Cyclooctatetraene

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Cyclooctatetraene
Cyclooctatetraene 125px
Ball-and-stick model of cyclooctatetraene from the side
General
Systematic name 1,3,5,7-cyclooctatetraene
Other names COT, [8]-annulene
Molecular formula C8H8
SMILES C1=C/C=C\C=C/C=C\1
Molar mass 104.15 g/mol
Appearance Clear yellow
CAS number [629-20-9]
Properties
Density and phase 0.9250 g/cm³, liquid
Solubility in water immiscible
Melting point -27 °C (246 K)
Boiling point 142 - 143 °C (415 - 416 K)
Hazards
MSDS External MSDS
EU classification Flammable (F)
Carc. Cat. 1
Muta. Cat. 2
Toxic (T)
NFPA 704 File:Nfpa h3.pngFile:Nfpa f4.pngFile:Nfpa r0.png
R-phrases
S-phrases S53, S45
Flash point −11 °C
Autoignition temperature 561 °C
RTECS number CY1400000
Related compounds
Related
hydrocarbons
cyclooctane
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

1,3,5,7-Cyclooctatetrene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of its stoichiometric relationship to benzene, COT has been the subject of much research and some controversy.

Unlike benzene, C6H6, however, cyclooctatetraene, C8H8, is not aromatic. Its reactivity is characteristic of an ordinary polyene, i.e. it undergoes addition reactions. Benzene, by contrast, characteristically undergoes substitution reactions, not additions.

History

1,3,5,7-cyclooctatetrene was initially synthesized by Richard Willstätter at Munich in 1905. [1][2]

File:WillstatterSynthesis.png
Willstatter synthesis

Willstätter noted that the compound did not exhibit the expected aromaticity. Between 1939 and 1943, chemists throughout the US unsuccessfully attempted to synthesize COT. They rationalized their lack of success with the conclusion that Willstätter had not actually synthesized the compound but instead its isomer, styrene. Willstätter responded to these reviews in his autobiography, where he noted that the American chemists were 'untroubled' by the reduction of his cyclooctatetraene to cyclooctane (a reaction impossible for styrene). In 1947, Walter Reppe at Ludwigshafen at last repeated Willstätter's synthesis.[3]

Structure and Bonding

Cyclooctatetraene in its native "tub-shaped" conformation.

Early studies demonstrated that COT did not display the chemistry of an aromatic compound [4], yet early electron diffraction experiments concluded that the C-C bond distances were identical [5]. However, X-Ray diffraction data from H.S. Kaufman demonstrated cyclooctatetraene to contain two distinct C-C bond distances [6]. This result indicated that COT is an annulene with fixed alternating single and double C-C bonds. In its normal state, cyclooctatetraene is non-planar and adopts a tub-shaped confirmation.

Chemistry

File:Reppe synthesis.jpg
Reppe's Reaction

Richard Willstätter's original synthesis (4 consecutive elimination reactions on a cycloctane framework) gives relatively low yields. Reppe's synthesis of cyclooctatetraene involved treating acetylene at high pressure with a warm mixture of nickel cyanide and calcium carbide was much better, with chemical yields near 90% [3]

Because COT is unstable and easily forms explosive organic peroxides, a small amount of hydroquinone is usually added to commercially available material. Testing for peroxides is advised when using a previously opened bottle; white crystals around the neck of the bottle may be composed of the peroxide, which may explode when mechanically disturbed.

COT reacts with peroxy acids, yielding epoxides. It easily undergoes addition reactions. Furthermore, a stable polyacetylene has been synthesized via the ring-opening polymerization of an alkyl-substituted cyclooctatetraene.[7]

Cyclooctatetraenide anion

COT readily reacts with potassium metal to form the salt K2COT, which contains the dianion C8H82−. The dianion is both planar in shape and aromatic with a Huckel electron count of 10. Cyclooctatetraene forms complexes with some metals, including yttrium and lanthanides. One-dimensional Eu-COT sandwiches have been described as nanowires [8]. The sandwich compounds U(COT)2, or uranocene and Fe(COT)2, are known.

The compound Fe(COT)2, when refluxed in toluene with dimethylsulfoxide and Dimethoxyethane for 5 days, is found to form magnetite and crystalline carbon also containing carbon nanotubes [9]

Because COT changes conformation between tub-shaped and planar with addition or subtraction of electrons, it could, in principle, be used to construct artificial muscles. Such devices have been contemplated to be makeable by grafting COT derivatives to a backbone of a suitable conducting polymer, which would supply or remove the reducing equivalents [10].

See also

References

  1. Mason, S. "The Science and Humanism of Linus Pauling (1901-1994)", Chemical Society Reviews 26, 1 (February 1997).
  2. Richard Willstätter, Ernst Waser (1911). "Über Cyclo-octatetraen". Berichte der deutschen chemischen Gesellschaft. 44 (3): 3423–3445. doi:10.1002/cber.191104403216.
  3. 3.0 3.1 Walter Reppe, Otto Schlichting, Karl Klager, Tim Toepel (1948). "Cyclisierende Polymerisation von Acetylen I Über Cyclooctatetraen". Justus Liebigs Annalen der Chemie. 560 (1): 1–92. doi:10.1002/jlac.19485600102.
  4. Johnson, A.W., Sci. Progress; 506; 1947; 35.
  5. Bastiensen, O. et al. Nature; 128; 1947; 160.
  6. Kaufman, H.S., Fankuchen, I., & Mark, H. Nature; 161; 1948; 165.
  7. U.S. Patent 5,198,153
  8. http://www.nanostruct-mater.jst.go.jp/highlights-e/2004/hilite_nakajima-01.html
  9. Crystalline Graphite from an Organometallic Solution-Phase Reaction Erich C. Walter, Tobias Beetz, Matthew Y. Sfeir, Louis E. Brus, and Michael L. Steigerwald J. Am. Chem. Soc.; 2006; 128(49) pp 15590 - 15591; (Communication) doi: 10.1021/ja0666203
  10. http://www.fiatlux.ucr.edu/cgi-bin/display.cgi?id=469

10. Experimental/Computational Study of the Electrochemical Oxidation of Cyclooctatetraene in Protic Media. Solvent Effects, Grayson Connors, Xin Wu, Albert J. Fry. J. Am. Chem. Soc.; 2007; http://pubs.acs.org/cgi-bin/asap.cgi/orlef7/asap/html/ol070349s.html

External links

ar:سيكلو أوكتا تيتراين de:Cyclooctatetraen


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