Orthocarbonic acid, carbon hydroxide, methanetetrol is the name given to a hypothetical compound with the chemical formulaH4CO4 or C(OH)4. 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 anionorthocarbonateCO4−4, and is therefore considered an oxoacid of carbon.
Orthocarbonic acid is highly unstable. Calculations show that it decomposes into carbonic acid and water:[2][3]
H4CO4 → H2CO3 + H2O
Orthocarbonic acid is one of the group of ortho acids that have the general structure of RC(OH)3. The term ortho acid is also used to refer to the most hydroxylated acid in a set of oxoacids.
Researchers predict that orthocarbonic acid is stable at high pressure; hence it may form in the interior of the ice giant planets Uranus and Neptune, where water and methane are common.[4]
Orthocarbonate anions
By loss of one through four protons, orthocarbonic acid could yield four anions: H3CO−4 (trihydrogen orthocarbonate), H2CO2−4 (dihydrogen orthocarbonate), HCO3−4 (hydrogen orthocarbonate), and CO4−4 (orthocarbonate).
Numerous salts of fully deprotonated CO4−4, such as Ca2CO4 (calcium orthocarbonate) or Sr2CO4 (strontium orthocarbonate), have been synthesized under high pressure conditions and structurally characterized by X-ray diffraction.[5][6][7] Strontium orthocarbonate, Sr2CO4, is stable at atmospheric pressure. Orthocarbonate is tetrahedral in shape, and is isoelectronic to orthonitrate. The C-O distance is 1.41 Å.[8]Sr3(CO4)O is an oxide orthocarbonate (tristrontium orthocarbonate oxide), also stable at atmospheric pressure.[9]
A linear polymer which can be described as a (spiro) orthocarbonate ester of pentaerythritol, whose formula could be written as [(−CH2)2C(CH2−)2 (−O)2C(O−)2]n, was synthesized in 2002.[13]
^Sagatova, Dinara; Shatskiy, Anton; Sagatov, Nursultan; Gavryushkin, Pavel N.; Litasov, Konstantin D. (2020). "Calcium orthocarbonate, Ca2CO4-Pnma: A potential host for subducting carbon in the transition zone and lower mantle". Lithos. 370–371: 105637. Bibcode:2020Litho.37005637S. doi:10.1016/j.lithos.2020.105637. ISSN0024-4937. S2CID224909120.
^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. doi:10.1021/ja017683i
^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. doi:10.1002/anie.197905511
^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. doi:10.1021/ja00164a015
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