Cyclooctatetraene

Structural formula
General
Surname	Cyclooctatetraene
other names	COT Cycloocta-1,3,5,7-tetraene [8] Annulene
Molecular formula	C 8 H 8
Brief description	yellow liquid with an unpleasant odor
External identifiers / databases
CAS number 629-20-9 EC number 211-080-3 ECHA InfoCard 100.010.074 PubChem 637866 Wikidata Q900926
properties
Molar mass	104.15 g mol −1
Physical state	liquid
density	0.93 g cm −3
Melting point	0 ° C
boiling point	142-143 ° C
Vapor pressure	10.5 h Pa (20 ° C)
solubility	almost insoluble in water
Refractive index	1.5381 (20 ° C)
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 225-304-315-319-335-412 P: 210-261-273-301 + 310-305 + 351 + 338-331
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

Cyclooctatetraene (COT) is an organic - chemical compound from the group of cyclic hydrocarbons . The compound with the empirical formula C ₈ H ₈ has four conjugated C = C double bonds .

In contrast to benzene (C ₆ H ₆ ), COT is not one of the aromatic hydrocarbons because, due to the number of its π electrons, it does not conform to Hückel's rule and is also not planar, but rather has a tub shape .

Three-dimensional framework formula in all - ( Z ) - configuration with visible boat conformation

Thus, cyclooctatetraene is neither an aromatic nor an anti- aromatic . Due to the lack of aromatic stabilization, it is more comparable to the usual polyenes , however, due to the deformation of the bond angle caused by the ring strain , it is of increased reactivity.

Like 1,5-cyclooctadiene (COD), the tub-shaped COT molecule can form metal complexes as a chelating ligand . By absorbing two electrons, e.g. B. by transferring a metal , the COT becomes the planar, aromatic cyclooctatetraenyl anion C ₈ H ₈ ²⁻ with ten π electrons and thus fulfills the Hückel rule. A well-known example of a complex with planar cyclooctatetraenyl ligands is uranocene .

presentation

• COT was first synthesized from pseudopelletierin in 1905 by Richard Willstätter .

• The most common synthesis of COT is based on a Walter Reppe method by cyclotetramerizing ethyne .

• Another synthesis is based on cubane . In the presence of rhodium catalysts, the syn - tricyclooctadiene is first formed, which can then be thermally converted at 50-60 ° C. to cyclooctatetraene.

properties

By heating cyclooctatetraene 1 to 100 ° C., a mixture of the two dimeric C ₁₆ H ₁₆ compounds 2 and 3 is obtained . The dimer 2 (melting point 53 ° C) is created by a Diels-Alder reaction of two molecules of cyclooctatetraene ( 1 ). This reaction is partially reversible at high temperature. In a second step, 2 rearranges into dimer 3 (melting point 76 ° C.).

From the pentacyclic compound 3 , which has a homotropilid structural element , the C ₁₀ H ₁₀ hydrocarbon Bullvalene 4 is obtained by UV irradiation with elimination of benzene 5 .

Cyclooctatetraene is used in the synthesis of suberic acid and cyclooctane .

Individual evidence

1. ↑ ^{a b c d} Datasheet Cyclooctatetraen from AlfaAesar, accessed on January 7, 2008 ( PDF )(JavaScript required) .
2. ↑ ^{a b} Datasheet Cyclooctatetraene from Acros, accessed on February 19, 2010.
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-130.
4. ↑ ^{a b} Datasheet Cyclooctatetraene from Sigma-Aldrich , accessed on November 7, 2016 ( PDF ).
5. ↑ Frank-Gerrit Klärner: How anti-aromatic is planar cyclooctatetraene? In: Angewandte Chemie . tape 113 , no. 21 , 2001, p. 4099-4103 , doi : 10.1002 / 1521-3757 (20011105) 113: 21 <4099 :: AID-ANGE4099> 3.0.CO; 2-1 .
6. ↑ Richard Willstätter, Ernst Waser: About Cyclo-octatetraen . In: Reports of the German Chemical Society . tape 44 , no. 3 , 1911, pp. 3423-3445 , doi : 10.1002 / cber.191104403216 .
7. ^ Walter Reppe, Otto Schlichting, Karl Klager, Tim Toepel: Cyclizing Polymerization of Acetylene I. About Cyclooctatetraen . In: Justus Liebig's Annals of Chemistry . tape 560 , no. 1 , 1948, p. 1-92 , doi : 10.1002 / jlac.19485600102 .
8. ↑ L. Cessar, PE Eaton, J. Halpern: Catalysis of symmetry-restricted reactions by transition metal compounds. Valence isomerization of cubane , In J. Am. Chem. Soc. 92, 1972, pp. 3515-3518. doi : 10.1021 / ja00714a075 .
9. ↑ Gerhard Schröder: The properties of two dimeric cyclooctatetraene from melting point 53 and 76 . In: Chemical Reports . tape 97 , no. November 11 , 1964, pp. 3131 , doi : 10.1002 / cber.19640971124 .
10. ↑ Gerhard Schröder: Synthesis and properties of tricyclo [3.3.2.0 ^4.6 ] decatrien- (2.7.9) ^2.3) (Bullvalen) . In: Chemical Reports . tape 97 , no. November 11 , 1964, pp. 3140 , doi : 10.1002 / cber.19640971125 .
11. ↑ Entry on cyclooctatetraene. In: Römpp Online . Georg Thieme Verlag, accessed on September 27, 2019.