General
Systematic name	1,3,5,7-cyclooctatetraene
Other names	COT, *-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	*
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)
Related compounds
Related hydrocarbons	cyclooctane
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Chemical infobox

1,3,5,7-cyclooctatetrene (COT) is an unsaturated derivative of cyclooctane, with the formula C₈H₈. It is also known as ^*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-cyclooctatriene was initially synthesized by Richard Willstätter at Munich in 1905. 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.

Structure and Bonding

---

Early studies demonstrated that COT did not display the chemistry of an aromatic compound, yet early electron diffraction experiments concluded that the C-C bond distances were identical. However, X-Ray diffraction data from H.S. Kaufman demonstrated cyclooctatetraene to contain two distinct C-C bond distances. 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.

Preparation

---

Richard Willstätter's original synthesis reaction 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 yields near 90%.

Properties and uses

---

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 readily reacts with potassium metal to form the salt K₂COT, which contains the dianion C₈H₈^2-. The dianion is both planar in shape and aromatic. COT also 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.

Cyclooctatetraene forms complexes with some metals, including yttrium and lanthanides. One-dimensional Eu-COT sandwiches have been described as nanowires. The sandwich compound U(COT)₂, or uranocene, is known.

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.

See also

---

• Cyclobutadiene
• Semibullvalene is an isomer.

References

---

1. Reppe, et al.; JLACBF; Justus Liebigs Ann. Chem.; 560; 1948; 1, 41.
2. Mason, S. "The Science and Humanism of Linus Pauling (1901-1994)", Chmical Society Reviews 26, 1 (February 1997).
3. Johnson, A.W., Sci. Progress; 506; 1947; 35.
4. Bastiensen, O. et al. Nature; 128; 1947; 160.
5. Kaufman, H.S., Fankuchen, I., & Mark, H. Nature; 161; 1948; 165.
6. US Patent #5198153, ^*
7. http://www.nanostruct-mater.jst.go.jp/highlights-e/2004/hilite_nakajima-01.html
8. http://www.fiatlux.ucr.edu/cgi-bin/display.cgi?id=469

Annulenes | Molecular electronics | سيكلو أوكتا تيتراين | Cyclooctatetraen