Dihydroxymethylidene

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Dihydroxymethylidene
Structural formula of dihydroxymethylidene
Ball and stick model of dihydroxymethylidene
Names
IUPAC name
Dihydroxymethylidene
Systematic IUPAC name
Dihydroxymethylidene[citation needed] (substitutive)
Dihydroxidocarbon(2•)[citation needed] (additive)
Other names
Carbonic(II) acid

Carbonous acid
Dihydroxycarbene

Dihydroxymethylene
Identifiers
3D model (JSmol)
ChemSpider
MeSH Dihydroxycarbene
Properties
CH2O2
Molar mass 46.03 g·mol−1
Related compounds
Related compounds
Formic acid

Lead(II) hydroxide
Orthocarbonic acid
Tin(II) hydroxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Dihydroxymethylidene is a chemical compound with formula C(OH)2. It is an unstable tautomer of formic acid. There is no evidence that this compound exists in solution, but the molecule has been detected in the gas phase.[1] Many related carbenes are known, although they are often transient.[2]

Production and properties[edit]

Dihydroxymethylidene is produced in the gas phase by high vacuum flash vacuum pyrolysis of oxalic acid:

C2O4H2 → C(OH)2 + CO2

The species is a bent molecule with an O-C-O angle of 105.6° for the C2v all trans rotamer. Although stable at 10 K, at higher temperatures it isomerizes to formic acid.

Carbonite[edit]

The conjugate base of dihydroxycarbene is the carbonite anion, [CO2]2−. Alkali metal salts, e.g., Li
2
CO
2
, K
2
CO
2
, and Cs
2
CO
2
, have been observed at 15K.[3][4] Salts of the carbonite ion would be protonated to form formic acid, rather than the carbene.

At lower metal concentrations, salts of the monovalent anions CO
2
were favored over CO2−
2
. Carbonite was not detected when sodium was used as the metal.[4] The alkali metal carbonites obtained in the cryogenic experiments decomposed to the corresponding carbonate (with release of carbon monoxide) or oxalate.[3][4] The carbonite ion is promptly converted to carbonate in the presence of oxygen.[5][6]

The presence of carbonite ions has been proposed to be relevant to the absorption of carbon monoxide on calcium oxide and magnesium oxide[5] and on ceria.[6] In the former, it has been suggested that the carbon atom attaches via a coordinate covalent bond to an oxygen atom from the substrate through its free bonds.[5] In these contexts, it appears that the carbonite ion reacts with excess carbon monoxide to form an anion with the ketene structure, O=C=CO2−
2
.[5]

Infrared spectroscopy data confirm earlier theoretical studies that the carbonite anion has a bent structure, with the O-C-O angle varying between 120 and 130 degrees depending on the context. The metal atoms interact with both oxygen atoms. However two geometrical arrangements for the lithium and cesium salts were detected, only one of them being symmetrical on the two oxygen atoms.[3][4]

References[edit]

  1. ^ Schreiner, Peter R.; Reisenauer, Hans Peter "Spectroscopic identification of dihydroxycarbene" Angewandte Chemie International Edition (2008), volume 47, 7071-7074. doi:10.1002/anie.200802105
  2. ^ M. Jones, Jr., R. A. Moss, in "Reactive Intermediate Chemistry", Edited by R. A. Moss, M. S. Platz, M. Jones, Jr., Wiley-Interscience, Hoboken, 2004.
  3. ^ a b c Zakya H. Kafafi, Robert H. Hauge, W. Edward Billups, and John L. Margrave (1983) Carbon dioxide activation by lithium metal. 1. Infrared spectra of Li+
    CO
    2
    , Li+
    C
    2
    O
    4
    , and Li2+
    2
    CO2−
    2
    in inert-gas matrices
    . Journal of the American Chemical Society, volume 183, pages 3886--3893. doi:10.1021/ja00350a025
  4. ^ a b c d Zakya H. Kafafi, Robert H. Hauge, W. Edward Billups, and John L. Margrave (1984), Carbon dioxide activation by alkali metals. 2. Infrared spectra of M+
    CO
    2
    and M2+
    2
    CO2−
    2
    in argon and nitrogen matrices
    . Inorganic Chemistry, volume 23, pages 177-183. doi:10.1021/ic00170a013.
  5. ^ a b c d M. A. Babaeva and A. A. Tsyganenko (1987), Infrared spectroscopic evidence for the formation of carbonite CO2−
    2
    ions in CO interaction with basic oxide surfaces
    Reaction Kinetics and Catalysis Letters, volume 34, issue 1, pages 9--14. doi:10.1007/BF02069193
  6. ^ a b Binet, Claude; Ahmed Badri; Magali Boutonnet-Kizling; Jean-Claude Lavalley (1994). "FTIR study of carbon monoxide adsorption on ceria: CO22− carbonite dianion adsorbed species". Journal of the Chemical Society, Faraday Transactions. 90: 1023–1028. doi:10.1039/FT9949001023.