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| Names | |
|---|---|
| Preferred IUPAC name Propa-1,2-diene-1,3-dione | |
| Identifiers | |
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3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| MeSH | Carbon+suboxide |
| UNII | |
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| Properties | |
| C3O2 | |
| Molar mass | 68.031 g·mol−1 |
| Appearance | colorless gas |
| Odor | strong, pungent odor |
| Density | 3.0 kg/m3, gas[1] 1.114 g/cm3, liquid[2] |
| Melting point | −111.3 °C (−168.3 °F; 161.8 K) |
| Boiling point | 6.8 °C (44.2 °F; 279.9 K) |
| reacts | |
| Solubility | soluble in1,4-dioxane,ether,xylene,CS2,tetrahydrofuran |
Refractive index (nD) | 1.4538 (6 °C) |
| 0 D | |
| Structure | |
| rhombic | |
| quasilinear (phase dependent) | |
| Thermochemistry | |
| 66.99 J/mol K | |
Std molar entropy(S⦵298) | 276.1 J/mol K |
Std enthalpy of formation(ΔfH⦵298) | −93.6 kJ/mol |
| Related compounds | |
Related oxides | carbon dioxide carbon monoxide dicarbon monoxide |
Related compounds | carbon subsulfide carbon subnitride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Carbon suboxide, ortricarbon dioxide, is anorganic,oxygen-containing chemical compound withformulaC3O2 andstructureO=C=C=C=O. Its 4 cumulativedouble bonds make it acumulene. It is one of the stable members of the series of linearoxocarbonsO=Cn=O, which also includescarbon dioxide (CO2) andpentacarbon dioxide (C5O2). Although if carefully purified it can exist at room temperature in the dark without decomposing, it willpolymerize under certain situations.
The substance was discovered in 1873 byBenjamin Brodie by subjectingcarbon monoxide to an electric current. He claimed that the product was part of a series of "oxycarbons" with formulasCx+1Ox, namelyC2O,C3O2,C4O3,C5O4, …, and to have identified the last two;[3][4] however, onlyC3O2 is known. In 1891Marcellin Berthelot observed that heating pure carbon monoxide at about 550 °C created small amounts of carbon dioxide but no trace of carbon, and assumed that a carbon-rich oxide was created instead, which he named "sub-oxide". He assumed it was the same product obtained by electric discharge and proposed the formulaC2O.[5]Otto Diels later stated that the more organic names dicarbonylmethane and dioxallene were also correct.
It is commonly described as an oily liquid or gas at room temperature with an extremely noxious odor.[6]
It is synthesized by warming a dry mixture ofphosphorus pentoxide (P4O10) andmalonic acid or itsesters.[7]Therefore, it can be also considered as the anhydride ofmalonic anhydride, i.e. the "second anhydride" of malonic acid.[8]
Several other ways for synthesis and reactions of carbon suboxide can be found in a review from 1930 by Reyerson.[6]
Carbon suboxide polymerizes spontaneously to a red, yellow, or black solid. The structure is postulated to be poly(α-pyronic), similar to the structure in2-pyrone (α-pyrone).[9][10] The number of monomers in the polymers is variable (seeOxocarbon#Polymeric carbon oxides).In 1969, it was hypothesized that the color of the Martian surface was caused by this compound; this was disproved by theViking Mars probes (the red color is instead due toiron oxide).[11]
Carbon suboxide is used in the preparation ofmalonates; and as an auxiliary to improve the dye affinity of furs.
Inchemical synthesis, carbon suboxide is a1,3-dipole, reacting with alkenes to make 1,3‑cyclopentadiones. Because it is so unstable, it is a reagent of last resort.[12]
Carbon suboxide, C3O2, can be produced in small amounts in any biochemical process that normally producescarbon monoxide, CO, for example, during heme oxidation by heme oxygenase-1. It can also be formed from malonic acid. It has been shown that carbon suboxide in an organism can quickly polymerize into macrocyclic polycarbon structures with the common formula (C3O2)n (mostly(C3O2)6 and(C3O2)8), and that those macrocyclic compounds are potent inhibitors of Na+/K+-ATP-ase and Ca-dependent ATP-ase, and havedigoxin-like physiological properties and natriuretic and antihypertensive actions. Those macrocyclic carbon suboxide polymer compounds are thought to be endogenous digoxin-like regulators of Na+/K+-ATP-ases and Ca-dependent ATP-ases, and endogenous natriuretics and antihypertensives.[13][14][15] Other than that, some authors think also that those macrocyclic compounds of carbon suboxide can possibly diminish free radical formation and oxidative stress and play a role in endogenous anticancer protective mechanisms, for example in theretina.[16]
The structure of carbon suboxide has been the subject of experiments and computations since the 1970s. The central issue is the question of whether the molecule is linear or bent (i.e., whether). Studies generally agree that the molecule is highly non-rigid, with a very shallow barrier to bending. According to one study, the molecular geometry is described by a double-well potential with a minimum atθC2 ~ 160°, an inversion barrier of 20 cm−1 (0.057 kcal/mol), and a total energy change of 80 cm−1 (0.23 kcal/mol) for 140° ≤θC2 ≤ 180°.[17] The small energetic barrier to bending is around the same order of magnitude as the vibrationalzero-point energy. Therefore, the molecule is best described asquasilinear. While infrared[18] and electron diffraction[19] studies have indicated thatC3O2 has a bent structure in the gas phase, the compound was found to possess at least an average linear geometry in the solid phase by X-ray crystallography, although the large thermal ellipsoids of the oxygen atoms and C2 have been interpreted to be consistent with rapid bending (minimumθC2 ~ 170°), even in the solid state.[10]
A heterocumulene resonance form of carbon suboxide based on minimization of formal charges does not readily explain the molecule's non-rigidity and deviation from linearity. To account for the quasilinear structure of carbon suboxide, Frenking has proposed that carbon suboxide be regarded as a "coordination complex" of carbon(0) bearing two carbonyl ligands and two lone pairs:.[20] However, the contribution of dative bonding inC3O2 and similar species has been criticized as chemically unreasonable by others.[21]
When pure and dry carbonic oxide [=carbon monoxide] is circulated through the induction-tube, and there submitted to the action of electricity, a decomposition of the gas occurs [...] Carbonic acid [=carbon dioxide] is formed, and simultaneously with its formation a solid deposit may be observed in the induction-tube. This deposit appears as a transparent film of a red-brown color, lining the walls of the tube. It is perfectly soluble in water, which is strongly colored by it. The solution has an intensely acid reaction. The solid deposit, in the dry condition before it has been in contact with the water, is an oxide of carbon.
