Oxocarbon

Overview

Carbon dioxide (CO2) occurs widely in nature, and was incidentally produced by humans and nature since pre-historical times, by breathing, the combustion of carbon-containing substances and fermentation of foods such as beer and bread. It was gradually recognized as a chemical substance, formerly called spiritus sylvestris ("forest spirit") or "fixed air", by various chemists in the 17th and 18th centuries.

Carbon monoxide may occur in combustion, too, and was used (though not recognized) since antiquity for the smelting of iron from its ores. Like the dioxide, it was described and studied in the West by various alchemists and chemists since the Middle Ages. Its true composition was discovered by William Cruickshank in 1800.

Carbon suboxide was discovered by Benjamin Brodie in 1873, by passing electric current through carbon dioxide.

The fourth "classical" oxide, mellitic anhydride (C12O9), was apparently obtained by Liebig and Wöhler in 1830 in their study of mellite ("honeystone"), but was characterized only in 1913, by Meyer and Steiner. Liebig, J. and Wöhler, F. (1830), Ueber die Zusammensetzung der Honigsteinsäure Poggendorfs Annalen der Physik und Chemie, vol. 94, Issue 2, pp.161–164. Online version accessed on 2009-07-08. Bugge (1914), Chemie: En neues Kohenoxyd. Review of Meyer and Steiner's discovery of C12O9. Naturwissenschaftliche Wochenschrift, volume 13/29, issue 12, 22 March 1914, p. 188. Online version accessed on 2009-07-09.

Brodie also discovered in 1859 a fifth compound called graphite oxide, consisting of carbon and oxygen in ratios varying between 2:1 and 3:1; but the nature and molecular structure of this substance remained unknown until a few years ago, when it was renamed graphene oxide and became a topic of research in nanotechnology.

Notable examples of unstable or metastable oxides that were detected only in extreme situations are dicarbon monoxide radical (:C=C=O), carbon trioxide (CO3), carbon tetroxide (), carbon pentoxide (),{{cite journal |archive-date=2019-12-12 |access-date=2017-01-29 |archive-url=https://web.archive.org/web/20191212235135/http://www.chem.hawaii.edu/Bil301/Kaiser%20Paper/p166.pdf |url-status=dead Some of these reactive carbon oxides were detected within molecular clouds in the interstellar medium by rotational spectroscopy. H. M. Pickett E. A. Cohen B. J. Drouin J. C. Pearson (2003), Submillimeter, Millimeter, and Microwave Spectral Line Catalog. NASA/JPL, Online version accessed on 2009-07-11.

Many hypothetical oxocarbons have been studied by theoretical methods but have yet to be detected. Examples include oxalic anhydride (C2O3 or O=(C2O)=O), ethylene dione (C2O2 or O=C=C=O) and other linear or cyclic polymers of carbon monoxide (-CO-)n (polyketones), and linear or cyclic polymers of carbon dioxide (-CO2-)n, such as the dimer 1,3-dioxetanedione (C2O4).

General structure

Normally, carbon is tetravalent, while oxygen is divalent, and in most oxocarbons (as in most other carbon compounds) each carbon atom may be bound to four other atoms, while oxygen may be bound to at most two. Moreover, while carbon can connect to other carbons to form arbitrarily large chains or networks, chains of three or more oxygens are rarely if ever observed. Thus the known electrically neutral oxocarbons generally consist of one or more carbon skeletons (including cyclic and aromatic structures) connected and terminated by oxide (-O-, =O) or peroxide (-O-O-) groups.

Carbon atoms with unsatisfied bonds are found in some oxides, such as the diradical C2O or :C=C=O; but these compounds are generally too reactive to be isolated in bulk. Loss or gain of electrons can result in monovalent negative oxygen (-), trivalent positive oxygen (≡), or trivalent negative carbon (≡). The last two are found in carbon monoxide, −C≡O+. Negative oxygen occurs in most oxocarbon anions.

Linear carbon dioxides

One family of carbon oxides has the general formula CnO2, or O=(C=)nO — namely, a linear chain of carbon atoms, capped by oxygen atoms at both ends. The first members are

• CO2 or O=C=O, the well-known carbon dioxide.
• C2O2 or O=C=C=O, the unknown and extremely unstable ethylene dione.
• C3O2 or O=C=C=C=O, the metastable carbon suboxide or tricarbon dioxide.
• C4O2 or O=C=C=C=C=O, tetracarbon dioxide or 1,2,3-Butatriene-1,4-dione Günther Maier, Hans Peter Reisenauer, Heinz Balli, Willy Brandt, Rudolf Janoschek (1990): "C4O2 (1,2,3-Butatriene-1,4-dione), the First Dioxide of Carbon with an Even Number of C Atoms". Angewandte Chemie (International Edition in English), volume 29, issue 8, Pages 905–908.
• C5O2 or O=C=C=C=C=C=O, pentacarbon dioxide,

Some higher members of this family have been detected in trace amounts in low-pressure gas phase and/or cryogenic matrix experiments, specifically for n = 7Eastwood, Frank W. (1997), Gas Phase Pyrolytic Methods for the Preparation of Carbon-Hydrogen and Carbon-Hydrogen-Oxygen Compounds.. In Yannick ValléeGas Phase Reactions in Organic Synthesis.CRC Press. and n = 17, 19, and 21.Reusch, Roman (2005). Absorptionsspektroskopie von langen Kohlenstoff-Kettenmolekülen und deren Oxide in kryogenen Matrizen. Thesis, Ruprecht-Karls-Universität Heidelberg (in German)

Linear carbon monoxides

Another family of oxocarbons are the linear carbon monoxides CnO. The first member, ordinary carbon monoxide CO, seems to be the only one that is practically stable in the pure state at room temperature (though it is not thermodynamically stable at standard temperature and pressure, see Boudouard reaction). Photolysis of the linear carbon dioxides in a cryogenic matrix leads to loss of CO, resulting in detectable amounts of even-numbered monoxides such as C2O, C4O,Maier, Günter and Reisenauer, Hans Peter (2001) "Carbenes in Matrices: Specrospcopy, Structure, and Photochemical Behavior". In Udo H. Brinker (ed.), Advances in carbene chemistry, p. 135. Elsevier. and C6O. The members up to n=9 have also been obtained by electrical discharge on gaseous C3O2 diluted in argon. The first three members have been detected in interstellar space2 of ??? for CO, 6 × 10−1 for C2O (seems wrong – perhaps 6 × 10−10?), and 1.4 × 10−10 forC3O--.

When n is even, the molecules are believed to be in the triplet (cumulene-like) state, with the atoms connected by double bonds and an unfilled orbital in the first carbon — as in :C=C=O, :C=C=C=C=O, and, in general, :(C=)n=O. When n is odd, the triplet structure is believed to resonate with a singlet (acetylene-type) polar state with a negative charge on the carbon end and a positive one on the oxygen end, as in −C≡C−C≡O+, −C≡C−C≡C−C≡O+, and, in general, −(C≡C−)(n−1)/2C≡O+. Carbon monoxide itself follows this pattern: its predominant form is believed to be −C≡O+.

Radialene-type cyclic polyketones

Another family of oxocarbons that has attracted special attention are the cyclic radialene-type oxocarbons CnOn or (CO)n.

On the other hand, the anions of these oxocarbons are quite stable, and some of them have been known since the 19th century. They are

• C2O22−, acetylenediolate (Weiss and Büchner, 1963),
• C3O32−, deltate (Eggerding and West, 1976),
• C4O42−, squarate (Cohen and others, 1959),
• C5O52−, croconate (Gmelin, 1825), Leopold Gmelin (1825), Ueber einige merkwürdige, bei der Darstellung des Kaliums nach der Brunner'schen Methode, erhaltene Substanzen. Poggendorfs Annalen der Physik und Chemie, volume 4, p. 31. Online version accessed on 2009-07-08. and
• C6O62−, rhodizonate (Heller, 1837). Heller, Johann Florian (1837), Die Rhodizonsäure, eine aus den Produkten der Kaliumbereitung gewonnene neue Säure, und ihre chemischen Verhältnisse, Justus Liebigs Annalen der Pharmacie, volume 24, issue 1, pp. 1–16. Online version accessed on 2009-07-08. Löwig, Carl (1839), Chemie der organischen Verbindungen. F. Schultess, Zürich.

The cyclic oxide C6O6 also forms the stable anions of tetrahydroxy-1,4-benzoquinone (C6O64−) and benzenehexol (C6O66−), The aromaticity of these anions has been studied using theoretical methods.West, R. and Niu, J. (1969). Non-benzenoid aromatics. Vol. 1. J. Snyder (ed.). Academic Press New York.

New oxides

Many new stable or metastable oxides have been synthesized since the 1960s, such as:

• C10O8, benzoquinonetetracarboxylic dianhydride (Hammond, 1963).
• C6O6, ethylenetetracarboxylic dianhydride, a stable isomer of cyclohexanehexone (Sauer and others, 1967).
• C12O12 or C6(C2O4)3, hexahydroxybenzene trisoxalate (Verter and Dominic, 1967); stable as a tetrahydrofuran solvate.
• C10O10 or C6O2(C2O4)2, tetrahydroxy-1,4-benzoquinone bisoxalate (Verter and others, 1968); stable as a tetrahydrofuran solvate.
• C8O8 or C6O2(CO3)2, tetrahydroxy-1,4-benzoquinone biscarbonate (Nallaiah, 1984); decomposes at about 45–53 °C.
• C9O9 or C6(CO3)3, hexahydroxybenzene triscarbonate (Nallaiah, 1984); decomposes at about 45–53 °C.
• C24O6, a cyclic trimer of the biradical 3,4-dialkynyl-3-cyclobutene-1,2-dione -C≡C-(C4O2)-C≡C- (Rubin and others, 1990);
• C32O8, a tetramer of 3,4-dialkynyl-3-cyclobutene1,2-dione (Rubin and others, 1990);
• C4O6, dioxane tetraketone or dimeric oxalic anhydride (Strazzolini and others, 1998); stable in Et2O at −30 °C, decomposes at 0 °C.
• C12O6, hexaoxotricyclobutabenzene

Many relatives of these oxides have been investigated theoretically, and some are expected to be stable, such as other carbonate and oxalate esters of tetrahydroxy-1,2-benzoquinone and of the rhodizonic, croconic, squaric, and deltic acids.

Polymeric carbon oxides

Carbon suboxide spontaneously polymerizes at room temperature into a carbon-oxygen polymer, with 3:2 carbon:oxygen atomic ratio. The polymer is believed to be a linear chain of fused six-membered lactone rings, with a continuous carbon backbone of alternating single and double bonds. Physical measurements indicate that the mean number of units per molecule is about 5–6, depending on the formation temperature.

Carbon monoxide compressed to 5 GPa in a diamond anvil cell yields a somewhat similar reddish polymer with a slightly higher oxygen content, which is metastable at room conditions. It is believed that CO disproportionates in the cell to a mixture of CO2 and C3O2; the latter forms a polymer similar to the one described above (but with a more irregular structure), that traps some of the CO2 in its matrix.

Another carbon-oxygen polymer, with C:O ratio 5:1 or higher, is the classical graphite oxide and its single-sheet version graphene oxide.

[[Fullerene]] oxides and ozonides

More than 20 oxides and ozonides of fullerene are known:

• C60O (2 isomers)
• C60O2 (6 isomers)
• C60O3 (3 isomers)
• C120O
• C120O4 (4 isomers)
• C70O
• C140O and others.

References

References

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2. (2008). "The Simplest Linear-Carbon-Chain Growth by Atomic-Carbon Addition and Ring Opening Reactions". J. Phys. Chem. A.
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4. (1975). "Synthesis of Dihydroxycyclopropenone (Deltic Acid)". Journal of the American Chemical Society.
5. (1959). "Diketocyclobutanediol". Journal of the American Chemical Society.
6. Hammond P. R.. (1963). "1,4-Benzoquinone Tetracarboxylic Acid Dianhydride, C10O8: A Strong Acceptor". Science.
7. (1967). "Eine Studie der Diels-Alder-Reaktion, VI. Kinetischer Nachweis des Moleküls C6O6 (Dianhydrid der Äthylentetracarbonsäure)". Chemische Berichte.
8. (1967). "A new carbon oxide synthesis of hexahydroxybenzene tris oxalate". Tetrahedron.
9. (2006). "Dodecamethoxy- and Hexaoxotricyclobutabenzene: Synthesis and Characterization". Journal of the American Chemical Society.
10. (2006). "Fullerene oxides and ozonides". Comptes Rendus Chimie.