Orthocarbonic acid (also known as methanetetrol) is a chemical compound with the chemical formula or . Its molecular structure consists of a single carbon atom bonded to four hydroxyl groups. It would be therefore a fourfold alcohol. In theory, it could lose four protons to give the hypothetical oxocarbon anion orthocarbonate , and is therefore considered an oxoacid of carbon.
Orthocarbonic acid is highly unstable and long held to be a hypothetical chemical compound. Calculations show that it decomposes into carbonic acid and water:Carboxylic Acids and Derivatives
However, orthocarbonic acid was first synthesized in 2025 from the electron-irradiation of a frozen mixture of water and carbon dioxide and identified by mass spectrometry.
Researchers predict that orthocarbonic acid is stable at high pressure; thus, it may form in the interior of the ice giant planets Uranus and Neptune, where water and methane are common.
Orthocarbonate anions By loss of one through four protons, orthocarbonic acid could yield four anions: (trihydrogen orthocarbonate), (dihydrogen orthocarbonate), (hydrogen orthocarbonate), and (orthocarbonate).
Numerous salts of fully deprotonated , such as (calcium orthocarbonate) or (strontium orthocarbonate), have been synthesized under high pressure conditions and structurally characterized by X-ray diffraction. Strontium orthocarbonate, , is stable at atmospheric pressure. Orthocarbonate is tetrahedral in shape, and is isoelectronic to orthonitrate. The C-O distance is 1.41 Å. is an oxide orthocarbonate (tristrontium orthocarbonate oxide), also stable at atmospheric pressure.
Orthocarbonate esters The tetravalent moiety is found in stable organic compounds; they are formally esters of orthocarbonic acid, and therefore are called orthocarbonates. For example, tetraethoxymethane can be prepared by the reaction between chloropicrin and sodium ethoxide in ethanol.Orthocarbonic acid, tetraethyl ester Organic Syntheses, Coll. Vol. 4, p. 457 (1963); Vol. 32, p. 68 (1952). Polyorthocarbonates are stable polymers that might have applications in absorbing organic solvents in waste treatment processes, or in dental restorative materials. The explosive trinitroethylorthocarbonate possesses an orthocarbonate core.
A linear polymer which can be described as a (spiro) orthocarbonate ester of pentaerythritol, whose formula could be written as , was synthesized in 2002.David T. Vodak, Matthew Braun, Lykourgos Iordanidis, Jacques Plévert, Michael Stevens, Larry Beck, John C. H. Spence, Michael O'Keeffe, Omar M. Yaghi (2002): "One-Step Synthesis and Structure of an Oligo(spiro-orthocarbonate)". Journal of the American Chemical Society, volume 124, issue 18, pages 4942–4943.
The carbon atom in the spiro ester bis-catechol orthocarbonate was found to have tetrahedral bond geometry, contrasting with the square planar geometry of the silicon atom in the analogous orthosilicate ester.H. Meyer, G. Nagorsen (1979): "Structure and reactivity of the orthocarbonic and orthosilicic acid esters of pyrocatechol". Angewandte Chemie International Edition in English, volume 18, issue 7, pages 551-553.
Orthocarbonates may exist in several conformers, that differ by the relative rotation of the C–O–C bridges. The conformation structures of some esters, such as tetraphenoxymethane, tetrakis(3,5-dimethyl-phenoxy)methane, and tetrakis(4-bromophenoxy)methane have been determined by X-ray diffraction.N. Narasimhamurthy, H. Manohar, Ashoka G. Samuelson, Jayaraman Chandrasekhar (1990): "Cumulative anomeric effect: A theoretical and x-ray diffraction study of orthocarbonates". Journal of the American Chemical Society, volume 112, issue 8, pages 2937–2941.
See also Pentaerythritol, Orthosilicic acid, Carbonic acid,
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