Meldrum's acid
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IUPAC name
2,2-Dimethyl-1,3-dioxane-4,6-dione
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3D model (Jmol)
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| ECHA InfoCard | 100.016.358 |
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PubChem CID
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| Properties | |
| C6H8O4 | |
| Molar mass | 144.13 g·mol−1 |
| Melting point | 94 to 95 °C (201 to 203 °F; 367 to 368 K) (decomposes) |
| Acidity (pKa) | 4.97 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Meldrum's acid or 2,2-dimethyl-1,3-dioxane-4,6-dione is an organic compound. The compound was first made in 1908 by Andrew Norman Meldrum by a condensation reaction of malonic acid with acetone in acetic anhydride and sulfuric acid. Meldrum misidentified the structure as a β-lactone of β-hydroxyisopropylmalonic acid. The correct structure is shown on this page.
As an alternative to its original preparation, Meldrum's acid can be synthesized from malonic acid, isopropenyl acetate, and catalytic sulfuric acid. Meldrum's acid has a high acidity with a pKa of 4.97. Meldrum's acid high acidity was long considered "anomalous" given it is 8 orders of magnitude more acidic than the highly related compound, dimethyl malonate (whose aqueous pKa is around 13). In 2004, Ohwada and coworkers resolved the Meldrum acid anomaly by performing several calculations. Ohwada noticed that the energy-minimizing conformation structure of the compound places the alpha proton's σCH orbital in the proper geometry to align with the π*CO, so that the ground state poses unusually strong destabilization of the C-H bond.
Because of its great acidity, Meldrum's acid, like malonic acid, can serve as a reactant in Knoevenagel condensations.
Meldrum's acid displays thermal instability. At high temperatures, Meldrum's acid undergoes a pericyclic reaction that releases acetone and carbon dioxide and produces a highly reactive ketene compound. Ketene intermediates can be isolated using flash vacuum pyrolysis (FVP) of Meldrum's acid at high temperatures. These highly electrophilic ketenes allow various chemical reactions to take place by reacting the unstable ketene with other chemicals. Alternately, the pyrolysis can be performed in solution, allowing a one-pot reaction with chemicals already present rather than isolating the unstable ketene intermediate. With relative simplicity, is possible to form new C–C bonds, rings, amides, esters, and acids. The ability to form such diverse products makes Meldrum's acid a very useful reagent for synthetic chemists.
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