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| UNII | |||
| UN number | 1993 | ||
CompTox Dashboard (EPA) |
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| Properties | |||
| C6H8 | |||
| Molar mass | 80.13 g/mol | ||
| Appearance | Colorless liquid | ||
| Density | 0.841 g/cm3 | ||
| Melting point | â98 °C (â144 °F; 175 K) | ||
| Boiling point | 80 °C (176 °F; 353 K) | ||
| â48.6·10â6 cm3/mol | |||
| Hazards | |||
| GHS labelling: | |||
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| 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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Synthesis
Cyclohexadiene is prepared by the double dehydrobromination of 1,2-dibromocyclohexane:[1]
- (CH2)4(CHBr)2 + 2 NaH â (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 â cyclohexa-1,3-diene + 2 H2 (ÎH = +231.5 kJ/mol; endothermic)
- cyclohexane â benzene + 3 H2 (ÎH = +205 kJ/mol; endothermic)
- cyclohexa-1,3-diene â benzene + H2 (ÎH = -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 (diene)iron tricarbonyl 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]
Occurrence
Cyclohexa-1,3-diene itself is rare in nature, but the cyclohexa-1,3-diene motif is fairly common.[8] One example is chorismic acid, an intermediate in the shikimic acid pathway. Of the several examples of the terpenoids and terpenes, a prominent example is phellandrene. An unusual derivative is cis-1,2-dihydrocatechol.
Coenzyme A-conjugated to the 2-position of cyclohexadiene-2-carboxylic acid is an intermediate in the biodegradation of aromatic carboxylic acids.[9]