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Carbon suboxide, or tricarbon dioxide, is an organic,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
-containing chemical compound with formula and structure . Its four cumulative
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
s make it a
cumulene In organic chemistry, a cumulene is a compound having three or more ''cumulative'' (consecutive) double bonds. They are analogous to allenes, only having a more extensive chain. The simplest molecule in this class is butatriene (), which is al ...
. It is one of the stable members of the series of linear
oxocarbon In chemistry, 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 (). Many other stable (practically if not thermodynamica ...
s , which also includes
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
() and
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 cyclohexa ...
(). Although if carefully purified it can exist at room temperature in the dark without decomposing, it will
polymerize In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many for ...
under certain conditions. The substance was discovered in 1873 by Benjamin Brodie by subjecting
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
to an electric current. He claimed that the product was part of a series of "oxycarbons" with formulas , namely , , , , …, and to have identified the last two; however, only is known. In 1891
Marcellin Berthelot Pierre Eugène Marcellin Berthelot (; 25 October 1827 – 18 March 1907) was a French chemist and Republican politician noted for the ThomsenBerthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substa ...
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 formula .
Otto Diels Otto Paul Hermann Diels (; 23 January 1876 – 7 March 1954) was a German chemist. His most notable work was done with Kurt Alder on the Diels–Alder reaction, a method for diene synthesis. The pair was awarded the Nobel Prize in Chemis ...
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.


Synthesis

It is synthesized by warming a dry mixture of
phosphorus pentoxide Phosphorus pentoxide is a chemical compound with molecular formula P4 O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydra ...
() and
malonic acid Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid' ...
or its
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s. Therefore, it can be also considered as the anhydride of
malonic anhydride Malonic anhydride or oxetane-2,4-dione is an organic compound with chemical formula C3H2O3 or CH2(CO)2O. It can be viewed as the anhydride of malonic acid, or a double ketone of oxetane. Malonic anhydride was first synthesized in 1988 by ozonolys ...
, i.e. the "second anhydride" of malonic acid. Several other ways for synthesis and reactions of carbon suboxide can be found in a review from 1930 by Reyerson.


Polymerization

Carbon suboxide polymerizes spontaneously to a red, yellow, or black solid. The structure is postulated to be poly(α-pyronic), similar to the structure in 2-pyrone (α-pyrone). The number of monomers in the polymers is variable (see Oxocarbon#Polymeric carbon oxides). In 1969, it was hypothesized that the color of the Martian surface was caused by this compound; this was disproved by the Viking Mars probes (the red color is instead due to iron oxide).


Uses

Carbon suboxide is used in the preparation of
malonate The conjugate acids are in :Carboxylic acids. {{Commons category, Carboxylate ions, Carboxylate anions Carbon compounds Oxyanions ...
s; and as an auxiliary to improve the dye affinity of furs.


Biological role

Carbon suboxide, C3O2, can be produced in small amounts in any biochemical process that normally produces
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, 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 ()n (mostly and ), and that those macrocyclic compounds are potent inhibitors of Na+/K+-ATP-ase and Ca-dependent ATP-ase, and have digoxin-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. 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 the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
.


Structure and bonding

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 \theta_ = \angle C1C2C3 \ \overset\ 180\!^\circ). 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 at ''θ''C2 ~ 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° ≤ ''θ''C2 ≤ 180°. The small energetic barrier to bending is around the same order of magnitude as the vibrational
zero-point energy Zero-point energy (ZPE) is the lowest possible energy that a quantum mechanical system may have. Unlike in classical mechanics, quantum systems constantly fluctuate in their lowest energy state as described by the Heisenberg uncertainty pri ...
. Therefore, the molecule is best described as ''quasilinear.'' While infrared and electron diffraction studies have indicated that 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 (minimum ''θ''C2 ~ 170°), even in the solid state. 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: OC:->\overset<-:CO. However, the contribution of dative bonding in and similar species has been criticized as chemically unreasonable by others.


References


External links


WebElements page on compound's properties
* {{DEFAULTSORT:Carbon Suboxide Oxocarbons Gaseous signaling molecules Heterocumulenes Enones Ketenes Diketones Foul-smelling chemicals