Product Code Database
In chemistry, an oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen. West, R. (ed.) (1980), Oxocarbons. Academic Press, New York. The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (). Many other stable (practically if not thermodynamically) or metastable oxides of carbon are known, but they are rarely encountered, such as carbon suboxide ( or ) and mellitic anhydride ().
| CO Carbon monoxide | Carbon dioxide | Carbon suboxide | Mellitic anhydride |
Many 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 exist only in gas phase or have only been detected by matrix isolation.
Graphene oxide and other stable carbon oxides with unbounded molecular structures exist.
Carbon monoxide may occur in combustion, too, and was used (though not recognized) since antiquity for the smelting of iron from its . Like the dioxide, it was described and studied in the West by various and chemists since the Middle Ages. Its true composition was discovered by William Cruikshank 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 Justus Liebig and Wöhler in 1830 in their study of mellite, 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. [https://books.google.com/books?id=ZyUAAAAAMAAJ&pg=PA161 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. [https://archive.org/stream/naturwissenschaf29deut#page/187/mode/1up 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),
H. M. Pickett E. A. Cohen B. J. Drouin J. C. Pearson (2003), ''Submillimeter, Millimeter, and Microwave Spectral Line Catalog''. [[NASA]]/[[JPL]], [http://spec.jpl.nasa.gov/ftp/pub/catalog/doc/catdoc.pdf 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 (), and linear or cyclic polymers of carbon dioxide (-CO2-) n, such as the dimer 1,3-dioxetanedione (C2O4).
| C2O3 Oxalic anhydride | C2O2 Ethylene dione | C2O4 1,3-Dioxetane- dione |
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 .
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
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.
stable in solution at room temp. and pure up to −90 °C.
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 Vallée Gas 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)
When n is even, the molecules are believed to be in the triplet state (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 state (acetylene-type) polar molecule 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+.
| (CO)2 Ethylene dione | (CO)3 Cyclopropane- trione | (CO)4 Cyclobutane- tetrone | (CO)5 Cyclopentane- pentone | (CO)6 Cyclohexane- hexone |
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
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. [https://books.google.com/books?id=1oqZAAAAIAAJ&pg=PA31 Online version] accessed on 2009-07-08.
and
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.
| C10O8 Benzoquinone- tetracarboxylic dianhydride | C6O6 Ethylene- tetracarboxylic dianhydride | C10O10 Tetrahydroxy- 1,4-benzoquinone bisoxalate | |||
| C8O8 Tetrahydroxy- 1,4-benzoquinone biscarbonate | C4O6 Dioxane tetraketone | C12O12 Hexahydroxybenzene trisoxalate | |||
| C9O9 Hexahydroxybenzene triscarbonate | C24O6 Tris(3,4-dialkynyl- 3-cyclobutene- 1,2-dione) | C32O8 Tetrakis(3,4-dialkynyl- 3-cyclobutene- 1,2-dione) | |||
| C12O6 Hexaoxotricyclo- butabenzene |
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.
Carbon monoxide compressed to 5 GPa in a diamond anvil cell yields a somewhat similar Polycarbonyl 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.
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.
Terminating and repeating units of polymeric C3O2. Oligomers of C3O2 with 3 to 6 units.
fullerene_ox">
Fullerene oxides and ozonides
More than 20 oxides and ozonides of fullerene are known:
and others.
See also
|
|
