Ethylene dione

Ethylene dione or ethylenedione, also called dicarbon dioxide, ethenedione, or ethene-1,2-dione, is a chemical compound with the formula C
2
O
2
or O=C=C=O. It is an oxide of carbon (an oxocarbon), and can be described as the carbon-carbon covalent dimer of carbon monoxide.[1] It can also be thought of as the dehydrated form of glyoxylic acid (H(C=O)COOH), or a ketone of ethenone H
2
C=C=O
.

Ethylene dione
Ball-and-stick model of ethylene dione
Names
IUPAC name
Ethene-1,2-dione
Systematic IUPAC name
Ethenedione
Other names
Dicarbon dioxide

Dimeric carbon monoxide
Dimeric carbonous oxide
Dimeric carbon(II) oxide

Ethylenedione
Identifiers
3D model (JSmol)
ChemSpider
Properties
C2O2
Molar mass 56.020 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Synthesis attempts

The existence of ethylenedione was first suggested in 1913.[2] However, for over a century the compound had eluded all attempts to synthesize and observe it, and it came to be considered a purely hypothetical compound, or at best an "exceedingly coy molecule".[3]

In 2015, a research group reported the creation of ethylenedione — by using laser light to eject an electron from the corresponding stable singly-charged anion C
2
O
2
— and its spectroscopic characterization.[4] However, the reported spectrum was later found to match that of the oxyallyl diradical, (H
2
C
)
2
CO
, formed by rearrangement or disproportionation under the high-energy experimental conditions rather than simple electron loss.[5]

Theoretical investigations

Despite the existence of the closed-shell Kekulé structure, O=C=C=O, the lowest bound state of ethyledione is a triplet. It would then be a diradical, with an electronic structure motif similar to the oxygen molecule. However, when the molecule is distorted away from its equilibrium geometry, the potential surfaces of the triplet and singlet states intersect, allowing for intersystem crossing to the singlet state, which is unbound and dissociates to two ground-state CO molecules. The timescale of the intersystem crossing was predicted to be 0.5 ns,[6] making triplet ethylenedione a transient, yet spectroscopically long-lived molecule.

On the other hand, the monoanion of ethylenedione, OCCO, as well as the dianion C
2
O2−
2
, called acetylenediolate, are both stable.[7][8]

Recent theoretical computations suggest that the in situ preparation and characterization of ethylenedione may be possible through low-energy free-electron induced single-molecule engineering.[1]

Koch's glyoxylide

In the 1940s, Detroit physician William Frederick Koch claimed that he had synthesized this compound, which he called glyoxylide, and that it was an antidote to the toxins that caused a long list of ailments, including diabetes and cancer. The claims were false and the drug was classified as a fraud by the FDA.[9]

See also

References

  1. ^ a b Davis, Daly; Sajeev, Y. (2017-02-22). "Communication: Low-energy free-electron driven molecular engineering: In situ preparation of intrinsically short-lived carbon-carbon covalent dimer of CO". The Journal of Chemical Physics. 146 (8): 081101. doi:10.1063/1.4976969. ISSN 0021-9606.
  2. ^ H. Staudinger, E. Anthes, Ber. Dtsch. Chem. Ges. 1913, 46, 1426.
  3. ^ Lewars, Errol (2008), "9 – Ethenedione C2O2", Modeling Marvels, Springer
  4. ^ Andew R. Dixon, Tian Xue and Andrei Sanov (2015): "Spectroscopy of Ethylenedione", Angewandte Chemie, International Edition, volume 54, issue 30, pages 8764-8767, doi:10.1002/anie.201503423.
  5. ^ Katharine G. Lunny, Yanice Benitez, Yishai Albeck, Daniel Strasser, John F. Stanton, Robert E. Continetti (2018): "Spectroscopy of Ethylenedione and Ethynediolide: A Reinvestigation". Angewandte Chemie, International Edition, volume 57, issue 19, pages 5394-5397.doi:10.1002/anie.201801848
  6. ^ D. Schröder, C. Heinemann, H. Schwarz, J. N. Harvey, S. Dua, S. J. Blanksby, and John, H. Bowie, "Ethylenedione: An Intrinsically Short-Lived Molecule", Chem. Eur. J., 4, 2550-2557 (1998).
  7. ^ J. R. Thomas, B. J. DeLeeuw, P. O’Leary, H. F. Schaefer III, B. J. Duke, B. O’Leary "The ethylenedione anion: Elucidation of the intricate potential energy hypersurface", J. Chem. Phys, 102, 6525-6536(1995).
  8. ^ P. Pyykkö and N. Runeberg, "Ab initio studies of bonding trends: Part 8. The 26-electron A≡B-C≡Dn and the 30-electron A=B=C=Dn systems", J. Mol. Struct. THEOCHEM, 234, 269-277(1991).
  9. ^ Goodrich, William W. (October 15–16, 1986). "FDA Oral History Interview, Goodrich" (PDF) (Interview). Interviewed by Ronald T. Ottes and Fred L. Lofsvold. p. 31.
Hypothetical chemical compound

A hypothetical chemical compound is a chemical compound that has been conceived of, but is not known to have been synthesized, observed, or isolated (identified or shown to exist).

Some hypothetical compounds cannot form at all. Others might turn out to be highly unstable, decomposing, isomerizing, polymerizing, rearranging, or disproportionating. Some are thought to exist only briefly as reactive intermediates, or in vacuum (helium hydride ion...).

Some cannot hold together due to steric hindrance (tetra-tert-butylmethane) or bond stress (tetrahedrane...).

Some have no known pathway for synthesis (hypercubane...).

Some "parent compounds" have not been or cannot be isolated, even though stable structural analogs with substituents have been discovered or synthesized (borole...).

Hypothetical compounds are often predicted or expected from known compounds, such as a families of salts for which the "parent acid" is not a stable molecule, or in which salts form with some cations but not others.

Hypothetical compounds are used in some thought experiments.

Some compounds long regarded as hypothetical have later been isolated. Ethylene dione was suggested in 1913 and observed spectroscopically in 2015.

Oxocarbon

An oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen.The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (CO2) with IUPAC names carbon(II) oxide and carbon(IV) oxide respectively. Many other stable (practically if not thermodynamically) or metastable oxides of carbon are known, but they are rarely encountered, such as carbon suboxide (C3O2 or O=C=C=C=O) and mellitic anhydride (C12O9).

While textbooks will often list only the first three, and rarely the fourth, a large number of other oxides are known today, most of them synthesized since the 1960s. Some of these new oxides are stable at room temperature. Some are metastable or stable only at very low temperatures, but decompose to simpler oxocarbons when warmed. Many are inherently unstable and can be observed only momentarily as intermediates in chemical reactions or are so reactive that they can exist only in the gas phase or under matrix isolation conditions.

The inventory of oxocarbons appears to be steadily growing. The existence of graphene oxide and of other stable polymeric carbon oxides with unbounded molecular structures suggests that many more remain to be discovered.

Pentacarbon dioxide

Pentacarbon dioxide, officially penta-1,2,3,4-tetraene-1,5-dione, is an oxide of carbon (an oxocarbon) with formula C5O2 or O=C=C=C=C=C=O.

The compound was described in 1988 by Günter Maier and others, who obtained it by pyrolysis of cyclohexane-1,3,5-trione (phloroglucin, the tautomeric form of phloroglucinol). It has also been obtained by flash vapor pyrolysis of 2,4,6-tris(diazo)cyclohexane-1,3,5-trione (C6N6O3). It is stable at room temperature in solution. The pure compound is stable up to −96 °C, at which point it polymerizes.

Tetracarbon dioxide

Tetracarbon dioxide is an oxide of carbon, a chemical compound of carbon and oxygen, with chemical formula C4O2 or O=C=C=C=C=O. It can be regarded as butatriene dione, the double ketone of butatriene — more precisely 1,2,3-butatriene-1,4-dione.Butatriene dione is the fourth member of the family of linear carbon dioxides O(=C)n=O, that includes carbon dioxide CO2 or O=C=O, ethylene dione C2O2 or O=C=C=O, carbon suboxide C3O2 or O=C=C=C=O, pentacarbon dioxide C5O2 or O=C=C=C=C=C=O, and so on.

The compound was obtained in 1990 by Maier and others, by flash vacuum pyrolysis of cyclic azaketones in a frozen argon matrix. It was also obtained in the same year by Sülzle and Schwartz through impact ionization of ((CH3-)2(C4O2)(=O)2=)2 in the gas phase. Although theoretical studies indicated that the even-numbered members of the O(=C)n=O family should be inherently unstable, C4O2 is indefinitely stable in the matrix, but is decomposed by light into tricarbon monoxide C3O and carbon monoxide CO. It has a triplet ground state.

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