Tricarbon monoxide

Tricarbon monoxide

Names
Preferred IUPAC name 3-Oxopropa-1,2-dien-1-ylidene
Other names 3-Oxopropadienylidene
Identifiers
CAS Number	11127-17-6 [1]
3D model (JSmol)	Interactive image
PubChem CID	101860484
CompTox Dashboard (EPA)	DTXSID301336916
InChI InChI=1S/C3O/c1-2-3-4 Key: ZCNKODXATWVMAO-UHFFFAOYSA-N
SMILES [C-]#CC#[O+]
Properties
Chemical formula	C3O
Molar mass	52.032 g·mol−1
Appearance	Gas
Related compounds
Related oxides	carbon monoxide dicarbon monoxide tetracarbon monoxide
Related compounds	tricarbon monosulfide carbon subnitride HCCCO[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Tricarbon monoxide C₃O is a reactive radical oxocarbon molecule found in space, and which can be made as a transient substance in the laboratory. It can be trapped in an inert gas matrix or made as a short lived gas. C₃O can be classified as a ketene or an oxocumulene a kind of heterocumulene.^[3]

C₃O has been detected by its microwave spectrum in the dark cold Taurus Molecular Cloud One^[4] and also in the protostar Elias 18.^[5]

The route to produce this is speculated to be:^[6]

HC⁺
₃ + CO₂ → HC₃O⁺ + CO

HC₃O⁺ → C₃O + H⁺

or^[5]

C₂ + CO → C₃O which is more favourable at lower temperatures.

The related C₃S is more abundant in dark molecular clouds, even though oxygen is 20 times more common than sulfur. The difference is due to the higher rate of formation and that C₃S is less polar.^[5]

C₃O can be produced by heating Meldrum's acid. This also produces acetone, carbon monoxide and carbon dioxide.^[7]

R. L. DeKock and W. Waltner were the first to identify C₃O by reacting atomic carbon with carbon monoxide in an argon matrix. They observed an infrared absorption line at 2241 cm⁻¹.^[7] They produced carbon atoms by heating graphite inside a thin tantalum tube.^[8]

M. E. Jacox photolysed C₃O₂ in an argon matrix to produce C₃O with an IR absorption line at 2244 cm⁻¹, however he did not recognise what was produced.^[8]

By heating diazocyclopentanetrione or a similar acid anhydride, (2,4-azo-3-oxo-dipentanoic anhydride), C₃O is produced. Also the action of light on tetracarbon dioxide yields C₃O and CO.^[9]

Heating fumaryl chloride also yields C₃O.^[3] Heating Lead 2,4-dinitroresorcinate also produces C₃O along with C₂O, CO and carbon suboxide.^[10] An electric discharge in carbon suboxide produces about 11 ppm C₃O.^[11]

Roger Brown heated 3,5-dimethyl-1-propynolpyrazole to over 700 °C to make C₃O.^[12] Also pyrolysis of 5,5'-bis(2,2-dimethyl-4,6-dioxo-1,3-dioxanylidene or di-isopropylidene ethylenetetracarboxylate yields C₃O.^[12]

Irradiating carbon monoxide ice with electrons yields a mixture of carbon oxides, including C₃O. This process could happen on icy bodies in space.^[13]

Irradiating cyclopropenone with vacuum ultraviolet while frozen in a neon matrix causes dehydrogenation to form CCCO. Hydrogen can then react again to yield isomers propynal and propadienone.^[14]

C₃O can be stabilised as a ligand in the pentacarbonyls of group 6 elements as in Cr(CO)₅CCCO. This is formed from [n-Bu₄N][CrI(CO)₅] and the silver acetylide derivative of sodium propiolate (AgC≡CCOONa), and then thiophosgene. AgC≡CCOONa in turn is made from silver ions and sodium propiolate.^[15] The blue black solid complex is called pentacarbony1(3-oxopropadienylidene)chromium(0). It is quite volatile and decomposes at 32 °C. Its infrared spectrum shows a band at 2028 cm⁻¹ due to CCCO. The complex can dissolve in hexane, however it slowly decomposes, losing dicarbon (C₂) which goes on to form acetylenes and cumulenes in the solvent. Dimethyl sulfoxide oxidises the CCCO ligand to carbon suboxide./^[16]

C₃O deposits a reddish-black film on glass.^[12]

The reaction of C₃O and urea is predicted to form uracil.^[17] The pathway for this, is that firstly the two molecules react to form isocyanuric acid and propiolamide, the NH then reacts to bond with the triple bond, with the NH₂ group moving back. Then a final cyclisation occurs to make uracil.^[18]

The C₃O molecules do not last long. At the low pressure of 1 pascal, they survive about one second.^[19] The force constants for the bonds are: C1-O 14.94, C1-C2 1.39 C2-C3 6.02 mdyn/Å.^[8] The bond lengths are C-O 1.149, C1-C2 1.300, C2-C3 1.273 Å. The molecule is linear.^[6]

Proton affinity is 885 kJmol⁻¹.^[6] The dipole moment is 2.391 D.^[15] The oxygen end has a positive charge, and the carbon end the negative charge.^[6] The molecule behaves as if there are triple bonds at each end, and a single bond in the middle. This is isoelectronic to cyanogen.^[20]

Molecular constants used in determining the microwave spectrum are rotational constant B₀=4810.8862 MHz centrifugal distortion constant D₀=0.00077 MHz. Known microwave spectral lines vary from 9621.76 for J=1←0 to 182792.35 MHz for J=19←18.^[11]